[Radio Sets Scr-193-A, Scr-193-B, Scr-193-C, Scr-193-D, and Scr-193-E]
[From the U.S. Government Publishing Office, www.gpo.gov]
UJI.35:1I-X73
Document Reserve
TM 11-273
NON-CIRCULATING
WAR DEPARTMENT
TECHNICAL MANUAL
RADIO SETS SCR-193-A, SCR-193-B SCR-193-C, SCR-193 D, AND SCR-193-E
April 12,1941
NTSU LIBRARY
TM 11-273
TECHNICAL MANUAL! WAR DEPARTMENT,
No. 11-273 | Washington, April 12, 1941.
RADIO SETS SCR-193-A,
SCR-193-B, SCR-193-C, SCR-193-D, and SCR-193-E
Section I. General. Paragraph
Purpose_______________________________________ 1
Power_________________________________________ 2
Modes of transmission and reception___________ 3
Distance ranges_______________________________ 4
Frequency ranges______________i------------ 5
Channels______________________________________ 6
Use___________________________________________ 7
Transport__________________________'------- 8
Supply_______________________________________ 9
Weight and volume____________________________ 10
Major components_____________________________ 11
Radio transmitters BC-191-A and BC-191-C, and transmitter tuning units TU-5-A and TU-6-A_____________._•_____________•________ 12
Radio receivers BC-312 and BC-312-C------- 13
Control box BC-321_________________________ 14
Radio control box BC-309___________________ 15
Dynamotor units BD-77-A and BD-77-B________ 16
Mast sections MS-49 to MS-53, and mast base MP-37__________________________________ 17
Case CS-48, and boxes BX-8, BX-19, and BX-21_______________________________________ 18
Covers BG-67, BG-75,BG-78,BG-79,BG-84, and rolls BG-56, BG-56-A, and cabinet CH-60_______________________________________ 19
Vehicular accessories_____________________ 20
II. Employment. Limitations__________________________________:---- 21
Installation_________________________________ 22
Check and adjustments prior to operation___ 23
Operation in general_________________________ 24
Transmitting-_•______________________________ 25
Receiving____________________________________ 26
Care and adjustments_________________________ 27
Storage______________________________________ 28
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TH 11-273
SIGNAL CORPS
III. Detailed functioning of parts. Paragraph
Radio transmitters BC-191-A and BC-191-C, and transmitter timing units TU-5-A and
TU-6-A__________________________________ 29
Dynamotor units BD-77-A and BD-77-B__ 30
Radio receivers BC-312 and BC-312-C_______ 31
IV. Servicing and repair.
Servicing____________________________________ 32
Inspections__________________________________ 33
Lubrication__________________________________ 34
Special adjustments to radio transmitters
BC-191-A andBC-191-C_______________________ 35
Normal current, resistance, and voltage readings ______________________________________ ‘ 36
Procedure in case of set failure_____________ 37
Locating trouble_____________________________ 38
Repairs______________________________________ 39
V, Lists of parts.
Components, weights, and dimensions_______ 40
Replaceable parts____________________________ 41
Section I
GENERAL Paragraph
Purpose______________________________________________________________ 1
Power_________________________________________________________________ 2
Modes of transmission and reception__________________________________ 3
Distance ranges_______________________________________________________ 4
Frequency ranges______________________________________________________ 5
Channels______________________________________________________________ 6
Use________________________________________________________________ 7
Transport_____________________________________________________________ 8
Supply______________________________________________________________ 9
Weight and volume______________________________________;_____________ 10
Major components_____________________________________________________ 11
Radio transmitters BC-191-A and BC-191-C, and transmitter tuning units
TU-5-A and T U-6-A_________________________________________________ 12
Radio receivers BC-312 and BC-312-C__________________________________ 13
Control box BC-321___________________________________________________ 14
Radio control box BC-309__________________________________________ 15
Dynamotor units BD-77-A and BD-77-B__________________________________ 16
Mast sections MS-49 to MS-53, and mast base MP-37____________________ 17
Case CS-48, andboxes BX-8, BX-19, and BX-21_______________________ 18
Covers BG-67, BG-75, BG-78, BG-79, BG-84, and rolls BG-56, BG—56-A, and cabinet CH-60____________________________________________________ 19
Vehicular accessories________________________________________________ 20
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TM 11-373
RADIO SETS SCR-193-A, ETC. 1-4
1. Purpose.—Radio sets SCR-193-A, SCR-193-B, SCR-193-C, SCR-193-D, and SCR-193-E are designed for installation in vehicles for the purpose of providing intervehicular communication whether the vehicles are stationary or moving. Modifications may appear from time to time to adapt these radio sets to new types of vehicles, in which case suitable changes in this manual will be issued.
a. Radio sets SCR-193-A, SCR-193-B, SCR-193-C, SCR-193-D, and SCR-193-E are designed for use in light tank M2 A3, scout car M3, combat car M1A1, scout car M3A1, and truck, %-ton, 4x4, command (radio), respectively. These sets may also be installed in other vehicles if a proper battery is available and if proper shielding against ignition noises is provided. These radio sets have been assigned different type numbers because of minor differences in component parts necessary to effect suitable installations in the particular vehicles concerned.
b. The information and instructions herein apply equally to all radio sets covered by this manual unless a particular one is specifically referred to by type number.
2. Power.—a. Input.—The primary source of power required to operate the transmitters and receivers of these sets is the 12-volt vehicular storage battery (not a radio set component). For normal storage battery current consumption of the receivers and transmitters under various modes of operation, see paragraph 36.
b. Output.—The transmitters have a nominal output rating of 75 watts.
3. Modes of transmission and reception.—These radio sets transmit and receive the following:
a. Continuous-wave telegraph signals, abbreviated as “c. w.”
b. Tone-modulated, continuous-wave telegraph signals, abbreviated as “tone.”
c. Voice-modulated, continuous-wave telephone signals, abbreviated as “voice.”
4. Distance ranges.—The distance between stations over which communication may be established with these radio sets will vary considerably; it will depend on the frequency and the mode of operation, and on topographic, atmospheric, and electrical conditions. In general, approximate reliable ranges of these sets in miles are as follows:
Cw Tone Voice
Both stationary 60 40 20
Both moving , 30 20 15
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SIGNAL CORPS
5. Frequency ranges.—a. The receivers of these sets have a frequency range of 1,500 to 18,000 kilocycles (kc.).
b. The transmitters have a frequency range of 1,500 to 4,500 kc. When the component transmitter tuning unit TU-5-A is employed, the frequency range is 1,500 to 3,000 kc. When transmitter tuning unit TU-6-A is used, the frequency range is 3,000 to 4,500 kc.
6. Channels.—a. The frequency separation required between stations operating in the same vicinity depends upon several variable factors such as the—
(1) Distance between transmitting and receiving stations.
(2) Selectivity of the receivers with which the transmitter is likely to interfere.
(3) Frequency and mode of transmission.
(4) Nature of terrain.
b. In general, a separation equivalent to approximately one percent of the highest frequency employed is practical. Approximately 75 channels with a 40 kc. separation are available, providing sets adjacent in frequency are not closer than a few miles.
7. Use.—Radio sets SCR-193-A, SCR-193-B, SCR-193-C, SCR-193-D, and SCR-193-E may be used in two-way net communication with the same set or other types of transmitting radio sets listed in the left-hand column of figure 1, provided all radio sets used are within the maximum distance range of the least powerful set. Figure 1 shows the frequency bands of radio transmitters which are a component of each of the listed sets and the bands of the other types of radio sets which overlap them. Authorized frequencies which lie within the overlapping bands may be selected for such communication.
8. Transport.—a. Each vehicle named in paragraph 1 is prepared during manufacture with all the necessary mounting holes and many of the fittings required for radio installation. The ignition system is shielded, a 12-volt, 180-ampere-hour storage battery is installed, and a 50-ampere generator is employed in the vehicle to maintain the charge of the battery. For information relative to the installation of these sets, see paragraph 22.
b. All set components are designed for vehicular use. Suitable shock mountings are provided to prevent damage from excessive shock or vibration.
9. Supply.—These sets are not stocked as complete units but are made up from component parts which are requisitioned, stored, and issued separately. While the Signal Corps General Catalog is controlling in regard to these component parts, they are indicated in this manual for information.
4
TM 11-373
9
RADIO SETS SCR—193—A, ETC.
Tuning Unit TU-5A Tuning Unit TU-6-A 1500 2000 2500 3000 3500 4000 4500
scp-
73/
161
163
LEGEND:
I = Transmitter < = Receiver
7/////////////
163A
171 177 & 177A
179
AA-183 AC-183& AD-183
AE-183
AG-183 & A D-1 83 A A-185 & AB-185
AA-187~\ AB-1878 AC-187
187A
'7/0077/
\'07////77/\
\i* >!$5
1138
1165
1167
1120} 1155\p 1163} '
1169
1170-
Spare fuses
0l36 \1137
T \1140 ¥-1149 ^—1181 ¥-1157 ¥—1150 6-1113
1156
WT“'
1115
1116
TL-22Z?
Figure 4. —Radio transmitter BC-191-A, rear view, shields removed.
13. Radio receivers BC-312 and BC-312-C (figs. 5 and 6).—The radio receiver is contained in a metal cabinet. The circuit elements are mounted on a metal front panel and chassis assembly which is entirely removable from the cabinet. This assembly is secured in the cabinet by five panel lock knobs on the front panel and may be removed by turning the panel lock knobs in a counterclockwise direction. The cabinet has four snap-slide catches at the bottom which secure it on four rubber shock elements of mounting FT-162. Rubber shock mounting FT-178 is fastened to the vehicle and to the side of the cabinet to provide additional support for the receiver. Fuses FU-21, lamp LM-27, and mounting FT-162 are included as parts of the receiver.
14. Control box BC-321 (fig. 7).—This control box consists of a metal box rigidly secured to the vehicle by means of a metal bracket. Removal of the two volume control knobs and four screws on the front plate provides access to the interior elements of the box.
15. Radio control box BC-309 (fig. 8).—This control box consists of a metal box rigidly secured to the vehicle by means of four
10
TM 11-273
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RADIO SETS SCR-19 3-A, ETC.
L0CK I’T^'^'^). V^/w\\ \w\ ill / ' WC^M y3^'K\ £■ LOCK
___ X AL1GH TO v=^\\\\\ \\\A //// //m^T ^/crystal* E"iv M
7^hs“ B^==== H H Q '
SIGNAL CORPS U.S. ARMY HEATERS DYN-FIL jpmrRn. .
81W \ RAOI° RECE,VER BC‘312 zi?3553^^ -MVC X-\ / \
I \u °° FOCT MOM*WUIR MEWJWStr
x”—\ N,CR0 ) I II I
1 SzJ —J (J
^3 O ® e Ate
NOISE ADJUST' SEND'£§>7'REC \ X^Z
@® 0 ®SPAM hsarvO
i-cock z5«iit\ 0 yj^jy 0 ।
NOISE BALANCE |Q^j)]LOCK ________________________I
............. —\
oMx........° ° --Q—BJ
. / ' TL-1S35
Figure 5.—Radio receiver B 0-312, front view.
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TM 11-273
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SIGNAL CORPS
screws through the rear plate. Removal of the four screws in the sides of the box near the base provides access to the interior elements.
16. Dynamotor units BD-77-A and BD-77-B (fig. 9).—Each of these units consists of a dynamotor upon which is mounted a metal relay fuse box. The base of the unit is provided with four snap-slide catches for securing the unit to the mounting FT-107. Sockets and a ^6 inch diameter conduit hole in the left-side panel of the relay fuse box provide for power input leads. Releasing the four snap slide catches on the top of the relay fuse box permits removal of the cover and gives access to circuit elements within the box (fig. 10). The required fuses and the mounting FT-107 are included as parts of the dynamotor unit.
12
TL-zaes
Figure 6.—Radio receiver BC-312, chassis rear view.
TM 11-273
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RADIO SETS SCR—19 3—A, ETC.
17. Mast sections MS-49 to MS-53, and mast base MP-37 (fig. 11).—The five mast sections are made of high tensile-strength flexible steel. Mast section MS-49 forms the top of the antenna
i
---------------------------'T I
ON OFF I
PHONE NO I MLC PHONJ^NO 2
<®> ®> gl
© BC-321 © !
m R gJ
© K ' —■/(§)
NOi N02
(VOLUME CONTROL,
TL=1837
Figure 7—Control box BC-321, front and top view.
when all sections are used and the others follow in sequence of their type numbers. Mast section MS-53 screws into mast base MP-37,
/ / .............
w
c'-d®'8‘F.
I .- L/’ flib
■ > Xg r iCW . " ■
• TL-222?
Figure 8. —Radio control box BC-309.
which is rigidly secured to the vehicle. A large helical spring in the mast base provides additional flexibility to the antenna. The upper end of mast section MS-49 terminates in a blunt point. The lower
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TM 11-273
17-18
SIGNAL CORPS
end of each mast section is fitted with a serrated shank and screw for engaging the threaded upper ends of the next mast sections. Ends which are joined in assembling have enamel marks of the same color.
■
Figure 9. —Dynamotor unit BD-77-A.
The body of each section is enameled black and bears the type number at the lower end. The over-all length of the assembled antenna is 15% feet.
Condu/t ho/e for Power Input feuds
Fu-22 X.
1604. FiH3 \ V
\ \
Bhk " rsc ' ■■.XsfU V /
®R.. fc. ax- xWb® - -moi
I "X
W HlnAM/*«■ »- ^.liawr C* r •-
-f . ^160
1602
TL-2?25
2608, Fu-18
Figure 10. —Relay fuse box for dynamotor BD-77-A.
18. Case CS-48, and boxes BX- 8, BX-19, and BX-21.—Case
CS-48 is a metal container into which either one of the transmitter
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TM 11-273
18-19
RADIO SETS SCR-193-A, ETC.
tuning units may be inserted and mounted or carried. The tuning unit is secured in the case by the same four snap-slide catches that are used to secure the unit in the transmitter. Boxes BX-8 and BX-19 carry spare tubes for the transmitter and spare tubes for the receiver, respectively. Box BX-21 carries spare parts, and the microphone, key, and headsets when not in use. These boxes may be rigidly fastened inside the vehicle.
Mast Base MP-37
Mast Sections
MSM9. SO, St, S2 <& S3
TL-I884A
Figure 11.—Mast base and mast sections.
19. Covers BG-67, BG-75, BG-78, BG-79, BG-84, and rolls BG-56, BG-56-A, and cabinet CH-60.—a. Covers.—Cover BG-67 is made of black canvas duck and is placed over the mast base MP-37 when the antenna is not in use. It is secured to the mast base by a leather strap fastened at the bottom of the cover. Covers BG-75, BG-78, and BG-79 are made of heavy waterproofed canvas duck and protect the receiver, transmitter, and dynamotor unit, respectively. Slide fasteners on the fronts of covers BG-75 and BG-78 may be opened to provide access to the front panels of the receiver and transmitter, and the flaps released by opening the slide fasteners may be held back by snap fasteners on the tops of the covers. Openings on the sides of the latter three covers permit the entry of connecting cords to the components within. The preparation of scout car M3A1 by the Ordnance Department for the installation of radio set SCR-193-D includes the installation of a cabinet 42% inches long, 25% inches high, and 10% inches deep. The front of this cabinet is covered by cover BG-84. This cover is permanently fastened to the top of the cabinet. When the radio set SCR—193—D is not in service, the cover is secured over the front of the cabinet by dot fasteners. When the radio set SCR-193-D is to be in service, the front of cover BG-84 is rolled upward and secured in place by three webbing elements which are snapped over the cover by means of suitably positioned snap fasteners.
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TM 11-273
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SIGNAL CORPS
b. Rolls.—Rolls BG-56 and BG-56-A are made of black canvas duck and each holds two sets of five mast sections each in separate
RADIO RECEIVER 8C-3I2 RADIO TRANSMITTER 6C-I9I-A
MOUNTING FT-182 W MOUNTING FT-I5I-8 SNlCtD FOR RADIO SET J-L MAST BASE MR-37
■ / --- ' / - _ M-'M SCR-193-A
ADAPTER-/ MICROPHONE T-17 9— -ADAPTER \
FT-I77-A I \ / I | . -m II * 3 * * * * —. [■( FT-I77-A \ L-Lr, iy’ ‘
OfV Cy C/ *----> *-- '-> *9 A y-*“US£ MA3T SHtELD MP-JJ
f —s P l!» rr.g: m j© j ________________________
19a°.«Q2Fi 1 • ,o«^tr । . K
r n^— 1 A
a * cfc A J « A ___ “"All
I W-*---------------------—J p । j~L
II [f g? 4 ....tajlkr""
TERMI NAU BOX ) UNIT 80-77-A
• / MOUNTING FT-10?
,__' hr g X- A
ty. to i2 VOLT battery
jKjl ______________________________
_ _______CARS USED ON
I O O LICHT TANK COMBAT CAR !j I
« - \\ M 2 A 3 M I AI
I F\ ZV/) 1 roR roR I
Hl S \ // RADIO SE? RADIO SET
\ ______________ SCR-I93-A SCR-I93-C__ll
CONTROU BOX BC-321 WHERE USED TYPE LENGTH TYPE LENGTH
HEADSET P-lt O " ’ ——
(a) BC-ISI-A TO TER BOX CD-359 24 IN CO-359 24 IN
(V) BC-lBt-A TO TER BOX CD-268 24 IN CO-288 24 IN
Am ® BC-I9I-A TO BD-77-A CO-221 30 IN CD-221 SOIN.
() X. ® BC-**’-A T0 BD-77-A CD-205 30 IN CD-205 30 IN
/| (('JFl microphone th? z-\ ———————————————————— '
I! \Sy &O3'2 To JUNCTION BOX CD-269 SOIN CD-269 30 IN
X. J CD 60"77-A TO TER BOX C0-I65-A 18 IN C0 I6S-A 18 IN
/ (V) BC-312 TO JUNCTION BOA CO-314 30 IN CO-314 30 IN
TlCAOSCT P-19 Q7) B0-I9I-A TO BC-312 CO-261 108 IN CO-261 108 IN.
I I I . I 1 I I I 1 TL-2226
Figure 12.—Radio sets SCR-193-A and SCR-193-C, cording diagram.
compartments. The opening on one end and along the side is closed by suitable fasteners.
16
TM 11-273
19
RADIO SETS SCR—193—A, ETC.
c. Cabinet CH-60.—The cabinet CH-60 is 53% inches long, 29% inches high, and 11% inches deep and is divided by one vertical parti-
ADAPTER -------
FT-I77-A—-ET--T
ZMHBBMBHHBaHBBBMlllIHlia. I XST’.T.'.'iw::vxr.z<; p op ci
MICROPHONE T-17 I JZa 3“
Is C®°O:%"| f Vz "f I -•• HEZL.., f « © J__________ ) I If SVoSUT J, K/SsZ —
6 (J I-----J O O£W ------1......... ( " ° ks^xf INSULATOR
O I TERMINAL RADIO TRANSMITTER BC-I9I-A »N-90
O______Q O X Al BOX MOUNTING FT-I5I-B
j?S , ,... o o r—^--vibun X t
IO RECEIVER BC-312 I O M
MOUNTING FT-162 I PL-H4 -----nj rn— Y\ M
J I----(h) M M Q ^JACASARE PROVIDED TO ACCOMODATE
^■■■■■■■■■■■^ ■■■■■■■^^^ I □ ’& : juT^ •-MICROPHONE T-17, I-HEADSET P-19.
,—n ■ —ft-Jf______< AN0 •"LOUDSPEAKER LS-3 IF DESIRED
® v Oh V
_J VJr""*CONTROL BOX BC-321
PL-SSs/'p^^%,S .. (£)
K--------------1--------------
Y \\ / /% RADIO CONTROL BOX BC-3OB
HEADSET P-19
DYNAMOTOR UNIT BD-77-A
MOUNTING FT-IO7
CARS USED ON
SCOUT CAR
M 3
FOR |
RADIO SET
SCR-173-8
WHERE USED TYPE LENGTH
(a^) BC-I9I-A TO BC-312 CO-262 144 IN |
(V) BC-I9I-A TO B0-77-A CD-292 3« IN. ll
(CJ BC-I9I-A TO BD-77-A CD-206 36 IN.
(□J BC-I9I-A TO TERM BOX. CD-358 30 IN
(T) BC-I9I-A TO TERM BOX. CD-290 30 IN
(7) BC-312 TO TERM BOX. CD-297 9« IN. |! ‘
(7) BC-312 TO TERM BOX. CD-277 96 IN
(7) BD-77-A TO TERM BOX. CO-I75-A 48 IN I "
(7) BC-309 TO TERM BOX CD-295 90 IN {
I I I | | I I | I TL-2227
Figure 13.—Radio set SCR-193-B, cording diagram.
s
tion and one horizontal shelf, the latter in the right portion of the cabinet, so as to form three compartments. The cabinet CH-60 has
296642°—41---2
17
TM 11-273
19-20
SIGNAL CORPS
two doors similarly constructed, one covering the left compartment and the other the right compartments. The doors are hinged above their center lines so that the top portion swings outward and downward to lay against the lower portion. In this position, the doors are removable from the cabinet frame by a vertical movement of the door assembly. This vertical movement disengages offset brackets, welded to
—MAST SECTIONS .—Al
MS AS TO MSS3 ZZ
XIIJ-IS [ | TTMICROPMONC T-/7 .Z'AT \\
cover sc-er (T&ALTL 11
L I' 'll
msr S3 ST MP 37_ I [ I zZ
I £wire n~lze
i p’M ^locate *■ Mill rv* //v ASitvtacri / ~ I
1 ------[ K 'E~/ -INSULATOR IN-IOI //MOUNTING /
' L RADIO RECDIVER 0C-3I2-C rT ,7£ / I
I 1SL..Z MOUNTING FT-/6Z 2 \ I
AATs/AAur -Zr|^| f ~ MATT ' — jj ।
COVDR BO 7S—!■ /f/\ iNZS'fL.l&'GDIO TRANSMITTER BC-I9I-C '
If_I) f- MOUNTING FT-I5I-& c_//// U |
I '“"“'"^L,____ PL-H4 c scI I
I r^, V-ywr put c___4 » J JI |
I ■■■»■ Xa ■ a-- -a i* • Z I ।
COVER BC-84-P /,/z-^s---5Z-z | ~~ ~~~ 1 -----L—----- I I
; n~ ® *©o© @□< 11
CoppRee.73-^^_____________ □r^T ? i----------------------------wr xA 11
1 \( rl 'J M
7 CREEtl-IC. I 6 HAEURAL L3 0 O O » 6 A
6 RED-16 K 7 RED-IB t | SHIELD-IB B GREEN-IO
» SHIELD-13 “ ‘
BLACK-IB ---------------------------- 'I PARTIAL V/CLA SNOL/ING TERMINAL T L~ 2228--------------BLOCK AND CONNECTIONS ON RIGHT
Side or transhmtte^
Figure 14.—Radio set SCR-193-D, cording diagram.
the bottom of the door assemblies, which engage a portion of the cabinet CH-60 frame when the doors are in place.
20. Vehicular accessories.—a. A junction box (fig. 12) is installed in light tank M2 A3 and combat car Ml Al by the Ordnance Department to facilitate making of connections for the radio set SCR-193-A and SCR-193-C. In it are mounted terminal block TM-183, potentiometer RS-218, and jack JK-34-A.
b. A car terminal ,box (figs. 12, 13, 14, and 15) is installed during manufacture in each vehicle named in paragraph 1. In it are mounted
18
TM 11-273
20
RADIO SETS SCR-193-A, ETC.
OMAST SECTIONS
,-CF~|=. fl MS -49 TO MS-53
____________KET_U45_______ MICROPHONE T-17 I—1
SIG ANT.gX, ✓ ~^S>ST BASE MP-3?
ALT ANT Z\_rO) ) . I > ,
(32h°' *u0 f / ! 1
qgno A o headset p-,9 r A.'.rp.'y-y;^,
T (/ U L ant • 3_* C»S£ gtc a to J
RAO ^RECEIVER BC-3I2 ( ------
— CD-4lt(66) PL-S6H^ PL-S59 »»st sections
ZZ Z*\ XS-UTO MS-SS. I \ CO ls,
(O) \ .MOUNTING
CD-359(24) XV A \ .antes.. /-«ut.To.
\ / / / ■-»_____________________
pi - "4ST Ml l/S7> 11^/ ® i$i 0 Hi— =Bil-P.T.'ll?
PL MF* 37 r» ------------- RA0,° ',rcC'VEr’ »
Sod RAO.O TRANSMlTTtB 8C-3I2-C
A/1TEMHA SUPPORT^ ; 8C-.9I-C MOUNTS P T - .62
r'”»nrij pi:; । hi| (i)sc-o-444 2 / , mounting rr>tsi>» . ,
/ / C 07NAMOTOR UNIT
f—_____________ 1^ T3 CD-440(48")—— CD-226(48") neXncw plate//'' 7?-=^
I ® SC-0-4..E / I I / '
’no”’ TN0W COLOR TCNminalbot-/ __3^====^ __—I T' "
/'I YELLOW-20 p YELLOW-18 RADIO TRANSMITTER ' m-
2 NATURAL-12 3, BLUE-18 BC-I9I-C /V--------~~~>-------------“--------
3 BLUE-20 6 NATURAL-18 ' /r«o.< Tloon/
X 4 BLACK-12 K 7 RE0-I8 -- ------- -- c»-ito-»
7 GREEN-16 8 GREEN-18
8 REO-16 10 SHIEL0-I8 .
1.10 SHIELO-18 LlO BLACK-IS PL-S59 \J7/ ( P*-'S6I NOTE'
„ Z-~p -CCC ANTENNA ANO GROUND CON-
NECTIONS SHALL BE MADE WITH
4] / X WIRE W-128.
/ \ ENDS OF WIRE W-128,AFTER
I T T ] / \ BEING CUT TO PROPER LENGTH,
I I SHALL BE TINNED FOR CONNECT-
----- I ING AT BINDING POSTS ANO GROUND
------------1------1 1 I--- \ / CONNECTIONS.
TERMINAL BOX | \ /
I TO BATTERY /^Z^^
t,_________ C0-l70-A(60"> 4 .A1 ■... . a I TL-^^OO
DYNAMOTOR UNIT BD-77-B I L ZZZy
Figure 15.—Radio set SCR-193-E, cording diagram.
a terminal block for storage battery connections and brackets for the installation of terminal block TM-183. The terminal box is connected to the junction box (where used) by conduit (fig. 12).
19
TM 11-273
21
SIGNAL CORPS
Section II
EMPLOYMENT
Paragraph
Limitations_______________________________________________- _ ______ 21
Installation____________________________________________________________ _ 22
Check and adjustments prior to operation__________________________________ 23
Operation in general______________________________________________________ 24
Transmitting______________________________________________________________ 25
Receiving_________________________________________________________________ 26
Care and adjustments____________________________________________________ 27
Storage------------------------------------------------------------------- 28
21. Limitations. These sets have the usual limitations possessed by any radio set of the same power, mobility, and frequency range. The distance ranges (par. 4) and the channels (par. 6) must be considered approximations which are affected by many factors, the majority of which cannot be controlled by the user of the set. Some of the factors which are controllable are listed below and require the attention of the user if the sets are to operate most effectively.
a. Distance range.—(1) All other things being equal, distance range is increased by—
(a) Keeping the equipment in perfect condition through frequent inspection and correction of all defects. For inspection procedure, see paragraph 33.
(6) Using c. w. in preference to tone, and either c. w. or tone in preference to voice.
(c) Accurately tuning the transmitter and receiver.
(t2vous^rTO~Q~Q~Q T)~terQ ic;
tl-zzjo
Figure 16.—Filament-resistor connection board.
14V row of studs directly under it for the studs used in operation (8) above, but start at the extreme right end of the MOD FILAMENT row.
(10) Set the CW FIL MOD FIL switch on CW FIL and the TONE CW VOICE switch on VOICE. Place the OFF ON switch in the ON position. The CW FILAMENT voltage will now be less than 10 volts. In the same manner as in (8) above, starting with the first stud to the right of the connection made in (8) above and successively moving to the right, connect pairs of studs on the COMP and CW rows until a pair is found which causes the filament voltmeter to read 10.5 volts. Turn the OFF ON switch to the OFF position. Connect a link between the studs just located.
23
TM 11-273
23-24 SIGNAL CORPS
(11) Shut the motor of the vehicle off and place the 12V 14.2V switch in the 12V position.
(12) Set the TONE CW VOICE switch on CW and the CW FIL MOD FIL switch on CW FIL.
(13) Place the transmitter OFF ON switch in the ON position,* and allow the battery voltage to fall to a steady value. The filament voltage will now be found to be less than 10.5 volts. With a screwdriver or a short piece of copper wire (No. 12 B&S or larger), starting at the extreme right end of the CW FILAMENT row, successively connect between a stud on the CW FILAMENT row the 12V row directly under it, until a connection is found that causes the filament voltmeter to read 10.5 volts. Place the OFF ON switch in the OFF position, and connect the long link provided between the pair of studs just located.
(14) Set the TONE CW VOICE switch on TONE and the CW FIL MOD FIL switch on MOD FIL. Place the OFF ON switch in the ON position.
(15) Starting with the left end of the MOD FILAMENT row, in the manner indicated above, successively move to the right until a pair of studs on the MOD FILAMENT row and the 12V row are found that will cause the filament voltmeter to read 10.5 volts. Place the OFF ON switch in the OFF position. Connect the long link provided between the pair of studs just located.
(16) Place the 12V 14.2V switch in the 14.2V position. When it is certain that the dynamotor has stopped, replace the tube compartment shield and replace the plugs PL-59 in the dynamotor and transmitter sockets. The filament voltage has now been adjusted so that under actual operating conditions, the voltage at the tube filament connections will be 10 volts under all conditions of operation.
c. Special adjustments.—When necessary, special adjustments are made as prescribed in paragraph 35.
24. Operation in general.—a. Interference.—(1) Interference is minimized by c. w. operation and by the use of the crystal filter.
(2) Power lines may contribute a source of interference, particularly at the higher frequencies. Avoid operation in the vicinity of power lines.
(3) A form of interference, called track static, may be generated by track laying vehicles. This form of interference must be cured at the source.
(4) A form of interference due to improper joining of metal parts of the vehicle may be prevented by care in grounding the radio equipment and carefully bonding together (connecting) all metal parts of the vehicle.
24
TM 11-273
RADIO SETS SCR—193—A, ETC. 24
(5) In moving vehicles, vibration may cause the thermostats in the receiver BC-312 to produce noise, in which case the heaters should be turned off.
(6) The above forms of interference, and others which may be noted after some experience, may usually be identified by their characteristic noises.
b. Net operation.—If net operation is prescribed, each set in the net must be accurately tuned to the same frequency. Frequency adjustment is best accomplished with the aid of a frequency meter. Tune all sets within the same net under substantially the same conditions. The position and the length of the antenna, the temperature, and the battery terminal voltages must be fairly uniform. Avoid tuning in the immediate vicinity of buildings and metal structures. If operation in transit is to be effected, tune sets with engines of the vehicles running. Lock all transmitter controls after the net tuning operation.
c. Methods of operation.—(1) Always operate the transmitter with the antenna tuned. This is particularly important in net operation in order to maintain the correct frequency. Tone transmission, being broad, is well adapted to net operation, but produces more interference to nearby radio sets than does c. w. transmission. Voice transmission produces more interference than does tone transmission.
(2) For satisfactory net operation, and to insure that the receiver stays on net frequency, turn the HEATERS OFF ON switch of radio receiver BC—312 to the ON position for 15 to 30 minutes prior to operation, and leave it in that position during operation.
(3) So that the receiver will not be too selective during stand-by periods, turn the CRYSTAL PHASING control, which controls the use of the crystal filter, to the OUT position.
d. Precautions.—(1) Controls.-—Observe care in handling all of the controls. Most of them are equipped with stops to limit their movement. Forcing a control beyond its normal stop will seriously damage the equipment. This caution applies particularly in the receiver to controls marked VERNIER, CRYSTAL PHASING, and VOL.
(2) Serial numbers.—The serial numbers of transmitter tuning units must be identical with the serial number of the transmitter with which used. Do not interchange transmitter tuning units with those of other transmitters.
(3) Vacuum tubes.—A marked decrease in the life of the transmitter vacuum tubes results from over or under voltage applied to the filaments. Check the filament voltage frequently and adjust, if necessary, as prescribed in paragraph 23.
(4) Band change.—In changing the frequency band of the receiver it is possible to stop the BAND CHANGE switch between two
25
TM 11-273
24-25
SIGNAL CORPS
settings. Turn this switch until it definitely engages the desired band.
(5) Receiver power cord.—Avoid undue pulling or stressing of this cord. Disconnect the cord from the receiver before the receiver panel and chassis assembly is removed from the cabinet. At no time apply power to the receiver while the panel and chassis assembly is being handled.
(6) SEND REC switch.—When the set is not being used during actual transmission periods, place the SEND REC switch in the REC position. If left in the SEND position, there is a small current drain on the battery.
25. Transmitting.—a. Controls (figs. 2, 3, 5, 7, and 8).—Transmission is accomplished or controlled by the following:
(1) Dynamotor unit BD-77-A (SCR-193-A, SCR-193-B, SCR-193-C).
(2) Dynamotor unit BD-77-B (SCR-193-D, SCR-193-E).
(3) At control box BC-321 (SCR-193-A, SCR-193-B, SCR-193-C).
(a) OFF ON switch.
(6) MICRO jack and microphone T-17 connected thereto for voice transmission.
(c) MICRO jack and key J-45 connected thereto for c. w. transmission (SCR-193-B only).
(4) At radio control box BC-309 (SCR-193-B).
(a) OFF ON switch.
(6) KEY jack and key J-45 connected thereto for c. w. transmission.
(5) On radio receiver BC-312, BC-312-C.
(a) KEY and MICRO jacks and a key and microphone for c. w. and tone, or voice, respectively, connected thereto.
(6) SEND REC switch.
(c) Cord F (see fig. 13) to conduct audio frequencies through the circuits of the terminal box to control box BC-321.
(6) On radio transmitter BC-191-A, BC-191-C or connected to it.
(a) An antenna described in paragraph 17 connected to the ANT binding post of the output terminal strip. This strip may be installed as outlined in paragraph 12.
(6) A thermocouple type, 0 to 8 ampere, radio frequency ammeter marked ANT CURRENT located in the upper right-hand corner of the front panel. This meter indicates the current output of the transmitter.
(c) An antenna inductance tuning dial, marked ANT IND TUNING, M, used for inductively tuning the antenna. It is located immediately below the antenna current ammeter.
(d) An antenna circuit switch, marked ANT CIRCUIT SWITCH, N, used to accomplish the antenna circuit changes required for tuning
26
TM 11-273
25
RA'DIO SETS SCR-19 3—A, ETC.
the transmitter into various types of antennas. It is located directly below the antenna inductance tuning dial.
(g) An antenna capacity tuning dial, marked ANT CAP TUNING, O, located immediately below the antenna circuit switch. This control is used to adjust or tune a capacitor in the antenna circuit. It is provided with a locking mechanism so that its final position may be maintained.
(f) An antenna inductance switch, marked ANT IND SWITCH, P, used for obtaining large variations in antenna inductive loading. This switch is a 5-position switch, each position corresponding to a stop on the inductance coil and is located in the lower right-hand corner of the front panel.
() If after tuning the antenna as above, the TOTAL PL CURRENT meter reads less than 200 milliamperes, the coupling to the antenna may be increased by placing the ANT COUPLING SWITCH, D, on a higher numbered point and the antenna circuit retuned as indicated above. When finally adjusted, the total plate current should not exceed 200 milliamperes.
(2) The modulator bias adjustment.—Having completed the procedure directed in (1) above—
(a) Note the value of total plate current when the transmitter is tuned for c. w. operation.
(Z>) Move the transmitter OFF ON switch to the OFF position.
(c) Place the TONE CW VOICE switch on the VOICE position.
(d) Move the transmitter OFF ON switch to the ON position.
(e) Press the TEST KEY, located to the left center of the transmitter panel, and note the current indicated on the TOTAL PL CURRENT meter. The total plate current meter should now read a current 20 ma. greater than the current noted in (a) above, as the modulator tubes are now drawing about 20 ma. (One small scale division of the TOTAL PL CURRENT meter is equivalent to a 20 ma. current change.) In event that the current change is greater or less than 20 ma., the control labeled MOD BIAS will need adjustment. (The dial on this control is so calibrated that the current drawn by the modulator tubes is inversely proportional to the setting of the dial.) The dial is rotated by using a screw driver inserted in the dial rotating device located just to the left of the MOD BIAS control (fig. 3). Proceed with the adjustment as follows:
(f) Release the TEST KEY.
(g) Move the transmitter OFF ON switch to the OFF position.
(A) Remove the tube compartment shield.
29
TM 11-273
25
SIGNAL CORPS
(i) By successive small steps, and the procedure indicated in (a) to (g), inclusive above, rotate the MOD BIAS control in a direction so as to bring the modulator plate current to the value indicated in (e) above.
Caution.—Changing vehicular battery voltage will cause a change in the total plate current drawn on c. w., and frequent checking of the value of total plate current on c. w. during the progress of the above adjustment is necessary.
(3) For voice operation.—With the adjustment of the MOD BIAS control completed, the adjustment of the INPUT LEVEL control is next in order. This adjustment will require the use of an additional radio set suitable to send and receive transmissions in the frequency range of the radio set SCR-193-A. This additional radio set should be located at a sufficient distance and/or operated with a reduced receiving antenna such that the receiver circuits are not overloaded by the signal strength of the transmissions from the SCR-193-A. The adjustment is accomplished as follows:
(a) Release the TEST KEY.
(6) Set the transmitter BC-191-A OFF ON switch in the OFF position.
(c) Insert the plug for the microphone in the MICRO jack.
(d) Set the SEND REC switch located on the receiver panel to the SEND position.
(e) Set the OFF ON switch located on the receiver panel in the ON position.
(/) Remove the tube compartment shield and using a screw driver inserted in the dial rotating device located to the left of the INPUT LEVEL control (fig. 3), set the dial at 1.
(g) Set the transmitter OFF ON switch to the ON position.
(A) Depress the microphone button, and using a standard speech input to the microphone, conduct a transmission to the distant radio station mentioned above. (These transmissions should be of about 30 to 45 seconds duration in order that the distant operator may judge the quality of the speech transmission.)
(i) Obtain a report as to signal strength and degree of modulation.
(J) By successive small steps, rotate the INPUT LEVEL control to higher numbered positions, by the procedure directed in (a) to (i), inclusive above, until the distant station makes a report of indistinct transmission.
(E) Reduce the setting on the INPUT LEVEL control somewhat and obtain a report from the distant station. The transmissions should now be clear and distinct.
30
TM 11-273
RADIO SETS SCR—19 3—A, ETC. 25-26
(I) Note the value of total plate current during the transmission conducted in (A?) above. This should never exceed 300 ma. Under very noisy vehicular conditions, it will be necessary to set the INPUT LEVEL control at a much lower point than that arrived at in (A?) above, and raise the speech level to the microphone until the current noted above is obtained. The speech level to the microphone is raised by talking in a loud voice with the microphone touching the lips. Setting the INPUT LEVEL control too high results in overmodulation with indistinct transmissions, abnormally wide side bands with the consequent increase in interference on adjacent channels, overloading of power sources, blowing of fuses, and damage to the equipment.
(4) For tone operation.—Having completed the procedure directed in (1) and (2) above—
(a) Move the transmitter OFF ON switch to the OFF position.
(6) Place the TONE CW VOICE switch on the TONE position.
(c) Move the transmitter OFF ON switch to the ON position.
(d) Tone modulation may be effected by using the microphone button, transmitting key, or TEST KEY. The total plate cun-ent reading will be between 300 and 350 milliamperes.
(5) Side tone adjustment.—The magnitude of transmitter side tone delivered to the output circuit of the radio receiver is adjusted by means of the stepwise control, marked SIDE TONE, located in the tube compartment. (See fig. 3.) In the junction box TM-188, SCR-193-A and SCR-193-C, there is located a potentiometer RS-218 which provides for additional adjustment of the side tone.
26. Receiving.—a. Controls (figs. 5 and 7).—Reception is accomplished or controlled by the following:
(1) On the receiver BC-312, BC-312-C or connected to it—
(a) A 6-position switch located on the left center of the front panel marked BAND CHANGE. Each position is marked with the limiting frequencies-in kilocycles of the band through which the receiver can be tuned. (See par. 31.) The BAND CHANGE switch also operates a masking plate in front of the main tuning dial.
(6) A flat disk main tuning dial located in the upper left of the front panel behind a windowed reflector and marked FREQUENCY. The dial has seven concentric scales, the outer six of which are calibrated directly in frequency. The first or inner scale is calibrated in equal division from 0 to 45 for ready position reference. The masking plate referred to in (a) above covers the frequency scales not in active use so that only the 0 to 45 scale and that pertaining to the frequency band selected by the BAND CHANGE switch may be read.
31
TM 11-273
26
SIGNAL CORPS
(c) Two controls on the right center of the front panel marked FAST TUNING and VERNIER, respectively. The FAST TUNING control rotates the main tuning dial at a reduction ratio of 25 to 1. The VERNIER control rotates the main tuning dial at a reduction ratio of 90 to 1. A calibration of 100 equal divisions around the periphery of the VERNIER control permits interpolation of the inner 0 to 45 scale of the main tuning dial. The VERNIER control makes one complete revolution to move the main tuning dial one graduation on the 0 to 45 scale.
(d) An antenna tuning control to the.left of the main tuning dial marked ALIGN INPUT.
(e) A crystal filter control to the right of the main tuning dial marked CRYSTAL PHASING. An arrow on the control when the latter is rotated to the OUT marking on the panel indicates that the crystal filter is out of the receiver circuit. Other positions of the arrow indicate that the crystal filter is in the circuit. (See par. 31e and fig. 29.)
(/) A volume control to the right of the CRYSTAL PHASING control. It is marked VOL and has 100 equal divisions marked on its periphery for ready position reference. An arrow marking on the control indicates the direction of rotation for increasing volume. This control is effective for manually changing the volume when the OFF MVC A VC switch is in either the MVC or A VC position.
0) A two-way toggle switch marked CW OSC OFF ON located to the right of the VOL control.
(A) A CW OSC ADJUST control located in the upper right-hand corner of the front panel.
(f) A 3-position switch in the lower right of the front panel marked OFF MVC AVC, respectively, for each position. When the arrow on this switch points to OFF, power is removed from the receiver. When it points to MVC, the receiver is turned on and manual volume control of the receiver is provided. When it points to AVC, the receiver is turned on and automatic volume control of the receiver is provided. See paragraph 31? for the detailed manner in which the OFF MVC AVC and VOL controls jointly function.
0’) A two-way toggle switch in the lower right of the front panel marked SEND REC.
(&) Two small knob controls located below the BAND CHANGE switch, marked NOISE ADJUST and NOISE BALANCE, respectively.
(Z) A two-way toggle switch located in the right center of the front panel, marked HEATERS OFF ON (radio receiver BC-312 only).
32
TM 11-273
26
RADIO SETS SCR—193—A, ETC.
(m) Three fuse holders marked FUSE on their screw caps and HEATERS, DYN-FIL, and SPARE, respectively, for the BC-312, and LAMPS, DYN-FIL, and SPARE, respectively, for the BC-312-C, on the panel immediately below. Being identical, the fuses contained within all three holders are interchangeable.
(n) Four terminals SIG ANT, NOISE ANT, GND, respectively, on the left-hand edge of the panel and ALT SIG ANT in the upper right-hand corner of the front panel in radio receiver BC-312. In radio receiver BC-312-C, two terminals are marked SIG ANT, one NOISE ANT, and one GND. They are all located along the left side of the front panel.
(o) Five jacks marked KEY, MICRO, SPEAKER 2ND AUDIO, PHONES 2ND AUDIO, and PHONES 1ST AUDIO, respectively, located on the lower right edge of the front panel. These jacks are provided for the insertion of plugs for a key, microphone, loudspeaker, and headphones, respectively.
(p) A 14-contact socket located on the front panel. Power for the receiver is supplied through a cord plug which is inserted into this socket. The leads from this power socket to the interior of the receiver are accessible upon unscrewing four screws of a protective metal cover above the socket and removing the cover.
(g) A shielded cord for connecting the antenna terminals to the antenna, or to the REC terminal of the transmitter when the latter is used with the receiver.
(r) A noise suppressor antenna, if used, is connected to the NOISE ANT terminal.
(s) A ground wire for grounding the receiver chassis to the chassis of the vehicle is connected to the GND terminal.
(2) On the control box BC-321.
(a) Two jacks located on the bottom marked PHONE NO. 1 and PHONE NO. 2 in which may be inserted plugs for two headsets for remote reception.
(6) Two controls located on the front plate marked VOLUME CONTROL NO. 1 and NO. 2, respectively, for controlling the volume in headphones referred to in (a) above.
b. Procedure.—The receiver may be operated for c. w., tone or voice reception. Volume level is controlled manually alone, or manually and automa tically together. Selectivity may be controlled by the use of the crystal filter in all cases.
(1) For c. w. reception.—(a) Read paragraphs 23 and 24.
(6) For conditions requiring above average frequency stability, move the HEATERS OFF ON switch (BC-312 only) to the ON position 15 to 30 minutes prior to operation.
296642°—41---3
33
TH 11-273
26
SIGNAL CORPS
(c) Insert plugs for headsets P-19 in PHONES 2ND AUDIO jack, or PHONES 1ST AUDIO jack of the receiver; in PHONE NO. 1 and/or PHONE NO. 2 jack of the control box BC-321, if used. Insert plug for loudspeaker, if used, in SPEAKER 2ND AUDIO jack.
(d) Rotate BAND CHANGE switch to the position which covers the assigned frequency.
(e) Move the CW OSC OFF ON switch to the ON position.
(/) Move the CRYSTAL PHASING control to the OUT position.
(gr) Move the SEND REC switch to the REC position if the receiver is not used in conjunction with the transmitter.
(A) Rotate the FREQUENCY or main tuning dial by means of the FAST TUNING control until the assigned frequency is indicated on the dial.
(0 Move the OFF MVC AVC control switch to the MVC position. Receiver output volume is manually controlled when the switch is in this position.
C?) After a brief period of time in which the receiver “warms up”, rotate the ALIGN INPUT control until maximum noise is heard in the headset.
(k) If the signal is weak or slightly off frequency, use the VERNIER control for finer tuning. C. w., tone, or voice signals on the assigned frequency should now be distinguished. It may be necessary to tune on either side of the assigned frequency until the desired signal is located, and/or readjust the ALIGN INPUT control.
(Z) The pitch of the signal may now be further adjusted to a desired note by the CW OSC ADJUST control. The use of the CW OSC ADJUST control permits a 4,000 cycle variation in the resultant beat note of the c. w. signal, but does not change the frequency adjustment or sensitivity of the receiver.
(in) The VOL control may be rotated at any stage of the tuning to adjust the output volume to a desired level. An increase in volume increases the sensitivity of the receiver. In tuning the receiver initially, it is preferable to maintain the volume fairly high. Volume is further adjusted by VOLUME CONTROL NO. l or NO. 2 on the control box BC-321 if the latter is used.
(n) An increase in selectivity of the receiver, if desired, may now be accomplished as prescribed in (4) below. It is inadvisable to employ automatic volume control when receiving c. w. or tone signals.
(2) For tone or voice reception.—Use the same procedure as prescribed for c. w. reception ((1) above) except place the CW OSC OFF ON switch in the OFF position as soon as the signal is tuned in.
(3) For automatic volume control.—Move the OFF MVC AVC switch to the AVC position. While this reduces the sensitivity of the
34
TM 11-273
26-27
RADIO SETS SCR—193—A, ETC.
receiver, it tends to maintain the output at a constant level as determined by the VOL control setting. Automatic volume control is preferable where the voice signal fluctuates or otherwise tends to vary in output level.
(4) For increased selectivity or rejection of interfering signal.—Rotation of the CRYSTAL PHASING control from the OUT position in a counterclockwise direction increases the selectivity of the receiver. Careful adjustment of this control will permit of rejecting or minimizing an interfering signal on an adjacent channel without serious attenuation of the desired signal. Maximum selectivity is, in general, indicated by minimum background noise, and usually is established when the arrow on the CRYSTAL PHASING control is in the vertical position. The crystal filter is intended primarily for use in the reception of c. w. signals. It tends to cut off the sidebands of voice transmissions, but, depending on how far the CRYSTAL PHASING control is advanced, it frequently eliminates interference on adjacent channels without destroying the actual intelligibility of the voice signals. Its best use must be determined by trial.
c. To reduce engine ignition interference on the 1,500-3,000 kc. frequency bands.—(1) Follow the procedure prescribed in 5(1) above, tuning on any frequency in the two frequency bands.
(2) Connect the signal antenna to the SIG ANT terminal; Disconnect the noise antenna. (The noise antenna consists of a piece of shielded wire connected between the source of interference and the NOISE ANT terminal on the receiver.) Adjust the NOISE ADJUST control to receive maximum noise output.
(3) Disconnect the signal antenna. Connect the noise antenna to the NOISE ANT terminal. Adjust the NOISE BALANCE control to receive maximum noise output. The noise output should be equal to that secured in (2) above. If the noise outputs are not equal, relocate the pick-up end of the noise antenna imtil they are equal, and readjust the NOISE BALANCE control for maximum noise output.
(4) Connect both antennas. Adjust both NOISE ADJUST and NOISE BALANCE controls until the minimum noise output is secured.
(5) If noise reduction is unsatisfactory, it may be necessary to move the pick-up end of the noise antenna a number of times, repeating the above procedure each time until the best results are obtained.
27. Care and adjustments.—a. Inspections.—To insure uninterrupted service, inspect the various components of each installation before and after each day’s operation. Make a thorough inspection of each installation after every 50 hours of operation. For inspection instructions, see paragraph 33.
35
TM 11—273
27-29
SIGNAL CORPS
b. Preservation.—(1) At all times when the receiver, transmitter, or dynamotor unit are not in actual operation, place covers BG-75, BG-78, and BG-79 over these components, respectively. Close all slide fasteners. Securely fasten boxes and cases containing the transmitter tuning unit not in use, spare tubes, and other accessories at all times. Remove headsets, keys, and microphones when not in use, and put in a safe place. The antenna may or may not be disassembled, depending on its prospective use. If it is disassembled, insert mast sections in compartments of roll BG-56 and place the latter in a safe place. Screw a bolt provided for the purpose in the top of the mast base and strap cover BG-67 over the whole. To avoid injury due to shock or vibration of the vehicle when in motion, secure or pad all items of these sets which are not otherwise protected.
(2) Cover BG-84 is used on radio set SCR-193-D.
(3) The cabinet CH-60 protects radio set SCR-193-E.
c. Lubrication.—Components of these sets will be lubricated according to instructions outlined in paragraph 34.
d. Special adjustments.—See paragraph 35.
e. (1) In inclement weather.—Where there is a likelihood of exposure of the set components, cover these components as in b above. These sets may be operated with covers on. Slide fasteners on the covers of the receiver and transmitter are opened and the front flaps held up and back by snap fasteners during operation.
(2) Radio set SCR-193-E is not equipped for operation with the doors of cabinet CH-60 in place.
28. Storage.—a. If these sets are to remain out of service but within the vehicles for more than a few days, proceed as directed in paragraph 275. Disassemble the antenna and cover the ends of the mast sections with petroleum jelly before placing in roll BG-56.
b. If set components are to be removed from the vehicle and stored elsewhere, handle them carefully, cover or wrap securely against dust, place in a dry, protected location, and safeguard against accidental injury. Inspect frequently for dust, rust, or injury, and clean and repair if necessary.
Section HI
DETAILED FUNCTIONING OF PARTS
Paragraph Radio transmitters BC-191-A and BC-191-C, and transmitter tuning
units TU-5-A and TU-6-A______________________________________ 29
Dynamotor units BD-77-A and BD-77-B______________________________ 30
Radio receivers BC-312 and BC-312-C_____________________’________ 31
29. Radio transmitters BC-191-A and BC-191-C, and transmitter tuning units TU-5-A and TU-6-A.—The transmitter,
36
TM 11-273
29
RADIO SETS SCR—19 3—A, ETC.
together with either of the transmitter tuning units, contains the circuit elements for c. w., tone, or voice transmission. With transmitter tuning unit TU-5-A, the transmitter covers a frequency range of 1,500 to 3,000 kc. With transmitter tuning unit TU-6-A, it covers a range of 3,000 to 4,500 kc. During the explanation of the detailed functioning of the transmitter, it will be assumed that transmitter tuning unit TU-6-A is being used.
a. General circuit.—The circuits of radio transmitters BC-191-A and BC-191-C are for all practical purposes identical. The radiofrequency circuit is of the master oscillator, power amplifier type. The audio-frequency circuit consists of a push-pull modulator which is driven by an audio amplifier. The transmitter utilizes a tube VT-4-C for the oscillator, a tube VT-4-C for the power amplifier, two tubes VT-4-C in push-pull for the modulator, and a tube VT-25 for the audio amplifier (speech amplifier). (See figs. 17, 18, and 19.) For c. w. transmission, only the master oscillator, power amplifier, and speech amplifier tubes operate. For tone and voice transmission, all tubes operate. The power amplifier operates Class C; the modulator tubes in push-pull operate Class B; the audio amplifier driver tube operates Class A. Sufficient audio-frequency power is obtained from the modulator tubes for plate modulation of the power amplifier (tone or voice transmission). Side tone, for monitoring purposes is supplied to the receiver from the speech amplifier during c. w., tone, and voice transmission.
b. Oscillator circuit.—The master oscillator circuit is schematically illustrated in figure 22. The oscillatory circuit by which the frequency of the transmitter is controlled is contained in the transmitter tuning unit TU-5-A or TU-6-A, as the case may be. When the transmitter tuning unit TU-6-A is employed and the BAND CHANGE SWITCH, A, is in position 2 (fig. 21), the oscillatory circuit comprises the tapped coil 601 and the variable capacitor 607. Moving the BAND CHANGE SWITCH to position 1 places the fixed capacitors 603 and 613 in parallel with the variable capacitor 607 and enables this tuning unit to cover the lower ranges of its frequency band. Continuous adjustment of frequency is accomplished by means of the variable capacitor 607, control B (fig. 22). Controls, coil, and capacitors of transmitter tuning unit TU-5-A (fig. 20) are arranged for similar operation on four bands, all of which are lower in frequency than those obtained with transmitter tuning unit TU-6-A. In each tuning unit, both coil and capacitors are thermally compensated to reduce frequency variation due to any change in ambient temperature. Subsequent discussion of the master oscillator circuit is limited to the circuit shown in figure 22, which results when transmitter tuning unit TU-6-A is
37
TM 11-273
29
SIGNAL CORPS
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39 ®
TM 11-273
29
SIGNAL CORPS
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40
TM 11-273
RADIO SETS SCR-193-A, ETC. 29
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Figure 18.—Radio set SCR-193-B, schematic diagram—Continued.
41
TM 11-273
29
SIGNAL CORPS
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Figuke 22.—Radio transmitters BC-191-A and BC-191-C, functional diagram of radio frequency and high-voltage circuits.
oscillator tube from the rectified grid current. Capacitor 1108 is a radio-frequency bypass capacitor. Grid choke 611, in conjunction with resistor 1109, serves as the necessary d. c. path from the grid to the filament, maintaining at the same time a high impedance to the radio-frequency grid excitation. Capacitor 1104 is the calibration reset by which the master-oscillator frequency can be adjusted to
45
TM 11-273
29 SIGNAL CORPS
correspond to the calibration whenever the oscillator tube is changed. This capacitor is adjusted through a small port in the front panel to the right of the TEST KEY. Capacitor 1103 is a sealed capacitor which provides the necessary thermal compensation for any frequency drift normally caused by warming up and variation of the ambient temperature of the oscillator tube.
c. Power amplifier circuit.—The power amplifier circuit is schematically illustrated in conjunction with the master oscillator circuit in figure 22. The power amplifier plate tank circuit, by means of which the plate load impedance is adjusted, is contained in transmitter tuning unit TU-5-A or TU-6-A, as the case may be. When the transmitter tuning unit TU-6-A is employed, and the BAND CHANGE SWITCH, A, is in position 2 (fig. 21), the plate tank circuit comprises the tapped coil 621 and variable capacitor 627. Moving the BAND CHANGE SWITCH to position 1 places the fixed capacitor 623 in parallel with the variable capacitor 627 and enables this tuning unit to cover the lower frequency range of the tuning unit. Continuous frequency adjustment of the plate tank circuit is accomplished by means of the variable capacitor 627, control C. Controls, coil, and capacitors of transmitter tuning unit TU-5-A (fig. 20) are arranged for similar operation on four bands, all of which are lower in frequency than those obtained with transmitter tuning unit TU-6-A. Subsequent discussion of the power amplifier circuit is limited to the circuit shown in figure 22, which results when the transmitter tuning unit TU-6-A is used and is set with the BAND CHANGE SWITCH on position 2. The poweramplifier grid receives excitation through capacitor 609 from the master-oscillator tank coil. Capacitor 609 also isolates the masteroscillator d.c. plate voltage from the power-amplifier grid. The power-amplifier grid bias is obtained from the flow of rectified grid current through resistors 614, 1112, 1113, and 1114. Choke 608 provides a low-impedance path for the d.c. grid current but a high-impedance path at radio frequency. Plate voltage for the power amplifier is applied through the modulation transformer 1164, the r.f. choke coil 1118, and the tank coil 621. The capacitor 1117, in conjunction with choke coil 1118, prevents r.f. currents from flowing into the power supply. The neutralizing capacitor 612 forms a part of a bridge circuit, including the power-amplifier grid-plate capacitance. Balancing this circuit by means of capacitor 612 prevents any interaction of the power amplifier on its grid-input circuit, thus eliminating the possibility of self-oscillation of the amplifier. All transmitter tuning units are properly neutralized at the time of manufacture and should never require adjustment in service unless
46
TM 11-273
29
RADIO SETS SCR—193—A, ETC.
the setting is accidentally disturbed. The power amplifier is inductively coupled to the antenna circuit by means of a tapped inductor 628, the taps of which are selected by a panel-controlled, tapped
PA.
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Figure 23.—Radio transmitters BC-191-A and BO-191-C, functional diagram of audio frequency circuits, tone operation.
switch D. Sufficient variation in coupling is provided to allow operation into a wide range of antenna resistances.
d. Modulation (fig. 23).—Modulating voltage is applied to the plate circuit of the power amplifier by means of the modulation transformer
47
TM 11-273
29
SIGNAL CORPS
1164. The modulator tubes 1161 and 1162 are operated in a push-pull, class B circuit in which they are biased nearly to cut-off. The modulator tubes receive excitation from the speech amplifier tube
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Figure 24.—Radio transmitters BC-191-A and BC-191-0, functional diagram of audio frequency circuits c. w. operation, side tone.
1154, through an interstage transformer 1157. The secondary of this transformer is loaded by resistors 1181 to reduce the effective load variation caused by the modulator grid current. Plate power
48
TM 11-273
29
RADIO SETS SCR—193—A, ETC.
for the speech amplifier is obtained from the positive high voltage through resistor 1156 which limits it to the proper value. Capacitor 1155 serves as an audio frequency bypass for this power source. Receiver side tone for monitoring the transmitted signal is provided by a tapped winding on the interstage transformer 1157. Switch 1179 selects the proper tap on this transformer winding to give the proper side tone level.
e. Tone, c. w., and voice operation.—(1) The TONE CW VOICE switch, 1141 (fig. 25), serves to select the desired type of transmission. It performs the following functions:
(a) It controls the modulator filaments.
(6) It controls a line compensating section of the filament resistor 1138 (fig. 26).
(c) It controls the tone-oscillator feed-back circuit.
(d) It connects the microphone circuit to the input transformer 1149 for VOICE operation.
(2) With switch 1141 in the TONE position (fig. 23), capacitor 1142 feeds energy from the speech amplifier plate to its grid in the proper phase relation to cause oscillation at an audio rate, and thus the required tone voltage is generated. The secondaries of input transformer 1149 and interstage transformer 1157 are resonated by capacitors 1150 and 1180, respectively, to provide the required tuned circuits in both grid and plate circuits of the a. f. oscillator (speechamplifier on voice). The tuning of these circuits is such as to establish a frequency of oscillation of about 1,000 c. p. s. Resistor 1151 on the primary of input transformer 1149 serves to stabilize the grid excitation of the speech-amplifier tube. The modulator tubes receive their excitation from transformer 1157.
(3) For c. w. operation (fig. 24), switch 1141 shuts off the modulator tubes by removing the filament power. The speech amplifier functions the same as for tone operation, although it furnishes only the audio frequency signal for monitoring the c. w. transmission.
(4) For voice operation (fig. 25), switch 1141 disconnects the tone capacitors 1142, 1150, and 1180, connects the microphone circuit to the primary of the input transformer 1149, and makes the modulator tubes operative by connecting their filaments to the supply. Potentiometer 1148 is the input level control. The speech amplifier will then receive its excitation from the microphone by means of input transformer 1149. The transmission is monitored through the receiver side tone circuit.
/. Bias voltages.—Bias for the modulator tubes is obtained from resistor 1113, and bias for the speech amplifier from resistor 1114 (fig. 23). These resistors form a part of the power-amplifier grid
296642 ----4
49
TM 11-273
29
SIGNAL CORPS
leak, the voltage across them resulting from the rectified grid current of the power amplifier. Capacitors 1144 and 1160 serve to bypass the speech amplifier and modulator bias, respectively, at audio fre-
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Figure 25,-Radio transmitters BC-191-A and BC-191-C, functional diagram of audio frequency circuits, voice operation.
quency. Both the modulator bias control (labeled MOD BIAS), and the speech amplifier control (labeled S. A. BIAS), are accessible in the tube compartment. The speech-amplifier grid bias is usually
50
TM 11-273
RADIO SETS SCR-19 3-A, ETC. 29
MOD
M.0 PA H61 SA
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Figure 26.—Radio transmitters BC-191-A and BC-191-C, functional diagram of low-voltage and control circuits, d. c. operation.
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Figure 27.—Radio transmitters BC-191-A and BC-191-C, functional diagram of antenna tuning equipment.
51
TM 11-273
29 SIGNAL CORPS
adjusted at the time of manufacture, and its value is not particularly critical.
g. Keying—Keying of the transmitter (fig. 22) is controlled by means of resistor 1115, one end of which is connected to the negative high voltage and all grid circuit returns, and the other end to filament or ground potential. The keying contacts of relay 1165 are connected across this resistor. When the keying contacts are open, the grids of the tubes are biased beyond cut off, and oscillation is stopped. When these keying contacts are closed, resistor 1115 is shorted and normal grid biases on all tubes are reestablished. Operation of the keying contacts is accomplished by supplying power to the antenna switching relay 1165. (See fig. 26.) Power is supplied to this relay when the key, test key, or the microphone keying button or switch is operated. Operation of the antenna switching relay performs the following additional functions:
(1) Disconnects the receiver from the antenna and grounds the receiver input circuit.
(2) Connects the transmitter to the antenna circuit.
(3) Keys the side tone circuit.
h. Filament circuit.—The transmitter is so designed that it may be operated from an a. c. source in connection with a power-supply unit consisting of a high-voltage rectifier for plate supply, a low-voltage rectifier for the control units, and a transformer to furnish a. c. filament supply. The AC DC switch 1136-1137 (figs. 3, 17, and 26) performs the circuit changes to allow the transmitter to be operated from either source. In the a. c. position the filament circuit is separated from the control circuit, and the normally grounded side of the filament is disconnected from ground. Capacitors 1107 (fig. 26) then serve to maintain the tube filaments at ground potential with respect to radio frequency currents. Under the condition of d. c. filament supply, resistor 1138 is used to adjust the filament potential to 10 volts, as indicated by the red line on voltmeter 1133. The midtap of this resistor is connected to the power source. One side of the resistor is used for the adjustment of the filaments of the tubes used for c. w. operation and the other side for the modulator tubes. Provision is made to short out a section of the c. w. filament resistor by means of switch 1141 ((b), fig. 26) to compensate for the increased line drop which occurs when the modulator filaments are lighted. This arrangement makes it necessary to readjust the voltages when changing from c. w. to tone or voice. A portion of the resistor may be short circuited by the 12V 14.2B switch 1139, 1140 (figs. 3 and 26), so that the correct filament voltage may be applied both when the power-supply storage battery is being charged and when
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not being charged. Switch 1135 connects filament voltmeter 1133 to either the c. w. or modulator filaments. If the filaments are operated from an a. c. source resistor 1138 serves simply as a compensating resistor to eliminate the need for readjusting the filament rheostat when changing from c. w. to modulated transmission.
i. Antenna tuning equipment.—(1) The antenna tuning equipment on the transmitter is capable of tuning practically any antenna to frequencies between 1,500 to 4,500 kc. Inductive and capacitive loading, and series and parallel tuning are provided. The selection of a suitable tuning circuit and its subsequent tuning are readily accomplished by observation of the antenna current meter and the total plate current meter. The latter meter by its sharp dip at resonance indicates most exactly the point of resonance. In the case of the vehicular installations described herein, the antenna is comprised of mast base MP-37, and antenna mast sections MP-49 to MP-53, inclusive. This antenna, when operated on a frequency between 1,500 and 4,500 kc., radiates most effectively with inductive series tuning.
(2 ) The types of loading and tuning desired are selected by means of the following controls located on the right front of the transmitter (see figs. 3 and 27):
(a) The meter marked ANT CURRENT is the radio frequency meter 1166, which indicates the r. f. currents in the various networks of the antenna tuning equipment.
(6) The dial marked ANT IND TUNING, M, is the control for the continuously variable loading inductor 1167, and is so calibrated that the inductance included is proportional to the dial reading.
(c) The switch marked ANT CIRCUIT SWITCH, N, is the control by means of which any one of the four antenna tuning networks is selected. The numbered positions on the switch correspond to the circuits as numbered in figure 27.
(d) The dial marked ANT CAP TUNING, O, is the control by means of which the capacitor 1169 is varied, and is so calibrated that the capacity included is proportional to the dial readings.
(e) The switch marked ANT IND SWITCH, P, is the control for the tapped inductor 1170, and is so constructed that the higher numbered positions correspond to the greatest amount of included fixed inductance.
(/) The switch marked ANT COUPLING SWITCH, D, 629 (fig. 21) located on the transmitter tuning unit is the control for the antenna coupling coil of the transmitter tuning unit and is used to control the coupling from the power amplifier circuits to the antenna tuning equipment and antenna. It is so constructed that the percentage of coupling is proportional to the number of the switch position.
53
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29 SIGNAL CORPS
(3) The antenna tuning networks (fig. 27) are selected and adjusted as follows:
Caution. Set the control D (2)(/) above) at 1 before beginning any antenna tuning operations.
(a) With the control N on position 1, the transmitter works in to a resonant circuit, in which the high voltage built up across the antenna tuning capacitor is used to “ voltage feed” the antenna. This circuit is generally used for high frequencies and fairly long antennas and is seldom used in tuning the standard vehicular antennas. The antenna feed circuit is maintained at resonance by means of control M, while the voltage fed to the antenna is varied by means of the control O, and resonance is indicated by the ANT CURRENT meter. The current in the feed circuit is adjusted by the control D and should not exceed 6 amperes. The step-by-step tuning procedure is as follows:
1. The control O is set at some arbitrary scale reading.
2. The circuit is resonated by means of the control M for a maximum reading on the antenna current meter.
3. The control D is adjusted so that the antenna current reads slightly below 6 amperes.
4- The circuit is reresonated as in 2 above.
5. The above procedure is repeated until the proper power amplifier loading is indicated on the total plate current meter (200 to 220 ma. on c. w.). Under the same conditions of power amplifier load, the lower the dial reading on the control M and the lower the reading on the antenna current meter, the more power will actually be delivered to the antenna.
(6) With control N on position 2, the transmitter works into a series resonant circuit. The antenna is “current fed.” The antenna circuit is resonated by means of controls M and O. Resonance is indicated by a maximum reading on the ANT CURRENT meter. The circuit is used generally for operation near the fundamental frequency of an antenna and therefore is not particularly efficient for tuning the standard vehicular antenna. When this tuning network is selected, the value of capacity should be the maximum for which an inductance value can be found that will give resonance. (This will be a minimum inductance value.)
(c) With control N in position 3, the transmitter works in to a series resonant circuit providing “current feed” and inductive loading. This circuit is used for operation below the fundamental frequency of the antenna and is generally used when tuning the standard antenna,
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RADIO SETS SCR—19 3—A, ETC.
operating on the higher frequency assignments for these installations.
1. The antenna circuit is resonated by means of the continuously variable inductor controlled by M.
2. Resonance is indicated by the dip in the total plate current and the indication of current on the antenna circuit meter.
3. Having found resonance, the transmitter is loaded by advancing control D until the proper plate current is indicated on the total plate current meter (200 to 220 ma. on c. w.).
(d) With the control N or position 4, the antenna circuit is identical with that obtained on position 3 except that an additional inductor controlled by P is added in series with the variable inductor 1167. This circuit is used when the operating frequency is relatively far below the fundamental frequency of the antenna, as will be the case when these installations and the standard antenna are operated on frequency assignment of 1,500 kc. and somewhat above. The adjustment of this circuit is accomplished as follows:
1. Control D is set on 1.
2. Control P is set on 1.
3. Inductor control M is rotated through its limits, while the total plate current meter is watched for any indication of a resonance (sharp dip). If resonance is found, the transmitter is loaded to its proper value.
J. Should resonance not be found at this setting of P, successively advance P to higher values, and repeat the variation of control M for each position of P until resonance is found.
(e) The change in antenna circuit constants, as a result of tuning, reflects into the tank circuit of the power amplifier. This necessitates a retiming of the power amplifier. The tuning of an antenna is not complete until the power amplifier and antenna circuits are both resonated to the transmitter frequency. Under some conditions (see par. 21e) it may be possible to resonate an antenna on either position 3 or 4 of control N. Operation on position 3 of control N is used when there is a choice.
j. Remote operation (fig. 18).—Radio control box BC-309 provides means for turning the transmitter off and on and for connecting the transmitter key. It merely parallels identical controls on the transmitter. Control box BC-321 may be used to turn the transmitter off and on and to connect the microphone. It also parallels identical controls on the transmitter proper. Remote operation of the transmitter may be accomplished at the location of these control boxes. Radio control box BC-309 contains, in addition to the OFF ON switch 1302, a key jack 1303, a pilot light 1304, and a socket 1301.
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TM 11-273
29-31
SIGNAL CORPS
Control box BC-321 contains, in addition to the OFF ON switch and the microphone jack, two headset jacks and two potentiometers, providing individual control for the two headsets. The connection of cord CD-297 from terminals 10 and 13 of the terminal box to the control box BC-321 supplies audio output from the receiver to the control box.
30. Dynamotor units BD-77-A and BD-77-B (fig. 9).—a. Dynamotor units BD-77-A and BD-77-B provide the high voltage plate supply for radio transmitters BC-191-A and BC-191-C, respectively. Each consists of a dynamotor on top of which is mounted the relay fuse box containing the starting relay, fuses, and filter elements. The unit is rated 14 volts—40 amperes input, 1,000 volts—0.35 ampere output, at 5,000 r. p. m. with 55° C. rise, for one-half hour intermittent duty. Dynamotors BD-77-A and BD-77-B are substantially identical in external appearances and mounting details, and BD-77-B is more conservatively rated at the values given above than is BD-77-A.
b. The dynamotor has a double armature winding consisting of a low-voltage (12-volt motor) winding and a high-voltage (1,000-volt generator) winding. Each winding terminates at a commutator on either end of the armature. The windings are carefully insulated from each othei. The field is common to both motor and generator windings and is excited from the 12-volt storage battery supply. Skeleton-type bearing brackets on each end afford maximum accessibility of the commutator and brushes. The external leads of the dynamotor go directly into the relay fuse box through two bushings in the top of the magnet frame.
c. Within the relay fuse box (fig. 10) is mounted a molded terminal board. On this terminal board are mounted the starting relay, low-voltage and high-voltage fuses, and the elements of the filter circuit. A totally inclosed solenoid type starting relay is used. A spare high-voltage fuse, spare fuse link, and a socket wrench are carried in clips inside the cover of the relay fuse box. In one end of the relay fuse box are mounted sockets SO-39 and SO-41. A x%6-inch diameter hole for entrance of a conduit containing the two power input leads is provided between these sockets.
31. Radio receivers BC-312 and BC-312-C.—Radio receivers BC-312 and BC-312-C are practically identical and are of the multiband, integral coil, superheterodyne type, and employ metal tubes throughout. Specific differences are pointed out as various elements of the circuits are discussed. Unless specifically referred to a particular type receiver, the discussion herein applies equally to each. Provision is made for the reception of c. w., tone, or voice signals over the frequency range of 1,500 to 18,000 kc., in six steps as follows:
/ ' 56
TM 11-273
31
RADIO SETS SCR—193—A, ETC.
Band
A.
B.
C.
I)
E.
F.
Frequency coverage excluding overlap, kc.
1,500 to 3,000
3,000 to 5,000
5,000 to 8,000
8,000 to 11,000
11,000 to 14,000
14,000 to 18,000
a. General circuit.—Figure 28 is a functional circuit diagram of radio receiver BC-312 showing the connections set up by the band change switch to receive a signal in one particular frequency band. In this functional diagram the band change switch itself, and all coils and capacitors not essential to the operation on that band, are omitted for the sake of simplicity. Radio receivers BC-312 and BC-312-C employ two stages of pentode radio frequency amplification, a pentagrid mixer and separate triode radio frequency oscillator, two stages of pentode intermediate frequency amplification, a duodiode-triode which performs the functions of a diode detector and one stage of audio frequency amplification, and a separate stage of pentode audio frequency amplification. The separate triode oscillator is provided to produce a beat note for c. w. reception. The antenna circuit of the receiver provides a means of transferring the desired signal to the first radio frequency stage, and also provides a means of transferring local noise to the first stage on bands A and B phased in such a manner that the total noise is materially reduced below that normally picked up on the antenna. The two radio frequency stages provide selectivity and also act to reduce possible interference from signals occurring at either the intermediate frequency or at the so-called repeat point, or image frequency. The mixer tube circuit with its associated oscillator adds to the selectivity of the receiver, and also changes the frequency of the signal from the frequency received to that at which the intermediate frequency amplifier is tuned. The intermediate frequency stages provide additional selectivity and gain. The second detector stage demodulates the amplified signal to audibility. The audio frequency stages provide additional amplification. The c. w. oscillator, operating at a frequency slightly different from that to which the intermediate frequency stages are tuned, provides an audible beat frequency adjustable in pitch when receiving c. w. signals.
57
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31 SIGNAL CORPS
c c /Zc /c '7 v%£___ I *#*-£” .% y?,g
vpJ kfH^n M rMppH Up4r“P M% -J 1 j. cj X ♦ f______________ Tc» C«'X / $*/ 5» ♦>: : : 1 ■ A>
I----------------------------------;__CATHpar bus_______ / ?/ f \ sw T
3t TL-fdQS
Figure 28. Radio receiver BC-312, functional diagram, manual volume control operation.
58
TH 11-273
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RADIO SETS SCR—193—-A, ETC.
b. Antenna circuit (figs. 28 and 31).—The antenna circuit is coupled to the tank coil of the first radio frequency stage (LJ through capacitor C26. L25, L26, and L27 are inductances added to the circuit to permit canceling out locally generated noise normally received on the signal antenna. In addition, coil L27 serves as a radio frequency choke between the antenna and ground. The functioning of this noise suppression circuit is described in detail in k below. Capacitor C28, controlled by the knob on the front panel marked ALIGN INPUT, in conjunction with changes in connections of L25, L26, and L27 produced by the band change switch, permits tuning the antenna circuit to resonance to an incoming signal. LMX is a neon lamp which, normally has a very high resistance. When a certain threshold voltage is exceeded, the lamp becomes a conductor by ionization and prevents further rise in voltage, bypassing the current to ground. It is used in this circuit to protect the receiver from any excessive voltages which might be applied to the antenna.
c. Radio frequency (fig. 28).—The circuits of the first radio frequency, second radio frequency, and mixer stages are very nearly identical. They are so designed to permit tuning with a single control gang capacitor. The screen voltages for the first radio frequency, second radio frequency, and mixer tubes are provided by voltage dividers connected between plus plate voltage and ground. R2 and R3; R8 and R9; and R48, Ris, and R50 form these voltage dividers. The screen grids are bypassed to ground across these voltage dividers by capacitors C30, C36, and C49, respectively. Cathode bias for the first radio frequency and second radio frequency tubes is partly fixed and partly variable. The fixed portion of this bias is secured by the drop across Rj ahd R7, respectively, and from the junction of these resistors to the variable bias at the voltage divider formed by R36 and adjustable resistor R35. R35 is shorted to ground for automatic volume control (a. v. c.) operation and in this mode of operation the cathode biases of these tubes are secured entirely by the drop across Ri and R7. The cathode bias of the mixer tube is secured by the drop across R14. The injector grid return is through resistor Ri3. C29, C35, and C48 are bypasses to ground across the cathode biasing resistors. C33 and C45 keep the plate voltages from the preceding tubes from reaching the grids of the second radio frequency and mixer tubes, respectively. C10i in the first radio frequency stage is used to make the grid circuit of this stage identical with those of the two succeeding stages to permit the gang tuning referred to above. Li, L7, and L13 are the tank inductances of the grid circuits of the first radio frequency, second radio frequency, and mixer stages, respectively. The plate circuits of the first radio frequency and second radio frequency
59
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SIGNAL CORPS
tubes are conductively coupled to the tank inductances of the next succeeding stages. These tank inductances are tuned by a gang capacitor consisting of C28, C34, and C46. In series with the sections of this gang capacitor are three capacitors, C2S, Cloo, and C38, across which is placed a gang control switch SW2, SW4, and SW6 (operating with the band change mechanism). This gang control switch permits these series capacitors to be used in the three higher frequency bands to obtain a greater frequency spread on the dial, and shorts these capacitors in the three lower frequency bands. Trimmer capacitors Cb C7, and C13, are provided to permit individual preadjustment (aline-ment) of the three circuits involved to resonance at a given input frequency with one setting of the gang tuning capacitor. C32 and C39 serve as radio frequency bypass capacitors and in conjunction with R5 and Rn, respectively, isolate the d. c. plate supply from radio frequency currents. As blocking condensers, they prevent the shorting of the plate supply of the first and second radio frequency tubes to ground. C27 in the first radio frequency stage is placed in the circuit to make the latter identical to those of the second radio frequency and mixer stages for purposes of gang tuning. C102, C99, and C62 act as bypass capacitors for a. v. c. operation. R4 and R53; Rs and R10; R12 and R16 provide a high impedance d. c. grid return for the tubes involved and also provide a path through which a. v. c. voltages are applied. The grid return of these three stages is made through resistor R29 to ground for m. v. c. operation and through R29 and R30 for a. v. c. operation. The purpose of R30 is explained in detail in j below. R5, Ru, and R17 are in series with the plate leads of the tubes involved, and with capacitors C34, C37, and C54, in conjunction with Cm, serve to reduce to a negligible value the amount of radio frequency reflected back into the power supply circuit from these tubes.
d. Radiofrequency oscillator (fig. 28) .—The radio frequency oscillator employs a modified Hartley circuit with the plate end of the tank circuit operating at ground potential for radio frequencies. The tank circuit of this oscillator consists of inductance Li9, which is tuned by C32. C82 is ganged with the main tuning capacitors C28, C34; and C46, C40, in series with C82, is used in the three higher frequency bands to obtain greater frequency spread, but is shorted out by switch SW8 in the three lower frequency bands. Switch SW8 is ganged with switches SW2, SW4, and SW6. Ci9 is a trimmer capacitor which adjusts the tracking of the oscillator stage with the other tunable stages of the receiver. C42, C43, and C44 (see figs. 17, 18, and 19), while not essential to the functioning of the oscillator circuit, are included in the tank circuit to make it suitable for tracking in all bands with those of the radio frequency and mixer stages. C88 serves as a grid-blocking capac
60
TM 11-273
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RADIO SETS SCR-193-A, ETC.
itor and R42 as a grid-bias resistor. R41 and R46 together serve to reduce the plate voltage supplied by the dynamotor to the proper value for this tube. R44, R45, and R46 are different for the different frequency bands of the receiver to insure that the plate voltage on the oscillator tube will be correct in each band. The radio frequency plate circuit of the oscillator is completed through C83 and ground to the tank circuit. The radio frequency voltage occurring between the cathode of the oscillator tube and ground is impressed on the injector grid of the mixer tube (1st detector) through C47. The action of the mixer and oscillator on the received signal produces an output signal of 470 kc., having the same modulation as the signal received in the antenna. The intermediate frequency amplifier is tuned to 470 kc.
e. Crystal filter (figs. 28 and 29).—The output of the mixer stage is inductively coupled to the grid circuit of the first intermediate frequency stage through transformer L28. C53, in parallel with the primary of this transformer, forms a resonant circuit which is tuned to 470 kc. by varying the position of an iron core within the transformer coil. The secondary of this transformer and both coils of transformers L29 and L30 are tuned in a similar manner. In the grid side of transformer L28, there is a bridge circuit consisting of capacitors C94, C95, and C5i and crystal CX. This crystal is provided with a shorting switch SW10. With this switch closed, the secondary of L28 and capacitors C94 and C95 form a resonant circuit tuned to the intermediate frequency so that one-half of the available voltage across the secondary of inductance L28 is impressed on the grid of the first intermediate frequency tube through blocking capacitor C52. When switch SWio is open (by turning the CRYSTAL PHASING control from the OUT position), the signal is impressed on the grid of the first intermediate frequency tube through crystal CX and through capacitor C52. Crystal CX is cut to the intermediate frequency of 470 kc. CX behaves as a sharply tuned resonant circuit and offers a high impedance to all frequencies, except its resonant frequency. The capacity of the crystal holder would normally serve as a bypass to this resonant circuit, reducihg its impedance. For this reason, the bridge circuit consisting of capacitors C94, C95, and C5i permits balancing out the effect of the capacity of the crystal holder and raises the impedance of the circuit to frequencies other than the resonant frequency. Any other adjustment of capacitor C5i provides a bypass around the crystal and reduces the circuit impedance to undesired signals. This control is referred to as the CRYSTAL PHASING control since the crystal, neglecting the effects of the holder, behaves as a resonant circuit with the current and voltage very nearly in phase. Introducing
61
TM 11—273
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SIGNAL CORPS
j 1 ST. I.F.
I ST. DET | ___________ | __
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Figure 29.—Radio receiver BO-312, functional diagram, crystal selectivity filter operation.
02
TM 11-273
31
RADIO SETS SCR—19 3—A, ETC.
a capacitance disturbs this condition of resonance and introduces a phase difference between the current and voltage, the magnitude of which is determined by the degree of unbalance.
/. Intermediate frequency amplifier (fig. 28).—Resistor R18 provides a high impedance direct current grid return for the first intermediate frequency tube, and in series with R52 provides for the introduction of a. v. c. voltage. C63 is a radio frequency bypass to ground shunting radio frequency out of the a. v. c. circuit. The coupling between first and second intermediate frequency stages, and between the second intermediate frequency stage and the second detector, is inductive through transformers L29 and L30. Both sides of both of these transformers form circuits which are resonant to the intermediate frequency, the necessary capacitance being provided by C57 and C9i j C77 and C55; C85 and C93; Cg4 and C92. C77, C9i, C92, and C93 are not used in BC-312-C. The necessary tuning to secure resonance is achieved through the use of movable iron cores in the same manner as in transformer L28. The resistor R19 has the same voltage divider system as for the first and second radio frequency tubes. The cathode bias for the second intermediate frequency tube is obtained through resistor R24. The grid return of the second intermediate frequency tube is through resistor R23, which provides means for introducing a. v. c. voltage, and with capacitor C56 prevents radio frequency from feeding into the a. v. c. circuit. The screen voltages of these two tubes are obtained from the voltage dividers consisting of R20 and R21, and R25 and R26. These screen grids are bypassed to ground by capacitors C60 and C69, respectively. C59 and C68 serve to bypass the cathodes to ground.
g. Second detector (figs. 28 and 30).—A duo-diode-triode is employed as a second detector, one diode circuit actually serving for purposes of demodulation, the other diode circuit providing for a. v. c. action. The triode portion of the tube serves as the first audio frequency amplifier. These two latter functions will be described in detail in subparagraphs below. The cathode and the detector diode plate (fig. 28) act as a half-wave rectifier so that any current flowing through resistors R49 and R34 is pulsating. Any portion of the drop across these resistors may be amplified as audio frequency. C7i and C72 are placed in the circuit as radio frequency bypasses across these resistors. ■ R28 provides the proper cathode bias for this tube and is bypassed to ground by C73.
h. Audio frequency amplifier (figs. 28 and 30).—The triode portion of the detector tube serves as the amplifying tube for the first stage of audio frequency. This tube receives its grid excitation through capacitor C8i. This excitation consists of the drop across the entire
63
TM 11-273
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SIGNAL CORPS
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® Manual volume control.
64
TM 11-273
31
RADIO SETS SCR—193—A, ETC.
10 MME 2ND. DET.
1ST. R.F. 2ND. R.F I ST. DET. 1ST. I.F 2ND. I.F. c67.i__________ __________
--k ZX --1 —1 /\ i i r--—--------1 -1.T0 2ND. 51------51 >1 5 1----zx 5 S 5 5 L3Cgj p|5oMMR- I 1
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B+ - - - -TL-1900
® Automatic volume control.
Figure 30.—Radio receiver BC-312, functional diagram.
296642’^11----5
65
TM 11-273
31
SIGNAL CORPS
resistor R34 for m. v. c. operation and the drop across the lower portion of resistor R34 for a. v. c. operation. R32 serves as a high impedance d. c. grid return for the tube. The output circuit of the first audio frequency tube is coupled to the control grid of the second audio frequency tube through capacitor C76. The primary of transformer Tx acts as an impedance coupling element and also as the primary of the transformer for coupling to a secondary circuit containing Jb into which phones may be plugged. C74 in this circuit prevents audio frequency feedback into the power supply and completes the audio frequency plate circuit for this tube. R33 serves as a high impedance d. c. grid return for the second audio frequency tube. The cathode bias of the second audio frequency tube is provided by R3b which is bypassed to ground by capacitor C98. The output of the second audio frequency tube is coupled through transformer T2 to jack J2, into which phones may be plugged, and to J3 (see figs. 17, 18, and 19), into which a loud speaker may be plugged. In the case of the receiver BC-312-C, a 12 volt field supply is available in the connections of the jack J3 for those speakers requiring the same, providing the speaker is properly corded to the transmitter. Cording data is supplied with the speaker. C80 in this plate circuit prevents audio frequency feedback into the power supply and completes the audio frequency plate circuit.
i. C. w. oscillator (fig. 28).—A modified Hartley circuit is employed operating with the plate end of the tank circuit at ground potential for radio frequency. The tank circuit of this oscillator consists of coil L31 tuned by capacitors C84 and C85 in parallel. C86 is a grid-blocking capacitor and R43 is a grid-return resistor. The plate supply of this oscillator is obtained through switch SWU (CW OSC ON OFF switch) which permits turning this oscillator on or off at will. R37, in series with the d. c. plate circuit, serves to drop the plate voltage from that supplied by the dynamotor to the correct value for this tube. The radio frequency plate circuit is completed through capacitor C87 and ground to the tank circuit. A portion of the drop across tank coil L31 is impressed on the plate end of the second detector tank circuit through a low-pass filter consisting of C96, C97, R5b and L32 and through coupling capacitor C4b The purpose of this filter is to prevent the introduction of harmonics of the c. w. oscillator frequency into the detector circuit of the receiver.
j. Volume control.—(1) Manual volume control action (figs. 28 and 30®).—When operating on manual volume control (MVC), the cathodes of the first and second radio frequency tubes and the first intermediate frequency tube are returned to the voltage divider consisting of R35 and R36. This voltage divider is located between plus plate voltage and ground, so that changing the value of the resistor R35
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TM 11—273
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RADIO SETS SCR—19 3—A, ETC.
by operating the VOL control on the front panel changes this cathode bias and thus varies the gain of these tubes. R30 is shorted, preventing a. v. c. action described in (2) below. In this mode of operation, that portion of the audio frequency signal which appears across all of resistor R34 is available at the input of the first audio frequency tube.
(2) Automatic volume control action (figs. 28 and 30®).—For automatic volume control (a. v. c.) operation, resistor R35 is short circuited to ground. The audio frequency voltage available at the grid of the first audio frequency tube is now the voltage across that portion of R34 between ground and the sliding contact of resistor R34. Changing the position of this contact by operation of the VOL control on the front panel changes the amount of audio frequency voltage impressed on the first audio frequency tube without interfering with a. v. c. operation. The second diode plate of the second detector tube is coupled to the plate tank circuit of the second intermediate frequency stage through capacitor C67 to generate the a. v. c. supply voltage. A rectifier circuit exists between this plate resistor R30 to ground, thence through resistor R28 to the cathode. The cathode is maintained at a positive potential with respect to the a. v. c. plate by d. c. plate current in the triode section of the tube flowing through R28. Rectification will take place in this a. v. c. circuit when the peak value of the a. c. voltage impressed is greater than the d. c. drop across resistor R28, and this rectified voltage will appear across resistor R30. The magnitude of the voltage across R30 is therefore dependent upon the strength of the signal received in excess of the drop across resistor R28. Thus no a. v. c. action is obtained on signals whose a. c. peak value is less than the drop across resistor R28. This type of action is referred to as “delayed” a. v. c. In a. v. c. operation, the control grids of the first radio frequency, second radio frequency mixer, first intermediate frequency, and second intermediate frequency are returned to ground through resistor R30. A change in the voltage across resistor R30 therefore affects the bias and gain of these tubes. The circuit is designed to bias these tubes more negatively on a strong signal, thus reducing their gain and tending to maintain a constant input to the detector.
k. Noise suppression circuit (figs. 28 and 31).—(1) A circuit is provided for the purpose of reducing interference on bands A and B caused by poorly shielded engine ignition systems. Three inductance coils L25, L26, and L27 function when properly adjusted to reduce this type of interference. L25 is coupled to L26, an electrostatic shield being provided to insure that this coupling is entirely magnetic. This coupling is also adjustable. The coupling between L26 and L27 is primarily electrostatic, the necessary magnetic shield being provided to insure
67
68
TM 11-273
31 SIGNAL CORPS
NOISE ANT. SIGNAL ANT. BANDA CIRCUIT REFERENCES SHOWN
TW BAND B FUNCTIONS IDENTICAL
L25 , I
NOISE®) 1 9JSIGNAL • COIL®) | QxCOIL ------7TjOl26________..X __________ ..C|Q|
[ x SW2l iC25 F3 C
COUPLING O X , >
C0ILL?73 ©LM| E ’ 7 C| 7^28 $R53 '
27A e-------------------—’H
C27 C|02
■=" ■=■ =• AVC
NOISE ANT. SIGNAL ANT. BAND C CIRCUIT REFERENCES SHOWN
Y Y
L25 . ±25
-----_9 । 7) .|7 |.cioi
L27| 4)l«. p T3 fcgs „ ।
c27 y 102
~ ~ — AVC
NOISE ANT SIGNAL ANT. BAND D CIRCUIT REFERENCES SHOWN
V BANDSE8F FUNCTIONS IDENTICAL
. L26
L—F
□■U c,o,
CpLM, jo_________________________^C28 ||___? 53 '
4- 4- ~ AVC
TL-1901
Fig. 31.—Radio receiver BC-312. functional diagram of antenna circuits.
that this type of coupling is secured. The coupling between L26 and L27 is also adjustable. A knob on the front panel marked NOISE BALANCE controls the coupling between L26 and L25 and serves to adjust the amount of noise introduced into the receiver circuits from the noise antenna. The coupling between L27 and L2r, and controlled
TM 11-273
RADIO SETS SCR—193—A, ETC. 31
by the NOISE ADJUST control, determines the phase relation of the resultant noise voltage introduced into the receiver. The coupling between L25 and L26 is adjusted to produce minimum noise (not necessarily zero). L27 is then varied to reduce the noise to zero, thereby insuring that the phase of the noise fed by the separate antennas results in cancelation.
(2) In radio receiver BC-312-C, screws and locknuts are used to adjust the controls marked NOISE ADJUST and NOISE BALANCE.
I. Tube heater circuits.—Metal tubes of the heater type are employed in radio receiver BC-312. These tubes require a heater voltage of approximately 6 volts per tube. To permit operation on a 12-volt
TO TUBE HEATERS . I Fl
___I I__________________________ LV<
I
LM2 lm3
pw'2
| — — — sWj^ — ———— i N0T A PARr Of.
| __o A----------- ] BC-312-C
*38
I --WAA--------------------
R39
।---VWvN-------------------
R 40 r
I .., 1” |THS) |
l-T.frt2—T-—i!
~ TL-1Q02A
Fig. 32.—Radio receivers BC-312 and BC-312-C, functional diagram of low-voltage circuits.
power supply system, these tubes are connected in a series-parallel combination, with two tubes which require the same heater current connected in series, and then these pairs arranged in parallel. Tube heaters are bypassed by C78 and C79. Actual heater connections are shown in figures 17, 18, and 19.
m. Oscillator compartment heater circuit {BC-312 only) (fig. 32).— In order to maintain the radio frequency oscillator at a constant frequency for a given setting of its tuning capacitor, the entire circuit is installed in a heat-insulated compartment. The use of electric heaters and thermostats maintains this compartment at a constant temperature of 110° F. R38, R39, and R40 are the heater elements for
69
TM 11-273
31 * SIGNAL CORPS
this chamber, the first two being connected in parallel and controlled by the temperature control THSj. R40 is cut out and into the circuit by temperature control THS2. In series with this combination is the switch SW13 (HEATERS OFF ON switch) which permits the heater circuits to be manually controlled. C89 and C90 are connected across the contacts of temperature controls THSi and THS2, respectively, to reduce interference caused by the opening and closing of the contacts. The two temperature controls are adjusted to open at 109° F. and 111° F., respectively. These values have been selected so that the temperature of 110° F. is maintained with the minimum number of temperature control contact breaks. Of the total heater capacity (49 watts with 14 volts input), 33 watts are used between 109° F. and 111° F., and 49 watts at 109° F. and below. When the temperature rises above 109° F., only 33 watts are applied to the compartment. At and above 1110 F., no heat is supplied. On the reverse cycle, as the temperature falls below 111° F., 33 watts are applied, slowing down the rate of temperature fall until 109° F. is reached, at which time 49 watts are applied. A fuse marked HEATERS, accessible on the front panel, protects the heater circuit.
n. Dial lamp circuit (figs. 19 and 32.)—Two dial lamps LM-27 (circuit symbols LM2 and LM3) are connected in series across the heater circuit in such a manner as to receive current through the heater fuse and be turned off and on by the OFF MVC AVC switch (BC-312). In radio receiver BC—312-C the dial lamps are connected in series and controlled by the OFF MVC AVC switch. The fuse marked LAMPS (circuit symbol F2) on the front panel protects this circuit.
o. The SEND REC switch.—The SEND REC switch controls the operation of a relay that shorts the input network of the receivers BC-312 and BC-312-C to ground at such times as the SEND REC switch is turned to SEND and the transmitter is keyed. At such times as no transmissions are intended, the SEND REC switch will be turned to the REC position. The purpose of the relay shorting function is to keep at a minimum the voltages built up in the receiver circuits when the high energy signals from the transmitter are radiated in close proximity to a receiver of the sensitivity of the BC-312 type.
p. Dynamotor DM-17-A and DM-21-B (figs. 33, 34, and 35).— Dynamotor DM-17-A, operating on an input voltage of 12 to 14 volts, produces the necessary plate voltage for the receiver BC-312. This dynamotor is secured to the underside of the chassis of the receiver. Under full load conditions, the dynamotor requires 2.7 amperes at 14 volts d. c., with an output of approximately 82 milliamperes at 230 volts d. c. (See fig. 33.) Li and Q constitute a filter
70
TM 11-273
31
RADIO SETS SCR-19 3-A, ETC.
circuit to prevent radiation of radio frequency interference into the low-voltage supply circuit. L2, L3, and L4, together with capacitors
CAPACITORS C|______0.3 MF.
C2_______20 MF.
C3______0.3 MF.
C4______005 MF.
COILS
«-n
l3 J>r.f. chokes
L2______CHOKE
TL-igOJA
Figure 33.—Dynamotor unit DM-17-A, functional diagram.
_ PLnamoto^ dm -
। । । _e ।
i --------------------------------® a+I
1 i i
i 1 l—I ^EEN..w B-i
। - |. r x ।
I DYNAMOTOR ' । FILTER FL-6-B
!_________________!_i_________________I
TL- 2243
Figure 34.—Dynamotor unit DM-21-B, with filter unit FL-6-B, schematic diagram.
C2, C3, and C4, constitute a combination audio frequency and radio frequency filter circuit which reduces commutation ripple to a value
71
which will not be objectionable and also prevents radio frequency interference from being transmitted by the dynamotor to the receiver circuits. Dynamotor DM-21-B is similar to and performs the same functions for the radio receiver BC-312-C (fig. 34). Under full load conditions, this dynamotor requires 3 amperes at 14 volts d. c., with an output of approximately 90 milliamperes at 235 volts d. c. A filter unit FL-6-B prevents radiation of radio frequency interference into the low-voltage supply circuit, and also acts as a combination audio frequency and radio frequency filter circuit which reduces commutator ripple to a value which will not be objectionable, and also prevents radio frequency interference being transmitted by the dynamotor to the receiver circuits. The filter unit FL-6-B is readily removable in the case of DM-21-B. Dynamotor DM-21-B cannot be used to replace DM-17-A. (Circuit references in this paragraph are not listed in paragraph 41.)
Section IV
SERVICING AND REPAIR
Paragraph
Servicing__________________________________________________________________ 32
Inspections________________________________________________________________ 33
Lubrication________________________________________________________________ 34
Special adjustments to radio transmitters BC-191-A and BC-191-C____________ 35
Normal current, resistance, and voltage readings___________________________ 36
Procedure in case of set failure___________________________________________ 37
Locating trouble___________________________________________________________ 3g
Repairs. _____________________________________________________________ 39
72
TM 11-273
31 SIGNAL CORPS
F--- I. II I ]K<-'2
1-1 II I I || J---1 r--^SHIELDED CONTAINER
TERMINAL BOARD
/ GEN-E-MOTOR \ ’ /A + r
___________~_________i—_ FtI111
\l
W 22S2Z3Z (-12 V.XbLACk)
'4 B+ (RED)
JI (g (BLACK&WHITE)
F j C/i
\ ______________r/ Apgn M DYNAMOTOR CONNECTIONS
\ t—-n-rr ni 11T11111111111 OF A T0 SET AT 0OTTOM edge eA^(.'LT‘L
G- I2v. > T L - 22 AA
Figure 35—Dynamotor unit DM-17-A, interior view.
TM 11-273
32-33
RADIO SETS SCR-193-A, ETC.
32. Servicing.
Caution.—Care must be observed in servicing this radio equipment. Using personnel will make only such repairs as are indicated in paragraph 39. Servicing should be attempted only by competent personnel supplied with adequate test and repair equipment. An inexperienced operator, in attempting to locate and repair a minor trouble which a competent man could service in a few moments, may damage the equipment to such an extent as to require shipment to a depot for repair.
33. Inspections.—a. Daily inspection.—The various components of radio sets SCR-193-A, SCR-193-B, SCR-193-C, SCR-193-D, and SCR-193-E will be given a thorough visual inspection before and after each day’s operation to insure that the set is ready for use at any time. This inspection includes examination of all cordage for proper fastening and for damage. All accessible components are examined for dirt and cleaned if necessary. At the end of a long period of storage, this inspection also includes a check to see that the dynamotor armatures revolve freely.
b. 50-hour inspection.—A thorough inspection of the complete installation will be made after every 50 hours of operation. This materially aids in securing uninterrupted performance in the field. The procedure for this inspection is as follows:
(1) Check to see that the storage battery is at the proper specific gravity and that the charging generator and regulator are adjusted so as to keep the battery fully charged.
(2) Clean the accumulated dust and dirt from all units, using an air hose or bellows, paying particular attention to the loading coil, item 1170, in the antenna compartment of the radio transmitter. Inspect the rotating coil, item 1167, in this compartment, and clean the winding thoroughly with carbon tetrachloride and a clean cloth. The rod (only) on which the wheel runs should be touched in several places with oil dag to insure smooth operation.
Caution.—Do not leave a surplus of oil dag such that the wheel and track surfaces will become contaminated by the lubricant.
(3) Make certain that all wiring is in place, that all mounting brackets and supports are rigidly fastened, and that all nuts and machine screws are supplied with lock washers and are tight.
(4) Determine that the cords are not damaged and that all ground connections are secure.
(5) Inspect plugs for proper fit and sockets for compressed pin springs. Pin springs which have taken a permanent set can usually be restored by a very fight hammer blow at the end of the pin.
73
TM 11-273
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SIGNAL CORPS
(6) Make certain that all cartridge fuses are held tightly in their clips. A loosely held fuse should be removed and the clips bent by hand until they grip the fuse tightly. Clean clips and fuse ends. Clean all contact surfaces.
(7) Inspect the high voltage fuses by removal from the mounting. Carefully clean all contact surfaces and replace the fuses.
(8) Inspect the antenna system for broken or frayed leads or loose mast sections. Wipe the insulator clean. To prevent loosening and loss of mast sections, joints should be covered with rubber tape. Make sure that antenna leads have not been bent close to metalwork where high antenna voltages might cause sparkovers.
(9) Inspect keys and microphones for defective cords and damaged plugs.
(10) Inspect dynamotor brushes for length. To inspect the receiving dynamotor DM-17-A and DM-21-B, it is necessary to remove the receiver chassis from its cabinet. Carefully place the chassis upside down and face the panel. Remove the cover of the dynamotor compartment DM-17-A by loosening the two knurled thumbscrews provided on the left-hand side and the two flathead screws on the right-hand side of the dynamotor. The brush holders on both the high and low voltage commutators will now be plainly visible, and either set of brushes may be removed without employing tools. Their removal is accomplished by stretching the helical springs and slowly but carefully disengaging the curved sections of the two brush holders from the posts in which they are engaged. Be careful not to break the soldered pig-tail connections. If it is desired to withdraw the brushes completely from the dynamotor, it will be necessary to unsolder the pig-tail connections on the brush holders. Inspect the face of each brush. It should show that at least 70 percent of the face of the brush is making contact with the commutator. The brush face should show no deep scratches or rough spots.
(11) Inspect both dynamotor commutators for cleanliness and for excessive wear.
(12) Rotate the dynamotor armature by hand, and make certain that it turns freely and is not rubbing against the field poles or leads. When the brushes have been removed, the armature should spin freely on its bearings.
(13) Upon completion of an inspection, all plugs and sockets should be completely reengaged and screwed down tightly. All tubes should be inserted all the way into their corresponding sockets and grid-cap connections, if any, firmly made. Chassis should be effectively locked in their boxes by means of the locking catches on the front panels.
c. Receiver vacuum tubes.—The vacuum tubes used in radio receiver
74
TM 11-273
RADIO SETS SCR—193—A, ETC. 33-34
BC-312 and BC-312-C normally have an effective life of 2 to 3 years. However, to insure best performance of the receiver, they should be checked with an accurate tube checker. Tubes should be checked particularly just prior to extended field maneuvers and those which do not come up to maximum standards should be replaced. If no tube checker is available, all tubes should be replaced annually, the receiver carefully checked for performance, and circuits realined if necessary.
34. Lubrication.—Lubrication should be accomplished in accordance with the chart below. Do not use excessive amounts of oil or grease and do not allow electrical connections to become greasy. Excess lubricant in dynamotors will tend to work out of bearing housings and onto commutators, where it will cause trouble; it also may cause the bearings to overheat. Make sure that lubricants and oilholes are clean and free from sand, grit, or dirt. These abrasives are the chief cause of bearing wear and the necessity for bearing replacement.
75
TM 11-273
34
SIGNAL CORPS
Lubrication chart
Ar>nar«fH« Points of lubri- Lubricant to be Quantity of a • • ,3 o ,
Apparatus catiOn employed lubricant Service periods Special instructions
Dynamotors Oil cups------ SAE 10 mineral oil- One drop each 500 hours__ These bearings are of the sealed,
DM-17-Aand bearing. ball bearing type, packed with
DM-21-B. grease at the time of manu-
facture. Any oil above the stated amount will do more harm than good.
Ball bearings. _ High temperature ball As required by Whenever arma- For removal of the armature of bearing grease 295 special in- ture is re- dynamotor DM-17-A, the grade Air Corps spec- structions. moved and re- dynamotor case must first be ification No. 36-50; placed. separated from the chassis.
“Refined Calol Turn the receiver chassis up-
Grease” made by side down and remove four
New Departure Mfg. screws holding the cover in
Co.; Grease made by place. After lifting this cover
N. Y. & N. J. Lubri- disconnect all leads to the recant Co. ceiver. Next, completely re-
move dynamotor DM-17-A. (Six screws in the front panel and two in the subpanel hold mounting brackets.) DM-21-B is removed by unsoldering all connections at the connection strip. Remove the two screws adjacent to the 1st i. f. and 2d i. f. tube sockets and
7(5
RADIO SETS SCR—19 3—A, ETC.
TM 11-273
34
77
the six screws holding the brackets to the front panel. It is then necessary to separate physically the dynamotor proper from its case. This is accomplished by removal of the soldered ground lead, the leads marked 1 and 2, and the unmarked lead, and lifting the unit from its cradle. This operation involves the forcing of the two U-brackets holding the four rubber mounting grommets. The end brackets are next removed and the armature withdrawn from position. The quantity of grease should be sufficient to cover thoroughly the ball bearing assembly surfaces. Excess grease should be removed.
TM 11-273
34
SIGNAL CORPS
Lubrication chart—Continued
Annnrafiix Points of lubri- Lubricant to be Quantity of o . . , „ . , . ,
pparatus cation employed lubricant Service periods Special instructions
Dynamotor units End bearing SAE 40 mineral oil- 3 to 5 drops- 2,000 hours op- Remove screw cap on the top of
BD—77—A and oilers. eration or at 6 bearing housing.
BD-77-B. month inter-
vals.
Ball bearings High temperature ball As required by 5,000 hours op- Remove the screw cap on the top bearing grease 295 special in- eration or at of the bearing housing and add
grade Air Corps spec- structions. yearly inter- approximately a % inch cube of
ification No. 36—50; vals. grease. At least every 2 years
‘■Refined Calol remove the armature from the
Grease” made by dynamotor, thoroughly clean
New Departure Mfg. the bearings and bearing hous-
Co; Grease made by ings with carbon tetrachloride,
N. Y. & N. J. Lubri- and repack each ball bearing
cant Co. with approved ball bearing-
grease. The quantity of grease should be sufficient to cover thoroughly the ball bearin assembly surfaces. Excess grease should be removed.
Radio receivers Gears and Petrolatum----------- Sufficient to per- When required _ _ The various gears and bearings
BC-312 and bearings of mi t quiet of the radio set chassis are
BC~312-C. band change smooth drive lubricated at the time of manu-
mechanism of mechanism facture with a sufficient amount
andconden- involved. of lubricant to last the life of
ser drive. the equipment, and unless op-
' erated in an abnormal manner
78
RADIO SETS SCR—19 3—A, ETC.
TM 11-273
34
79
should never require lubrication. In the event that such lubrication becomes necessary, petrolatum should be very sparingly used.
Radio transmit- Switch shafts. SAE 20 mineral oil_ Very thin film . Whenever ap-
ters BC-191-A paratus is re-
and BC-191- moved from
C; Transmit- service and
ter tuning thoroughly
units TU-5-A cleaned.
and TU-6-A;
Control box
BC-321 and
Radio control
box BC-309.
Switch con- White petroleum jelly. _ Very thin film_ Whenever ap-
tacts ; paratus is to
switching be removed
relay. from service
and thoroughly cleaned.
TM 11-273
35
SIGNAL CORPS
35. Special adjustments to radio transmitters BC-191-A and BC-191-C.—a. Auxiliary equipment.—The following auxiliary apparatus should be used to adjust properly radio transmitter BC-191-A. This auxiliary apparatus is not issued as a component of these sets but must be obtained elsewhere.
(1) One frequency meter set SCR-211-A.
(2) One radio frequency ammeter (0-1 ampere full scale).
(3) One 100-micromicrofarad condenser, either fixed or variable, capable of withstanding at least 2,500 or 5,000 volts d. c.
(4) One noninductive resistor of approximately 10 ohms, capable of carrying one ampere.
Note.—The condenser, resistor, and r. f. ammeter are connected in series, and the combination connected between the antenna and ground binding posts of the transmitter to form a dummy antenna load for the transmitter.
b. Neutralization.—Radio transmitters BC-191-A and BC-191-C are adjusted for neutralization by the manufacturer and normally will never require adjustment in the field. When necessary, neutralization may be checked and adjusted as follows:
(1) Turn the transmitter OFF ON switch to the OFF position.
(2) Remove the tube compartment shield.
(3) Remove the power amplifier tube (VT-4-C) from its socket and cover one and only one filament pin with a piece of paper and replace the tube. (When the transmitter is turned on, the power amplifier filament should not light.)
(4) Connect the dummy antenna (see note in a above) in series with the radio frequency ammeter to the transmitter.
(5) Place the TONE CW VOICE switch on CW.
(6) Set the MO TUNING and PA TUNING controls for the center of the frequency band in accordance with data on the calibration chart. (2,250 kc. when tuning unit TU-5-A is employed, or 3,750 kc. when tuning unit TU-6-A is employed.)
(7) Turn the transmitter OFF ON switch to the ON position.
(8) Tune the antenna circuit to resonance as prescribed in paragraph 256(1) (Z) to (o), inclusive, using the 0-1, r. f. ammeter in the dummy antenna to provide the indication of resonance.
(9) Adjust the control marked PA TUNING until the 0-1, r. f. ammeter in the dummy antenna circuit indicates a maximum current in the dummy antenna.
(10) Remove the calibration chart by turning the four knurled screws at the comers.
(11) Unlock the neutralizing capacitory lock by turning, with a screw driver, the lock to the left one quarter turn.
80
TM 11-273
RADIO SETS SCR—193—A, ETC. 35-36
(12) Rotate the neutralizing capacitory control until the current, as read by the radio frequency ammeter in the dummy antenna, is reduced to zero.
(13) Slightly readjust the antenna and power amplifier circuits to be sure that they are on resonance. If the ammeter in the dummy antenna shows an increased reading, repeat the operations (8) through (12).
(14) Lock the final position of the neutralizing capacitor adjustment, replace the calibration chart, and restore the transmitter for normal operation. The tuning units will each be neutralized when the neutralizing capacitor is approximately one-half engaged.
c. Speech amplifier grid bias adjustment.—The grid bias on the speech amplifier in radio transmitter BC-191-A is adjusted by the manufacturer and seldom requires readjustment in the field. The adjustment is not critical. Should the initial setting become displaced, remove the tube compartment, and set the S. A. BIAS control between 5 and 6.
d. Calibration reset.—The calibration of the transmitters should be checked periodically, employing the frequency meter SCR-211-A for the purpose. It is most important that the calibration be checked whenever the master oscillator tube is changed. If the check indicates that the transmitter varies more than 25 kilocycles from the frequency indicated on the calibration chart, the oscillator frequency should be adjusted as follows:
(1) Warm up the transmitter for at least 30 minutes, with the antenna tuned for rated output, prior to adjusting.
(2) Set the frequency meter SCR-211-A to 3000 kc. when transmitter tuning unit TU-5-A is used, or 4500 kc. when transmitter tuning unit TU-6-A is used.
(3) Adjust the transmitter for operation on c. w. at a frequency of 3000 kc. or 4500 kc., as the case may be, as prescribed in paragraph 256(1). Use data from the calibration chart for the setting on the control MO TUNING, and approach this setting from the lower dial readings.
(4) Open the calibration reset port located to the right of the TEST KEY (fig. 2), and with a screw driver, adjust the calibration reset capacitor 1104 until the transmitter zero beats with the frequency meter.
(5) Close the calibration reset port.
36. Normal current, resistance, and voltage readings.—The following normal current, resistance, and voltage readings are furnished for the information and guidance of servicing personnel. (The values
296642°—41---6
81
TM 11-273
36
SIGNAL CORPS
are approximate and will vary slightly with different sets and different measuring equipments.
a. Current readings.—(1) The current consumptions of the receiver and transmitter measured at the vehicular storage battery are listed in (a) below. The voltages listed are measured at the battery. Where the voltage supplied is 14.2 volts, the vehicular storage battery generator is operating (vehicular motor running).
(a) Radio receivers BC-312 and BC-S12-C.
Receiver Voltage (volts) (Current amperes)
Heaters off Heaters on
BC-312 112 [14. 2 4. 2 4. 6 7. 4 8. 1
BC-312-C (12 [14. 2 4. 2 4. 6 | No heaters
(6) Radio transmitters BC-191-A and BC-191-C.
Battery voltage (volts) Current (amperes)
Total Filaments
C. w. Tone and voice C.w. Tone and voice
14.2 39. 4 56. 9 8. 1 14. 9
(2) The following table gives the current and voltage readings at the terminals of the dynamotors BD-77-A and BD-77-B for three values of load current.
Caution.—Do not operate this equipment with the high voltage leads exposed.
Input Output
Volts Amperes Volts Milliamperes
14 14 -15 1 140-1 160 o
14 30 -32 5 1 070-1 090 990
14 40. 5-43. 5 1, 025-R 050 350
Note.—The input current above includes that taken by the starting relay.
82
TM 11-273
RADIO SETS SCR—198—A, ETC. 36
b. The normal voltage readings for radio receivers BC-312 and BC-312-C.—The tables of voltages shown below are provided for the information and guidance of servicing personnel. The readings are made at the tube prongs using the set analyzer of test set I-56-A, with an input voltage of 14 volts, the OFF MVC AVC switch in the MVC position, and the VOL control turned to maximum. For the c. w. oscillator readings, the CW OSC OFF ON switch is in the ON position. For all other readings this switch is in the OFF position. Adapter FT-211 must be used when the set analyzer of test set 1-56-A is employed for measurement on the two r. f. and first detector tubes. The plug of the adapter is inserted into the tube socket and its grid stud connected to the receiver grid clip. The socket end of the adapter is connected to the set analyzer plug, and the grid clip on the adapter is connected to the stud on the set analyzer plug. Measurements are then made in the regular manner.
Tube Voltages (volts)
Filament Cathode to ground Screen grid to ground Plate to ground
1st r. f. amplifier (VT-86) 6. 5 3. 5 92 207
2d r. f. amplifier (VT-86) 6. 5 3. 3 82 217
1st detector (VT-87) 6. 5 2. 5 77 217
1st i. f. amplifier (VT-86) 6. 5 3. 6 94 215
2d i. f. amplifier (VT-86) 6. 5 3. 7 97 217
C. w. oscillator (VT-65) 6. 5 100
Diode; 1st audio (VT-88) 6. 5 6. 7 — 215
2d audio amplifier (VT-66) 6. 5 18. 5 222 212
Band A 6. 5 20 — 106
Band B 15 — 102
R. f. oscillator Band C 12 — 104
(VT-65) Band D 0 — 98
Band E 0 — 95
Band F 0 — 97
c. Normal resistance values for radio transmitters BC-191-A and BC-191-C.—(1) General.—Normal resistance values obtained by point to ground measurements on the radio transmitters BC-191-A and BC-191-C, in a satisfactory condition, are indicated below. Use of these data in connection with similar measurements on faulty equipment, combined with a logical circuit analysis, will frequently disclose the source of trouble in inoperative or improperly operating
83
TM 11-273
36
SIGNAL CORPS
transmitters. The readings were taken under the following conditions, and similar conditions must be reproduced exactly if comparison measurements on a faulty transmitter are to be effected.
(a) All tubes and cords are removed from the transmitter.
(6) The pilot light LM-27 is removed.
(c) The CW TONE VOICE switch is set on VOICE.
(d) Tuning unit TU-5-A or TU-6-A is inserted.
(e) The OFF ON switch is in the ON position.
(/) A fuse FU-12 is in the active mounting.
(2) Measurements from tube sockets.—Tube socket connections, from which the measurements shown below are made, are numbered as shown in figure 36.
VT-4C
VT-25 I
—"V /\ \ / A
/ V4 Ax \
\cT w \ xA /
Front of socket shelf 71
Figure 36.—Transmitting vacuum tube socket pin locations.
Stage Tube Tube socket pin
1 2 3 4
Speech amplifier. VT-25 80 ohms.. 1 megohm .2-.203 megohm. 1 ohm.
Master oscillator. VT-4C 1 megohm. 80 ohms.. .2075 megohm.. 0 ohm.
Power amplifier. _ VT-4C 1 megohm. 80 ohms.. .21 megohm 0 ohm.
Modulator VT-4C 1 megohm. 80 ohms.. .203-. 206 megohm. 0 ohm.
(3) Measurements from cord sockets.—The socket pins from which measurements of resistance to ground are made are identified by number as shown in figure 37. This figure represents the cord connecting sockets for radio transmitters BC-191-A and BC-191-C as viewed from the outside of the set. Sockets are easily identified by the number and arrangement of the pins therein. Resistance measurements from these socket pins to ground are indicated below.
84
TM 11-273
36-37
RADIO SETS SCR-193-A, ETC.
SO-41 for PL’61
45 ^4^ ^\4'57
/ Cy*——Locating Pin
46-fO - o' _
A r\ / SO-39 for PL-59 SO-54 for PL-74
zk n "X/-7/
s4 <7 r \^6/ Co o\
SO-44 for PL’64 \ ) I )
32 \ / \JO Cl/
/b oK 69 —70
22-K)
\ O Q cT/~ Locating Pin
21
33 TL-2246
Figure 37.—Cording socket pin nomenclature.
SO-44 for PL-64
Pin No. Resistance to ground
34 100 ohms
*23 60-240 ohms..
23 Open
24 0 ohm
32 0 ohm
22 Open
21 Open
2 33 32 ohms 61 ohms
91 ohms .122 ohms
SO-41 for PL-61
Pin No. Resistance to ground
45 85 ohms _
46 85 ohms _
54 85 ohms
47 0 ohm
53 0 ohm
56 0 ohm
57 0 ohm
>55 .210 megohm
SO-54 for PL-
74
SO-39 for PL-59
Pin Resistance Pin Resistance No. to ground No. to ground
68 0 ohm 61 1 megohm
69 0 ohm
70 120 ohms_
71 95 ohms__ —
i INPUT LEVEL set at 0 gives 240 ohms, and set at 10 gives 60 ohms with intermediate values of resistance for other settings of the control.
3 Side tone adjustment (stepwise) values, keying relay manually operated.
0—Zero resistance.
37. Procedure in case of set failure.—a. Do not change fuses or make repairs with the high voltage on. Failure of this radio equipment to operate properly is usually due to worn, broken, or disconnected cords, plugs or sockets, run-down storage battery, worn dynamotor
85
TM 11-273
37-38 SIGNAL CORPS
brushes, defective fuses, or defective tubes. When set failure is encountered, these items should be checked before initiating a detailed check of component parts. If failure of both transmitter and receiver occurs simultaneously, the trouble is usually in the primary power source of leads connected thereto. If only one component fails to operate, determine, if feasible, if it is receiving proper supply voltages. This usually determines whether the trouble is inside or outside of the component. Check fuses in the equipment at an early stage in “trouble shooting.” Do not continue to burn out fuses before looking elsewhere to determine the basic source of trouble.
b. When exposed to conditions of excessive humidity, failure to operate properly may occur as the result of moisture accumulations across insulators or insulating structures. Every precaution should be taken to keep these installations moisture free.
Caution.—Many of the unit parts comprising these transmitters and receivers are readily damaged by excessive or abrupt applications of heat. A free flow of warm air through a chassis will accomplish the desired drying in less time than the application of very warm air without a free flow through and subsequently out of a chassis.
38. Locating trouble.—The following causes of set trouble may be present in the event that the component fails to function properly:
a. Radio receivers BC-312 and BC-312-C.
Symptom Cause
(1) No filament voltage Poor battery. Open power lead. Short circuited power lead. Poor plug contact. Burned-out fuse. Burned-out tube filament. Damaged bypass capacitor. Loose connection inside of the receiver.
86
TM 11-273
38
RADIO SETS SCR—193—A, ETC.
The first five of the above causes should be checked before removing the receiver chassis from its cabinet.
Symptom Cause
(2) No plate voltage Poor battery. Open or shorted cord. Poor plug contact. Burned-out fuse. Defective dynamotor. Defective filter.1 Loose connection inside of the receiver. Shorted bypass capacitor. Open resistor.
1 To check, remove the brush lead from terminal 2 of dynamotor terminal strip (see fig. 35) and check the actual brush voltage. If normal (or high) voltage is read, connect the brush lead to the lead removed from the terminal B. If receiver operates, the filter is damaged.
The first four of the above causes should be checked before removing the receiver chassis from its cabinet.
Symptom Cause
(3) No audio frequency output. Headset plug not completely inserted in jack. Defective headset, headset plug, or headset cord. Defective tube.2 Loose connections inside of the receiver. Damaged capacitor. Damaged resistor. Defective jack insulation. Breakdown on r. f. coils, leads, or switches. Defective band-change switch.
* Tubes used in these receivers should be checked with the tube checkers of test set 1-56-A at least once a year. If found serviceable, they should be replaced in the identical sockets of the same receiver from which they were removed.
87
TM 11-273
38
SIGNAL CORPS
The first two causes should be checked before removing the receiver chassis from its cabinet. The last two causes will be indicated by lack of signal audio output, although some audio noise output is present.
Symptom Cause
(4) No change in intensity of noise level when SEND REC switch is on SEND position and the transmitter is being keyed. (5) Erratic noise in receiver Antenna relay inoperative. Defective headset or headset cord. Defective dynamotor. Temperature controls chattering (BC-312 only).3 Antenna relay chattering. Dust or dirt in the receiver. A loose connection in the receiver. Defective tube. Defective capacitor or resistor in receiver.
8 This cause of trouble may be located or eliminated by operation of the HEATERS OFF ON switch and is found only in the BC-312.
The first possible cause of trouble should be checked before removing the receiver chassis from its cabinet.
Symptom Cause
(6) A. c. ripple in output Defective filter choke. Defective filter capacitor. Defective dynamotor.
(7) Ignition noise Defective chassis grounding. Defective noise antenna. Defective vehicle bonding.
(8) Frequency calibration off Improper alinement.4
4 See paragraph 39.
88
TM 11-273
38
RADIO SETS SCR—19 3—A, ETC.
Symptom Cause
(9) Lack of sensitivity Improper alinement.1 Worn out tubes.
4 See paragraph 39.
b. Radio transmitters BC-191-A and BC-191-C.
Symptom Cause
(1) No filament voltage Poor battery. Open power lead. Short-circuited power lead. Defective TONE CW VOICE switch. Poor plug contact. Burned-out fuse. Damaged bypass capacitor. Dynamotor starting relay not functioning properly. Loose connection inside of the transmitter. Open interlock.
(2) No plate current Poor battery. Open or shorted cord. Poor plug contact. Burned-out fuse. Defective dynamotor. Loose connection inside of the transmitter. Shorted bypass capacitor. Open resistor. Damaged choke coil.
(3) No r. f. output Damaged master oscillator or power amplifier tubes. Damaged choke coil. Damaged coupling capacitor. No plate voltage. Excessive bias voltage, open grid. Output terminal strip not properly connected. Damaged antenna ammeter. Inoperative antenna switching relay and contacts. Defective TONE CW VOICE switch.
89
TM 11-273
38-39
SIGNAL CORPS
Symptom Cause
(4) No voice modulation Damaged speech amplifi er or modulator tubes. Improper modulator bias. Defective speech amplifier bias. Microphone plug not properly in jack. Bad plug contacts. Defective microphone. Defective microphone cord. Defective microphone filter circuit. Damaged transformers. Open resistor.
(5) No tone modulation Damaged speech amplifier or modulator tubes.
Improper modulator bias. Defective speech amplifier bias. Defective TONE CW VOICE switch. Damaged resonating capacitors. Defective transformers.
(6) No side tone Open resistor. Damaged transformer. Open resistor. Damaged speech amplifier tube. Damaged microphone or microphone circuits. Bad plug connections. Damaged resonating capacitors.
Note.—The bias voltages for the modulator tubes and the speech amplifier tube are derived from the grid resistor system of the power amplifier tube, and anything which will affect the proper operation of the power amplifier tube grid bias will affect the biasing of the audio frequency stages.
39. Repairs.—Repairs other than the following will ,not be attempted by using personnel unless specifically authorized under the provision of Appendix C, Signal Corps General Catalog:
a. Cords.—Cords may become defective because of an open circuit in one or more conductors, a short circuit between two or more conductors, or between any conductor and ground. These defects most frequently occur at the point of attachment of the cord to its corresponding plug. These points should be examined and where possible necessary repairs made. In the event that the damage occurs any great distance from either end of the cord, it is normally impossible to make a serviceable permanent repair of the cord. A new cord should be obtained and installed. However, in an emergency, the defective portion of the cord may be cut out and jumpers used to restore the necessary circuits until a new cord can be obtained. Cords CD-261 and CD-262 are concentric transmission lines each consisting of flexible shielded conduit containing an inner conductor supported by a
90
TM 11-273
39-40
RADIO SETS SCR-193-A, ETC.
series of spaced insulating beads. These cords may be damaged by crushing or bending sharply. If it is found necessary to attach a terminating fitting or a concentric transmission line, before cutting the shield or conductor to length, the shield should be forced to its shortest length, and the conductor should be pulled tightly to straighten out any kinks. Temporary repair may sometimes be made by careful shaping to hold the inner conductor away from the outer shield. If these cords have been badly damaged, and the conductor cannot be straightened, they should be replaced as soon as practicable.
b. Headsets.—The failure of a headset to operate properly is usually due to a defective cord or plug which may be reparable. However, if the damage is within the phones, a new headset should be secured and the defective unit shipped to the proper agency for repair.
c. Dynamotors DM-17-A and DM-21-A.—Normally, if these dynamotors have become defective, they should be removed and replaced. Replacements are obtained through the usual channels. The replacement of brushes, turning down of commutators, freeing of bearings, and all repairing of defective receiver dynamotors is done at Signal Corps repair shops or Signal Corps radio sections at air depots. In event the dynamotor cannot be replaced, or where an emergency requires it, local repairs are allowable. Where local repairs are made, careful sanding-in of new brushes to fit the commutator, proper spring adjustment, and a running-in period are necessary to insure quiet receiver operation. If results following local replacement of brushes are unsatisfactory, the dynamotor should be returned to a depot for overhaul when it can best be spared. Commutators not unduly worn may be cleaned by using a fine grade of sandpaper and/or wiping off thoroughly with carbon tetrachloride. If the bearings are not damaged, but merely need freeing, a drop of light oil is added to each. If the trouble is due to an open or short-circuited winding, grooved commutators, or some other serious defect, the dynamotor should be replaced.
d. Dynamotor units BD-77-A and BD-77-B.—The probable causes of trouble in these units are loose or defective brushes, locked or damaged bearings, dirty or undercut commutator, open or short-circuited windings. These should all be checked and treated in the same manner as described in c above.
Section V
LISTS OF PARTS
Paragraph
Components, weights, and dimensions-------------------------------- 40
Replaceable parts-------------------------------------------------- 41
91
40. Components, weights, and dimensions.—Dimensions and weights, where unappreciable, are omitted
SCR- SCR- SCR- SCR- SCR- . , Dimensions (inches) Unlt
193-A 193-B 193-C 193-D 193-E Article weight
Height Width Depth Length (pounds)
erer
2 2 2 --------- Adapter FT-177-A6_________ % 2 2 ______ 0. 09
1 1 1 1 1 Box BX-8------------------- 9% 8% 7%__________ 6. 25
1 1 1 1 1 Box BX-19------------------ 1% 12)4 4%__________ 2. 5
1 ---- 1 1 ---- Box BX-21----------------- 13% 10 11%_________ 2.5
4 4 4 4 4 Brush BR-5; spare (includes spring)________________ .01
4 4 4 4 4 Brush BR-6; spare (includes spring)________________ .08
2 2 2 --------- Brush, H. V., for DM-17-A (spare)_________1______”______
------------- 2 2 Brush, H. V., for DM-21-B (spare)_________________
2 2 2 --------- Brush, L. V., for DM-17-A (spare)______________________~~
------------- 2--2 Brush, L. V., for DM-21-B (spare)_ ------------- 1 Cabinet CH-60________________________ 29% 53% 11%_________ 11111 Case CS-48 (for transmitter tuning unit) _ _ 8 16% 8 __________ 4.37
1 ---- 1 ----------- Conduit CT-4_____________________________ 2 %_______
-------- 1 ----------- Connector, bulkhead___________________________ 1
1 1 1 --------- Control box BC-321, including cord CO- 3 5 4 ______ 1. 0
173
1 ---- 1 ----------- Cord CD-205_■____________________________ 30 ______ .84
--- 1 ------------- Cord CD-206_____*________________________ 36 ______ .87
1 ---- 1 _______-___ Cord CD-221______________________________ 30 ___I”______
----------------- 1 Cord CD-226_________________________________ 48 ______ .84
1 ---- 1 ---------- Cord CD-261_______________________________ 108 _____ 2. 7
--- 1 ------------- Cord CD-262______________________________ 146 _____ 3. 5
1 ---- 1 ----------- Cord CD-269________________________•_____ 30 ______ .81
--- 1 ------------ Cord CD-277______________________________ 96 15
1 ---- v 1 --------- Cord CD-288______________________________ 30 ______ .5
TM 11-273
40 SIGNAL CORPS
92
RADIO SETS SCR—19 3—A, ETC.
TM 11-273
40
93
_____1 ________________ Cord CD-290____ 36 ___________________________________ .56 ____ 1 _____________ Cord CD-292____ 36 ___________________________________ .90 ____ 1 _____________ Cord CD-295________________________________ 96 _______ 1. 4 ____ 1 _____________ Cord CD-297____ 105 __________________________________ 1. 1 1 1 ____________ Cord CD-314____ 30 ___________________________________ .7
2 ____ 2 ___________ Cord CD-318 (for microphone T-30-A)_________ 84 -------'------
____ 1 ________________ Cord CD-320________________________________ 9 _______ ____ 1 ________________ Cord CD-346________________________________ 8 _______ ____ 1 ____ Cord CD-3585________________________________________ 36 ______ .70 1 1 ________ 1 Cord CD-3594_________________________________ 30 ______.62
_________ 1 Cord CD-410__________________________________ 60 _______ _________ 1________1 Cord CD-411_____________________________ 66 ______________ _________ 1 Cord CD-440______________________________________ 48 ______________ 1 _______ 1 _____,_ Cord CO-165-A____________________________ 18 ______________ .37
_____ 1 Cord CO-170-A______________________________________________ 60 L _____ 1 _____________ Cord CO-175-A______________________________ 63 .72 _____ 1 _______________ Cord CO-189________________________________ 66 11111 Cover BG-67 (for mast base MP-37)____________________________ 12 3_.5
1111 _______________ Cover BG—75_________________ 8 19 10 __________ 1.25
1 1 1 1 ____ Cover BG-78_________________ 22 24 10 __________ 1. 12
1 1 1 1 ____ Cover BG-79_________________ 11 12 8 __________ .5
______________ 1 ______I Cover BG-84________________ 25% 43% 10%___u______________
Dynamotor BD-77-A, including— 2 Brush BR-5. 2 Brush BR-6. 1 Fuse FU-13. 1 1 1 ________ 2 Fuse FU-18 (1 in use). 11 11 7%__________ 37.3
1 Fuse FU-22.
6 Fuse link M-141 (spares).
6 Fuse link M-168 (spares).
1 Mounting FT-107.
। 1 Wrench, setscrew.
See footnotes at end of table.
TM 11-273
40 SIGNAL CORPS
40. Components, weights, and dimensions—Continued.
Dimensions (inches)
SCR- SCR- SCR- SCR- SGR- . ------------------------ Unit
193-A 193-B 193-C 193-D 193-E J Article ' weight
Height Width Depth Length (Pounds)
(Dynamotor unit BD-77-B, including—
2 Brush BR-5.
2 Brush BR-6.
1 Fuse FU-13.
-------------- 1 1 2 Fuse FU-22. > 11 11 7%__________ 37.3
6 Fuse link M-141 (spares).
6 Fuse link M-168 (spares).
1 Mounting FT-107.
1 Wrench, setscrew.
2 2 2 2 2 Fuse FU-13_________________________________ 2 % .05
2 2 2 2 ____ Fuse FU-18_________________________________ 3 J/2 .01
2 FuseFU-18-A8____________________ 3 14 .01 4 4 4 ---- Fuse FU-21______________-______________________ 1% yt . 01
4 4 FuseFU-21-A8______________________________ iy y^ .01 2 2 2-2 2 Fuse FU-22________________________________ 3 i3^6 . 13
2 2 2 2 2 Head set P-19_______________ 2 6 6 __________ 1. 12
2 2 2 -------- Instruction Book for Radio Sets BC-193- _____________________
A, BC-193-B, and BC-193-C.
2 2 2 -------- Instruction Book for Radio Transmitter ______________________
BC-191-A.
-------------- 2 Instruction Book for Radio Set BC-193-D__________1___________ -------------- 2 Instruction Book for Radio Set BC-193-E________________ -------------- 2--2 Instruction Book for Radio Transmitter _______________
I BC-191-C. I
TM 11-273
40
RADIO SETS SCR-19 3-A, ETC.
2 2 Instruction Book for Radio Receivers '---.-----------------------
BC-312-C and BC-324-C.
_______________ 2 ___ Instructions for Radio Installation in -)------------_----------
Scout Car M3A1.
____________________ 2 Instructions, Radio Installation in Truck, ------------------------.
%-ton, Command Radio.
__________ 2 Insulator IN-89 (spare)---------------------------------------------- -12 __________ 3__Insulator IN-98 -23 __________ 3_Insulator IN-101 • 23 __________ 2_____________Insulator IN-101; (1 in use, 1 spare)- -23 1 ________ 1 _______ Jack JK-34-A --------------------
1 _____ 1 ____________ Junction box 3___________________________________________________
1 1 1 1 1 Key J-45________________________________________________ 1- 09
2 2 2 2 2 Lamps LM-27--------------------------------------------- -05
11111 Mast base MP-37 2_____________________________________________ 10% 7% 10.5
_________z 1 Mast base bracket MP-41 2________2 2 2_2 Mast section MS-49 (1 in use, 1 spare)---------- 35 %_________.16
2 2 2 2 2 Mast section MS-50 (1 in use, 1 spare)---------- 36 % .38
2 2 2 2 2 Mast section MS-51 (1 in use, 1 spare)------- 36 % . .48
2 2 2 2 2 Mast section MS-52 (1 in use, 1 spare)---------- 36 % .66
2 2 2 2 2 Mast section MS-53 (1 in use, 1 spare)---------- 36 % .81
____ 2 _____ 2 2 Microphone T-17_______________ 6 2 2 ----------.■ .88 2 2 Microphone T-30-A 7____________
11111 Mounting FT-151-B_________________________________________________________________
11111 Mounting FT-172_______________ 2% 2/2 1 __________ .25
11111 Mounting FT-178_______________ 2/2 2% 1 __________ .25
1 _____ 1 _____r______ Mounting plate FT-176_________ 10% 34% % __________ 8-75
____ 1 _______________ Radio control box BC-309, including— 3% 3% 2% --------- .40
1 LM-27.
See footnotes at end of table.
95
TM 11-273
40
SIGNAL CORPS
40. Components, weights, and dimensions.—Continued.
Dimensions (inches)
SCR- SCR- SCR- SCR- SCR- .... , ----------T______________ Unit
193-A 193-B 193-C 193-D 193-E Article weight
Height Width Depth Length Uiam- (pounds)
Radio receiver BC-312, including—
1 Dynamotor DM-17-A.
Ill -----------------< 3 Fuse FU-21 (2 in use, 1 spare). > 9% 18 7 _______ 40
2 Lamp LM-27.
1 Mounting FT-162.
Radio receiver BC-312-C, including—
1 Dynamotor DM-21-B.
-------------- 1 1 < 3 Fuse FU-21-A (2 in use, 1 spare). > 10% 18 19 ___ 40
2 Lamp LM-27.
1 Mounting FT-162.
(Radio transmitter BC-191-A (less mount- '
ing FT-151-A), including—
3 Fuse FU-12.
1 Lamp LM-27.
1 1 1 --------- 1 Socket cap M-163-A. 20% 23« »«• --------- “.75
1 Socket cap M-164-A.
2 Socket cap M-165-A.
I 2 Wrench, setscrew.
96.
[Radio transmitter BC-191-C (less mounting FT-151-A), including—
3 Fuse FU-12-A (1 in use, 2 mounted spare).
________________ 1 1 1 Lamp LM-27. ? 20% 23% 9%6____________ 55. 75
1 Socket cap M-163-A.
1 Socket cap M-164-A.
2 Socket cap M-165-A.
2 Wrench, setscrew.
11111 Roll BG-56 (or roll BG-56-A for SCR- ______________________________ 28 1% 2. 5
193-D and SCR-193-E).
1 set 1 set 1 set 1 set 1 set Screws, nuts, and lockwashers (for respective radio sets).
1 1 1 __________ Shield M-191__________________________________________________________
__________ 1 ______________ Shield MP-38 (for MP-37)_________________________-----------------------1________________________1 Socket cap M-163-A________________________________
2 Spacers for control box BC-321_________'----------------------- 2 1_2 1 1 Terminal block TM-183___________ 1% 5% 1 ----------- 0. 5
11111 Transmitter tuning unit TU-5-A____________________ 7% 16% 8%--------.--- 14. 43
11111 Transmitter tuning unit TU-6-A-------------------- 7% 16% 8%------------ 12. 43
8 8 8 8 8 Tube VT-4-C (4 in use, 4 spare)__________________ 8 2% 0. 44
2 2 2 2 2 Tube VT-25 (1 in use, 1 spare) __---------------- 5% 2% 0. 13
4 4 4 4 4 Tube VT-65 (2 in use, 2 spare)_______________________________ 0. 1
2 2 2 2 2 Tube VT-66 (1 in use, 1 spare)_______1_______________________ 0. 1
8 8 8 8 8 Tube VT-86 (4 in use, 4 spare)_______________________________ 0. 1
2 2 2 2 2 Tube VT-87 (1 in use, 1 spare)_________________________________ 0.1
2 2 2 2 2 Tube VT-88 (1 in use, 1 spare)______________,------------------- 0. 08
Feet Feet Feet Feet Feet
20 20 20 20 20 Wire W-128___-_______________________________________________________
40 _____ 40 ____________ Wire W-131____________________________________________________________
20 _____ 20 ____________ Wire W-132____________2_______________________________________________
296642°—41---7
97
See footnotes at end of table. 296042°— 1——7
TM 11-273
RADIO SETS SCR—19 3—A, ETC. 40
98
TM 11-273
40 SIGNAL CORPS
40. Components, weights, and dimensions—Continued. . । _____
Dimensions (inches)
SCR- SCR- SCR- SCR- SCR- . . -------------------------— Unit
193-A 193-B 193-C 193-D 193-E Article weight
Height Width Depth Length Uiam- (pounds) ctcr
Feet Feet Feet Feet Feet
10 ----. 10 ___________ Wire W-133__________.____________________________________________
10 --- 10 ------------ Wire W-134_______________________
10 ---- 10 ___________ Wire W-135___________________________________12 1111211 1111Z IZ ” Z
10 ____ 10 ____________ Wire W-136________________________
10 ____ 10 ____________ Wire W-137_____________________________________________’
10 ____ 10 ____________ Wire W-138____________________________________ _ f
10 ____ 10 ____________ Wire W-139______________________________
10 ____ 10 ____________ Wire W-140_______________________________________________’ ’ ’ ’
1 In SCR-193-A and SCR-193-C, adapter FT-177 may be substituted for adapter FT-177-A.
2 Mast base MP-14 or MP-14-A and shield MP-33 may be substituted for mast base MP-37 and shield MP-38. The shielc
MP-14 or MP-38 is used on the SCR-193-C only.
3 Sets of this type issued prior to September 1, 1939, required one junction box (no type number) furnished by the Ordnance Department, one terminal block TM-183 and jack JK-3L-A (or JK-34) furnished by the Signal Corps in lieu of one junction bo>
TM-188 which is an assembly of these units.
4 In SCR—193—A and SCR—193—C, cord CD—289 may be substituted for cord CD—359 in sets of this type issued prior to Septembej
1, 1939.
5 In SCR-193-B, cord CD-291 may be substituted for cord CD-358 in sets issued prior to September 1, 1939.
6 In SCR-193-B, adapter FT-177 may not be substituted for adapter FT-177-A.
7 Microphone T-17 may be substituted for microphone T-30-A, in which case cord CD-318 is not used.
8 Fuses FU-18 and FU-21 may be substituted for FU-18-A, and FU-21-A respectively. The “A” series have a longer time delay.
RADIO SETS SCR-193-A, ETC.
TM 11-273
41
99
41. Replaceable parts.—a. Radio receiver BC-312.
R ef eren ce No Stock No. Name of part Description Function Drawing No.
Ci-_.--- 3D289- Capacitor CA—289__ . Variable air; 3-25 nA_ Band A trimmer 1st r. f_ SC-A-1728
C2----- 3D291-- Capacitor CA-291- Variable air; 6-100 nA____ Band B trimmer 1st r. f_ SC-A-1728
C3----- 3D291-- Capacitor CA—291_ Variable air; 6-100 nA____ Band C trimmer 1st r. f_ SC-A-1728
C4----- 3D290-- Capacitor CA-290- Variable air; 4-50 nA_ Band D trimmer 1st r. f_SC—A-1728
C5----- 3D290-- Capacitor CA-290- Variable air; 4-50 nA_____ Band E trimmer 1st r. f_ SC-A-1728
C®_-_-- 3D290-- Capacitor CA-290- Variable air; 4-50 nA_____ Band F trimmer 1st r. f_ SC-A-1728
C7----- 3D289-- Capacitor CA-289— Variable air; 3-25 nA__ Band A trimmer 2d r. f__ SC-A-1728
C8----- 3D291- Capacitor CA-291- Variable air; 6-100 nA_ Band B trimmer 2d r. f__ SC—A—1728
Co----- 3D291-- Capacitor CA-291- Variable air; 6-100 nA_ Band C trimmer 2d r. f__ SC-A-1728
C10----- 3D290--- Capacitor CA-290-,- Variable air; 4-50 nA_ Band D trimmer 2d r. f__ SC-A—1728
Cn—.---- 3D290- Capacitor CA-290_ Variable air; 4-50 nA_____ Band E trimmer 2d r. f_ SC—A—1728
C12---- 3D290- Capacitor CA-290-- Variable air; 4-50 nA___ Band F trimmer 2d r. f______ SC-A-1728
C13---- 3D289- Capacitor CA-289-- Variable air; 3-25 nA____ Band A trimmer 1st det_____ SC-A-1728
C14---- 3D291- Capacitor CA-291-- Variable air; 6-100 nA__ Band B trimmer 1st det_____ SC-A-1728
C15---- 3D291-- Capacitor CA-291-- Variable air; 0-100 nA_ Band C trimmer 1st det_ SC-A-1728
Cio---- 3D290- Capacitor CA-290-- Variable air; 4-50 nA__ Band D trimmer 1st det_ SC-A-1728
C17---- 3D290-- Capacitor CA-290-- Variable air; 4-50 nA__ Band E trimmer 1st det_ SC-A-1728
Cis---- 3D290-- Capacitor CA-290-- Variable air; 4-50 nA-------- Band F trimmer 1st det_ SC-A-1728
Ci9_:--- 3D2§9- Capacitor CA-289- Variable air; 3-25 nA_._ Band A trimmer r. f. osc_____ SC-A-1728
C2o---- 3D291-- Capacitor CA-291_ Variable air; 6—100 nA__ Band B trimmer r. f. osc_____ SC—A—1728
C21---- 3D291- Capacitor CA-291-- Variable air; 6-100 nA_ Band C trimmer r. f. osc_____ SC—A-1728
C22---- 3D290- Capacitor CA—290_ Variable air; 4—50 nA_•_ Band D trimmer r. f. osc_____ SC—A—1728
C23---- 3D290- Capacitor CA-290_ Variable air; 4-50 nA_ Band E trimmer r. f. osc_ SC-A—1728
C24---- 3D290- Capacitor CA-290- Variable air; 4-50 nA_ Band F trimmer r. f. osc_ SC-A-1728
C26----- 3D294--- Capacitor CA-294_ Fixed air; 125 nA___ Padder 1st r. f_________ SC-D-2575
C26----- 3D293--- Capacitor CA-293- Variable air; 10-210 nA_- Antenna alinement__ SC-A-2580
TM 11-273
41
SIGNAL CORPS
100
a. Radio receiver BC-312—Continued.
-Rof cren ce No. Stock No. Name of part Description Function Drawing No.
C27----- 3D284--- Capacitor CA-284- Molded, paper; 0.05 A.-400 v_ 1st r. f. bypass_ SC-D-1995
C28----- (i)----- Capacitor-------- Ganged with C34, C46, C82; 1st r. f. tuning______________ SC-D-2568
13-226 MMf.
C29-----I encased!0’05 ^f-~300 v- lst r- f- cathode bypass----- SC-D-512
C30------3D195--- Capacitor CA-195.' ■ unit 9.05 mC-300 v_ 1st r. f. screen bypass_________ SC—D—512
C3i----- e u 0.05 /if.-300 v_ 1st r. f. “B” supply bypass___________________________ SC-D-512
C32----- 3D284-- Capacitor CA-284- Molded paper; 0.05/tf.—400 v._ 1st r. f. plate bypass_____ SC—D—1995
C33----- 3D266-- Capacitor CA—266:- Mica; 100 /i/if_____ 2d r. f. grid coupling______________ SC—D—1993
C34----- f1)--.- Capacitor--------- Ganged with C28, C46, C82; 13- 2d r. f. tuning_ SC-D-2568
226 /i/if.
C35— ---1 (MetalencasedfO.05/if.-300 v__ 2d r. f. cathode bypass____ SC-D-512
C36-----13D195--- Capacitor CA-195-\ as j 0.05/if.-300 v 2d r. f. screen bypass. ___ SC—D-512
C37-----J I one unit 10.05 /if .-300 v._ 2d r. f. “B” supply bypass_ SC-D-512
C38----- 3D294- Capacitor CA-294... . Fixed air; 125 w*f_ Padder, lst det_________ SC-D-2575
C39----- 3D284- Capacitor CA-284--- Molded, paper; 0.05 /if.-400 v_ 2d r. f. plate bypass_ SC-D-1995
C40----- 3D294- Capacitor CA-294__ Fixed air; 125 /i/if_ Padder, r. f. osc____________ SC-D-2575
C4i----- 3D278- Capacitor CA—278--- Mica; 5 /i/if----------- C. w. osc. coupling____ SC—D—1993
C42----- 3D300- Capacitor CA—300-- Mica, aged; 3,000 ______ Band C padder r. f. osc_ SC—D—1993
C43----- 3D297- Capacitor CA—297-- Mica, aged; 1,600 /z/if_ Band B padder r. f. osc_ SC—D—1993
C44----- 3D299-- Capacitor CA-299-- Mica, aged; 750 /i/if--- Band A padder r. f. osc_ SC-D-1993
C43----- 3D266-- Capacitor CA—266-- Mica; 100 /z/if--------- 1st det. grid coupling_ SC—D—1993
C46----- (i)------ Capacitor------- Ganged with C28, C34, C82; 13- lst det. tuning__ SC-D-2568
226 /i/zf.
C47----- 3D266--- Capacitor CA-266- Mica; 100 g/if--------1 R. f. osc. coupling______________ SC—D—1993
RADIO SETS SCR-19 3-A, ETC.
TM 11-273
41
101
C48-----1 (Metal encasedf0.05 pf.-300 v_ 1st det. cathode bypass_____ SC-D-512
C49-----pD195---- Capacitor CA-195_j as ] 0.05/zf.-300 v_ 1st det. screen bypass______________ SC—D-512
C50-----J I one unit 1.0.05 /zf.-300 v_ 1st det. “B” supply bypass SC-D-512
C51----- 3D323--- Capacitor CA-323_ Variable air, with shaft; 4-50 Crystal phasing____________ SC-A-1728
ju/zf.
C52----- 3D266-- Capacitor CA-266__ Mica; 100 ppi_________ 1st i. f. grid coupling_________ SC-D-1993
C53----- 3D296- Capacitor CA-296__ Mica, aged; 400 /z/zf_ 1st det., plate____________________ SC—D-1993
C54----- 3D281- Capacitor CA-281__ Molded, paper; 0.01 /zf.—400 v_ 1st det., plate bypass_ SC-D-1995
C55----- 3D295- Capacitor CA-295__ Mica; 50 nnf__________ 2d i. f. grid___________________ SC-D-1993
C56---— 3D281---- Capacitor CA-281_ Molded, paper; 0.01 jzf-_400 v_ 2d i. f. a. v. c. bypass__ SC-D-1995
C57----- 3D295--- Capacitor CA—295_ Mica; 50 /z/zf_____ 1st i. f. plate_______________________ SC—D—1993
C58----3D281----- Capacitor CA-281_ Molded, paper; 0.01/zf-400 v_ 1st i. f. plate bypass___ SC-D-1995
C59-----1 f Modification 10.05 /zf-_300 v__ 1st i. f. cathode bypass_ SC-D-2567
Ceo-----f3D302--- Capacitor CA-302_j of j 0.05 gf.-300 v__ 1st i. f. screen bypass____________ SC-D-2567
C8i-----J I CA-195 1.0.05 Azf-_300 v__ 1st i. f. “B” supply bypass SC-D-2567
C62----- 3D284- Capacitor CA-284___ Molded, paper; 0. 05 pf.-400 v_ 1st det. a. v. c. bypass_ SC-D-1995
C83----- 3D281- Capacitor CA-281___ Molded, paper; 0. 01 /zf.-400 v_ 1st i. f. a. v. c. bypass_ SC-D-1995
C84----- 3D295--- Capacitor CA-295_ Mica; 50 __________ Diode input____________________________ SC-D-1993
CM------ 3D295_ Capacitor CA-295___ Mica; 50 wzf_______ 2d i. f. plate_____________________ SC-D-1993
C88----- 3D281- Capacitor CA-281___ Molded, paper; 0. 01 juf-~400 v_ 2d i. f. plate bypass_ SC-D-1995
C87----- 3D279--- Capacitor CA-279_ Mica; 10 n/A_______ Diode a. v. c. coupling_ SC-D-1993
C88----- Modification 0. 05 /zf.—300 v__ 2d i. f. cathode bypass_______________________________ SC—D-2567
C89-----’3D301--- Capacitor CA-301_■ of 0. 05 /if.-300 v__ 2d i. f. screen bypass_____ SC—D-2567
C70----- CA-195 0. 05 /zf.-300 v__ 2d i. f. “B” supply bypass SC-D-2567
C71----- 3D218--- Capacitor CA-218_ Mica; 150 nnf______- Diode, r. f. bypass__________ SC-D-1993
C72_____ 3D193___ Capacitor CA-193_ Mica; 500 nA_______ Diode, r. f. filter____________________ SC-D-1993
C73----- Modification 0. 05/zf.-300 v _ _ Diode, cathode bypass_______________________ SC-D-2567
C74----- 3D301--- Capacitor CA-301_ of 0. 05 juf~300 v__ 1st audio plate bypass_______ SC-D-2567
C75_____ I CA-195 |o. 05 /zf—300 v._ A. v. c. filter bypass_ SC-D-2567
C78----- 3D281--- Capacitor CA-281_ Molded, paper; 0. 01 /zf.-400 v_ 2d audio coupling_ SC-D-1995
C77----- 3D295--- Capacitor CA-295_ Mica; 50 ggf________ 2d i. f. grid_________________ SC-D-1993
TM 11-273
41
SIGNAL CORPS
102
a. Radio receiver BC—312—Continued.
Reference stock No. Name of part Description Function Drawing No.
C78----j Metal en- 0. 1 4--400 v- Heater bypass________________ SC-D-512
C79---- 3D276---- Capacitor CA-276- cased as one 0. 1 4--400 v_ Heater bypass____________ SC-D-512
Cso---- unit 0. 1 Af.-400 v--------------------------------2d audio plate bypass_ SC-D-512
C8i---- 3D281- Capacitor C A—281--- Molded, paper; 0. 01 pi—400 v_ 1st audio coupling____ SC—D—1995
C82---- (»)--- Capacitor--------- Ganged with C28, C34, C46; R. f. osc. tuning_ SC-D-2568
13-226 M4-
C83---- 3D277- Capacitor CA-277_r— Molded, paper; 0. 1 4--400 v_ _ R. f. osc. plate bypass_ SC-D-1995
C84---- 3D280- Capacitor CA-280---- Variable aif, with shaft; 1-10 C. w. osc. tuning_ SC-A-1728
A*4-
Cm----- 3D253- Capacitor CA-253-- Variable air; 4-75 /x4_______ C. w. osc. trimmer___ SC-A-1728
; C88----- 3D266- Capacitor CA—266—__ Mica; 100 up!_____ C. w. osc. grid_____ SC—D—1993
) C87----- 3D284__ __ Capacitor CA-284- Molded, paper; 0. 05 4 -400 v_ C. w. osc. plate bypass_ SC-D-1995
C88---- 3D266- Capacitor CA—266-- Mica; 100 ju4________________ R. f. osc. grid____________ SC—D—1993
Css---- 3D211- Capacitor CA-211-- Mica; 0. 002 fit---- Thermostat contacts_______________ SC—D-1993
Coo---- 3D211- Capacitor CA-211-- Mica; 0. 002 /j.f--- Thermostat contacts_.- __ SC-D-1993
Coi--^- 3D295--- Capacitor CA-295-- Mica; 50^4_-_______________ 1st i. f. plate__________ SC-D-1993
Co2---- 3D295-- Capacitor CA—295- Mica; 50 ^4_________ Diode input_______________________ SC—D—1993
C93----- 3D295--- Capacitor CA-295- Mica; 50 m4_______ 2d i. f. plate______________________ SC-D-1993
C94---- 3D298- Capacitor CA-298-- Mica; aged; 800 ------------- Crystal filter input_ SC-D-1993
Cos---- 3D298- Capacitor CA-298---- Mica, aged; 800 m4--------- Crystal filter input_ SC-D-1993
Cfl6--- 3D286- Capacitor CA-286---- Mica; 75 m4_______ C. w. osc. filter_____________ SC-D-1993
C97---- 3D286- Capacitor CA—286-- Mica; 75 ju4________ C. w. osc. filter___________________ SC—D—1993
C98---- 3D275- Capacitor CA-275---- Paper; 4 4----------------- 2d audio cathode bypass____ SC-D-512
Coo---- 3D284- Capacitor CA-284-- Molded, paper; 0.05 4--400 v_ 2d r. f. a. v. c. bypass_ SC-D-1995
C100--- 3D294- Capacitor CA-294-- Fixed, air; 125 m4__ 2d r. f. padder______ SC-D-2575
Cun---- 3D266- Capacitor CA-266-- Mica; 100 m4-------- 1st r. f. grid coupling_ SC-D-1993
RADIO SETS SCR—193—A, ETC.
TM 11-273
41
103
C102---- 3D284__.— Capacitor CA-284- Molded, paper; 0.05 juf.-400 v_ 1st r. f. a. v. c. bypass_ SC-D-1995
CX------ 2Z3501-6— Crystal DC-6--- 470 kc------■_______ Crystal filter unit_ SC-A-1994
DM------ 3H1617A— Dynamotor DM-17-A_:__________________ D. c. power pack_______________________ SC—D—2576
Fi------ 3Z1921-- Fuse FU-21-------- 10 a.-25 v------- Dynamotor and filaments_______
F2----- 3Z1921-- Fuse FU-21-------- 10 a.-25 v______ R. f. osc. compart, heaters____
Ji----- 2Z5534-- Jack JK-34--------------------------- 1st audio phones__ SC-D-439
J2---- 2Z5534-- Jack JK-34--------------------------- 2d audio phones___ SC-D-439
J3---- 2Z5533-- Jack JK-33--------------------------- Speaker_____________ SC—D-483
J<----- 2Z5533--- Jack JK-33--------------------------- Microphone________ SC-D-483
J5----- 2Z5534___ Jack JK-34___________________________ Key_______________ SC-D-439
Li------ -------- Coil-------------------------------- Band A, 1st r. f_____ SC-D-2556
L2--------------- Coil------------,-------------------- Band B, 1st r. f____ SC-D-2556
L3--------------- Coil--------------------------------- Band C, 1st r. f__ SC-D-2556
L4--------------- Coil-------------------------------- Band D, 1st r. f___ SC-D-2556
L5--------------- Coil-------------------------------Band E, 1st r. f_____ SC-D-2556
L6--------------- Coil-----------------...------------ Band F, 1st r. f_____ SC-D-2556
L7--------------- Coil-----------------'-------------- Band A, 2d r. f______ SC-D-2556
Ls--------------- Coil--------------------------------- Band B, 2d r. f___ SC-D-2556
L9--------------- Coil-------------------------------- Band C, 2d r. f____ SC-D-2556
Lio-------------- Coil----------2---------------------- Band D, 2d r. f_____ SC-D-2556
Ln--------------- Coil--------------------------------- Band E, 2d r. f_____ SC-D-2556
L12-------------- Coil---------------------------------I Band F, 2d r. f____ SC-D-2556
Ln--------------- Coil-------------------------------- . Band A, 1st det____ SC-D-2556
L14-------------- Coil------------v----------------- Band B, 1st det________ SC-D-2556
L1S--’----------- Coil------------------------------ Band C, 1st det_x______ SC-D-2556
Li6-------------- Coil------------------------------- Band D, 1st det______ SC-D-2556
L17-------------- Coil__------------------------------ Band E, 1st det_____ SC-D-2556
Li8-------------- Coil--------------------------------- Band F, 1st det____ SC-D-2556
Lis-------------- Coil--------------------------------- Band A, r. f., osc_ SC-D-2556
L20-------------- Coil--------------------------------- Band B, r. f., osc_ SC-D-2556
L21-------------- Coil -------------------------------- Band C, r. f., osc_ SC-D-2556
L22-------------- Coil------------1-------------------- Band D, r. f., osc_1 SC-D-2556
TM 11—278
41
SIGNAL CORPS
104
a. Radio receiver BC-312—Continued.
Reference stock No. Name of part Description Function Drawing No.
L23--------------- Coil-------------------------------- _ Band E, r. f., osc____ SC-D- 2556
L24--------------- Coil--------------------------------- Band F, r. f., osc_ SC-D-2556
L26--_------------ Coils-------------------------------- Ignition suppressor__ SC-D-2571
L26--------------- Coils-------------------------------- Ignition suppressor_ SC-D-2571
L27--------------- Coils-------------------------------- Ignition suppressor_ SC-D-2571
L,„ I2Z9802/10 ICoils of transformer 1st detector_ SC-D-2564
28 [2Z9802/ll__ J C-202.
t [2Z9803/3—(Coils of transformer ________________ 1st i. f _ _ __ SC-D-2564
29 |2Z9803/4___ J C-203.
t [2Z9804/3—(Coils of transformer ____________ __ 2d i. f_ _ _ ___ SC-D-2564
30 " ]2Z9804/4___ j C-204.
L3i--------------- Coil---------------------------------- C. w. beat oscillator_ SC-D-2563
L32--------------- Coil--------------------------------- Filter, c. w. oscillator________ SC-D-2563
LMi ---- 2Z5893--- Neon lamp----------------------------- Antenna overload protection. _ SC-A-1801
LM2---- 2Z5927--- Lamp LM-27------ Pilot lamp___ ______ Dial light______________________ SC-D-2573
LM3----- 2Z5927--- Lamp LM-27------ Pilot lamp__________ Dial light________ SC-D-2573
Ri------ 3Z4564--- Resistor RS-164- Wire-wound, ipsul.; 500 ohms, Cathode bias, 1st r. f_ SC-D-970
1 w.
R2------ 3Z4569--- Resistor RS-169- Carbon, insul.; 60,000 ohms, Screen grid, 1st r. f_ SC-D-970
w.
R3------ 3Z4549--- Resistor RS-149- _ Carbon, insul.; 40,000 ohms, Screen grid, 1st r. f_ SC-D-970
w.
R4------ 3Z4572--- Resistor RS-172- Carbon, 100,000 ohms, % w__ A. v. c. filter, 1st r. f_ SC-D-970
R5------ 3Z4567--- Resistor RS-167- Carbon, 1,000 ohms, % w_ Plate filter, 1st r. f_ SC-D-970
Ra------ 3Z4573--- Resistor RS-173- Carbon, 2 megohms, % w__ Grid, 2d r. f_ ______________ SC-D-970
R?------ 3Z4564--- Resistor RS-164- Wire-wound,insul.; 500ohms, Cathode bias, 2d r. f_ SC-D-970
1 w. ' |
RADIO SETS .SCR—1 9 3—A, ETC.
TM 11-273
41
105
R8 3Z4569 Resistor RS-169 Carbon, insul.; 60,000 ohms, Screen grid, 2d r. f SC-D-970
% w.
R9_______ 3Z4549____ Resistor RS-149___ Carbon, insul.; 40,000 ohms, Screen grid, 2d r. f_ SC-D-970
% w. * .
Rio______ 3Z4572__ Resistor RS-172____ Carbon, 100,000 ohms, % w_ A. v. c. filter, 2d r. f- SC-D-970
Rn_______ 3Z4567____ Resistor RS-167___' Carbon, 1,000 ohms, % w_ Plate filter, 2d r. f--- SC-D-970
R12______ 3Z4573__ Resistor RS-173_____ Carbon, 2 megohms, % w___ Grid, 1st det____________ SC-D-970
R13______ 3Z4568__ Resistor RS-168_____ Carbon, 50,000 ohms, % w_ Suppressor bias, 1st det_____ SC-D-970
Rm_______ 3Z4566__ Resistor RS-166_____ Wire-wound,insul.;350ohms, Cathode bias, 1st det---- SC-D-970
1 w.
R15______ 3Z4540__ Resistor RS-140_____ Carbon, insul.; 30,000 ohms, Screen grid, 1st det__ SC-D-970
% w.
R16______ 3Z4572__ Resistor RS-172____ Carbon, 100,000 ohms, % w_ A. v. c. filter, 1st det_ SC-D-970
R17______ 2Z4525__ Resistor RS-125_____ Carbon, insul.; 1,000 ohms, Plate filter, 1st det___ SC-D-970
% w.
R18______ 3Z4572__ Resistor RS-172____ Carbon, 100,000 ohms, % w_ A. v. c. filter, 1st i. f_ SC-D-970
R19______ 3Z4564__ Resistor RS-164_____ Wire-wound, insul.; 500ohms, Cathode bias, 1st i. f____ SC—D-970
1 w.
R20______ 3Z4563__ Resistor RS-163_____ Carbon, insul.; 60,000 ohms, Screen grid, 1st i. f- SC-D-970
1 w.
R21______ 3Z4549__ Resistor RS-149_____ Carbon, insul.; 40,000 ohms, Screen grid, 1st i. f- SC-D-970
% w.
R22____ -- 3Z4525___ Resistor RS-125___ Carbon, insul.; 1,000 ohms, Plate filter, 1st i. f----- SC-D-970
% w.
R23______ 3Z4550__ Resistor RS-150_____ Carbon, insul.; 100,000 ohms, A. v. c. filter, 2d i. f- SC-D-970
% w.
R24______ 3Z4564__ Resistor RS-164_____ Wire-wound, insul.; 500 ohms, Cathode bias, 2d i. f- SC-D-970
’ 1 w.
R23______ 3Z4563__ Resistor RS-163_____ Carbon, insul.; 60,000 ohms, Screen grid, 2d i. f-- SC-D-970
1 w.
R26______ 3Z4549____ Resistor RS-149___ Carbon, insul.; 40,000 ohms, Screen grid, 2d i. f- . SC-D-970
% w. %
TJML 11-273
41
SIGNAL CORPS
106
9
a. Radio receiver BC-312—Continued
-Ref crcn cc
No. Stock No. Name of part Description Function Drawing No.
R27------ 3Z4525---- Resistor RS-125---- Carbon, insul.; 1,000 ohms, Plate filter, 2d i. f_ SC-D-970
% w.
R28------ 3Z4571---- Resistor RS-171 ___- Wire-wound, insul.; 750 ohms, Cathode bias, diode_ SC-D-970
1 w.
R29-----4- 3Z4562--- Resistor RS-162---- Carbon, insul.; 250,000 ohms, A. v. c. filter, diode_ SC-D-970
% w.
R30------ 3Z4561---- Resistor RS-161---- Carbon, 1 megohm, % w___ A. v. c. load__________ SC-D-970
R31------ 3Z4565---- Resistor RS-165---- Wire-wound, insul.; 1,000 Cathode bias, 2d audio__ SC-D-970
ohms, 1 w.
R32------ 3Z4562---- Resistor RS-162---- Carbon, insul.; 250,000 ohms, Grid, 1st a. f____ SC-D-970
% w.
R33------ 3Z4531---- Resistor RS-131--- Carbon, insul.; 50,000 ohms, Grid, 2d a. f_____ SC-D-970
% w.
R35______j'2Z7289--- Potentiometer RS-174. oyimsSj’1 w------- Dual volume control_______ SC-D-1982
R36------ 3Z4550---- Resistor RS-150---- Carbon, insul.; 100,000 ohms, Minimum bias bleeder_ SC-D-970
% w.
R37------ 3Z4550---- Resistor RS-150---- Carbon, insul.; 100,000 ohms, C. w. osc. plate___ SC-D-970
% w.
Rss------ 3Z4578---- Resistor RS-178----- Metal encased; 15 w., 12ohms, Heater_______________
14 v.
Rss------ 3Z4578---- Resistor RS-178---- Metal encased, 15 w., 12 ohms, Heater_
14 v.
R40------ 3Z4578---- Resistor RS-178---- Metal encased; 15 w., 12 ohms, Heater_f._____________
14 v.
R«------- 3Z4539---- Resistor RS-139---- Carbon, insul.; 30,000 ohms, 1 Plate, r. f. osc__ SC-D-970
w.
107
TM 11-273
RADIO SETS SCR—193—A, ETC. 41
♦
R42 3Z4540 Resistor RS-140 Carbon, insul.; 30,000 ohms, Grid, r. f. osc----------------------- SC-D-970
w.
R43______ 3Z4548___ Resistor RS-148___ Carbon, insul.; 200,000 ohms, Grid, c. w. osc---------- SC-D-970
V2 W.
R44______ 3Z4527___ Resistor RS-127___ Carbon, insul.; 3,000 ohms, Cathode, band C, r. f. osc- SC-D-970
y w.
R45______ 3Z4528____ Resistor RS-128____ Carbon, insul.; 5,000 ohms, Cathode, band B, r. f. osc- SC-D-970
y w.
R46______ 3Z4577____ Resistor RS-177_ Carbon, insul.; 7,500 ohms, Cathode, band A, r. f., osc- SC-D-970
y w.
R47______ 3Z4576___ Resistor RS-176 ___ Carbon, insul.; 60 ohms, ^ w__ Filament shunt, diode- SC-D-970
R48______ 3Z4569____ Resistor RS-169__ Carbon, insul.; 60,000 ohms, Screen grid, 1st det- SC-D-970
• y w.
R49______ 3Z4533___ Resistor RS-133___ Carbon, insul.; 500,000 ohms, R. f. filter, diode- SC-D-970
% w.
R50______ 3Z4540..__ Resistor RS-140__ Carbon, insul.; 30,000 ohms, Screen grid, 1st det----- SC-D-970
y w.
R81______ 3Z4529___ Resistor RS-129___ Carbon, insul.; 10,000 ohms, Filter load, c. w. osc-- SC-D-970
i w.
R52______ 3Z4575___ Resistor RS-175__ Carbon, 10,000 ohms, % w___*_ A. v. c. filter, 1st i. f- SC-D-970
R53______ 3Z4573___ Resistor RS-173__ Carbon, 2 megohms, % w-- Grid, 1st r. f----------------- SC-D-970
RLj______ 2Z7613____ Relay BK-13___________________________1__. Antenna grounding--------------- SC-D-1942
SOi______ 2Z8794.1__Socket SO-94______________________________ Power supply and control----------SC-D-2592
SWi______ 3Z8131____ Switch SW-131____ Toggle_______-_________ Send-receive----------------- SC-A-1042
SW2______ 3Z8310-2 (Band change, 1st r. f. grid- SC-D-2553
SW3______ 3Z8310-1__ . Band change, 1st r. f. antenna. SC-D-2553
SW<____+ ___ 3Z8310-2... Band change, 2d r. f. grid---------- SC- D-2553
SW5______ 3Z8310-2___ Switch__________ Ganged_________________< Band change, 1st r. f. plate-__ SC-D-2553
SW6______ 3Z8310-2___ * * < Band change, 1st det. grid------ SC-D-2553
SW,______ 3Z8310-2—- Band change, 2d r. f. plate_SC-D-2553
SW8______ 3Z8310-2__ Band change, r. f. osc. grid-SC-D-2553
SW9______ 3Z8310-2___ (Band change, r. f. osc. plate._ SC-D-2553
TM 11-273
41
SIGNAL CORPS
108
a. Radio receiver BC-312—Continued.
crcn co
No. Stock No. Name of part Description Function Drawing No.
SWio-------------- Switch----------- Ganged to C51-------- Crystal switch______ SC-D-2564
SWn----- 3Z8105--- Switch SW-105---- Toggle-----------.--- G. w. beat osc_______ SC-A-1042
SW12---- 3Z8119--- Switch SW-119---- Rotary--------------- Off MVC AVC ___ SC-D-2574
SW13---- 3Z8131--- Switch SW-131---- Toggle--------------- Heater switch______ SC-A-1042
T1----- 2Z9805---- Transformer C-205- Audio frequency 5,000/2,500 1st audio___ SC-D-2567
turn ratio.
T2----- 2Z9760---- Transformer C-160- Audio frequency 5,000/1,885 2d audio____ SC-D-2569
turn ratio.
THSi---- 2Z9182--- Temperature control '2.3 a., 14 v., normally closed__ Opens at 111° F _ SC-A-2590
BK-12.
THS2---- 2Z9181--- Temperature control 1.15 a., 14 v., normally closed . Opens at 109° F _ _ _ SC—A—2590
BK-11.
TM 11-273
41
RADIO SETS SCR—193—A, ETC.
b. Radio receiver BC-312-C.—Replaceable parts of the radio receiver BC-312-C are identical with those parts listed in a above for the receiver BC-312 except as noted in (1), (2), and (3) below.
(1) Additions.—The following item is added in parallel with R31; R54; 3Z4623; resistor RS-223; wire-wound, insulated; 2,000 ohms, 1 watt; cathode bias, 2d audio.
(2) Deletions.—The following items are not used: capacitors C77, C39, C90, C91, C92, C93; resistors R39, R4q; switch SAV43; and thermostats THSi, THS2. Resistor R38, the heater resistor of the BC-312, is not used as such. The resistor designated as R38 in the BC-312-C is actually a plate loading resistor in the 1st i. f. stage.
109
TM 11-273
41
SIGNAL CORPS
110
(3) Changes.
Reference c, , XT AT *
No. btock No. Name of part Description Function Drawing No.
C52----- 3D342--- Capacitor CA-342-- Mica; 100 -------- 1st i. f. grid coupling________ SC-D—1993
C53----- 3D344--- Capacitor CA-344-- Mica; 400 urf_____ 1st det. plate__ SC-D-1993
C54----- 3D371--- Capacitor CA—371-- Mica; 0.01 ,uf.-450 v_ 1st det. plate bypass_ RL—D—6222
C55----- 3D344--- Capacitor CA-344__ Mica; 400 M/zf________ 2d i. f. grid_____ SC-D-1993
C56----- 3D371--- Capacitor CA-371-- Mica; 0.01 A -450 v___ 2d i. f., a. v. c. bypass_ RL-D-6222
C57----- 3D344--- Capacitor CA-344-- Mica; 400 juMf_______ 1st i. f. plate_ SC-D-1993
C58----- 3D371--- Capacitor CA-371-- Mica; 0.01 pf-450 v___ 1st i. f. plate bypass_ RD-D-6222
C63----- 3D371--- Capacitor CA-371-- Mica; 0.01 pf.-450 v__ 1st i. f., a. v. c. bypass_ RL-D-6222
Cbi----- 3D342--- Capacitor CA—342-- Mica; 100 /z/zf_______ Diode input________________ SC—D—1993
Cbs----- 3D342--- Capacitor CA-342._ Mica; 100 uA______ 2d i. f. plate__ SC-D-1993
Cbs----- 3D371--- Capacitor CA—371-- Mica; 0.01 /zf.—450 v_ Diode a. v. c. coupling_ RL-D—6222
C76----- 3D371--- Capacitor CA-371-- Mica; 0.01 4--450 v___ 2d audio coupling_ RL-D-6222
C84----- 3D280--- Capacitor CA—280-- Variable air, with shaft; C. w. osc. tuning____ SC—A—1728
1-10 MMf-
CX---•— 3Z3501-6A _ Crystal DC-6-A-- 470 kc---------------- Crystal filter unit_ SC—D-2972
DM------ 3H1621-B.. Dynamotor DM-21-B------------------ D. c. power pack___ SC-A-2581
FL------ 3Z1890-6B _ Filter FL-6-B--------------------- D. c. power pack________ SC-D-1866
Fi------ 3Z1921A- Fuse FU-21-A------ 10 a.-25 v-------- Dynamotor and filaments_____
F2------ 3Z1921A-Fuse FU—21—A------- 10 a.—25 v________ Lamp circuit______
Ji------ 2Z5534A-Jack JK—34r-A----------------------------- 1st audio phones________
J2------ 2Z5534A-- Jack JK-34-A---------------------------- 2d audio phones_________
J3------ 2Z5533A--Jack JK—33—A------------------------- Speaker jack____________
J4------1 2Z5533A-Jack JK—33—A------------------------- Microphone jack_____________
TM 11-273
RADIO SETS SCR—19 3—A, ETC.
41
111
JB_______ 2Z5534A__Jack JK-34-A_________ ... --- ------ ---- Key jack-----------------------
L28________________ Coils of transformer C-282_____________•. 1st detector------SC-D-2564
L29__________?____ Coils of transformer C-283_______________ 1st i. f------------- SC-D-2564
L30______________ Coils of transformer C-284_______________ 2d i. f----------’---- SC-D-2564
R38_____ 3Z4569___ Resistor RS-169_ 60,000 ohms, % w_______ 1st i. f. plate circuit loading. SC-D-970
c. Radio transmitters BC-191—A and BC-191-C.
Reference Stock No. Name of part Description Function
_________ 2C6191A_______ Radio transmitter BC- 75 w_________________
191-A.
______________________ Radio transmitter BC- 75 w_________________
191-C.
1101_____ 2C6191A/S2____ Socket____________ For VT-4-C______________ For m. o. tube.
1102_____ 3Z9622________ Switch, interlock_ Pushbutton, nonlocking-- High-voltage protection.
1103____________________ Capacitor_________ Thermal compensator_____ Thermal compensation of m. o.
tank.
1104____________________ Capacitor_________ Part of 1103____________ Calibration reset.
1105_____ 3DA6-4________ Capacitor_________ 0.006 A- ± 10 percent, 2,500 v_ _ M. o. plate bypass.
1106___ _ 2C6191A/D1____ Choke_____________ Fixed r. f______________ M. o. plate.
1107_____ 3DA20-6_______ Capacitor_________ 0.02 A- ± 10 percent, 1,000 v___ Filament bypass.
1108_____ 3D9100-12_____ Capacitor_________ 0.0001 juf. ± 10 percent, 1,000 v_ M. o. grid bypass.
1109_____ 3Z6250________ Resistor__________ 2,500 ohms ±5 percent, 15 w__. M. o. grid bias.
1110____t 2C6191A/S2____ Socket____________ For VT-4-C-------------- For p. a. tube.
1111_____ 3D9100-12_____ Capacitor_________ 0.0001 A- ± 10 percent, 1,000 v_ P. a. grid bypass.
1112_____ 3Z6400-1______ Resistor__________ 4,000 ohms ±5 percent, 15 w— Part of p. a. grid bias.
• <
TM 11-273
41
SIGNAL CORPS
c. Radio transmitters BC-191-A and BC-191-C—Continued.
TLcf crcn cc
No. Stock No. Name of part Description Function
1113--- 2C6191A/R31----- Resistor----------- 3,000 ohms ±5 percent, no taper, Mod. bias control.
variable part of p. a. bias.
1114----- 2C6191A/R31. Resistor----------- 3,000 ohms ± 5 percent, no taper, S. a. bias control.
variable part of p. a. grid bias.
1115----- 3Z6720------- Resistor------------ 200,000 ohms ± 10 percent, 1 w_ Part of keying circuit.
1116----- 3Z6725__------ Resistor----------- 250,000 ohms ± 10 percent, 1 w_ High voltage bridge.
1117----- 3DA1—9-------- Capacitor---------- 0.001 /xf. ±5 percent, 4,500 v_ P. a. plate power bypass.
1118-------------------- Choke coil--------- Fixed r. f_____________________ P. a. plate.
1119----- 2C6191A/D2---- Choke coil--------- Fixed r. f___------------------ Negative high-voltage return.
H20------ 2C6191A/C5---- Capacitor--------- 1 pf.—1,200 v., d. c------------ R. f. bypass high-voltage supply.
1121----- 3F222.1------- Ammeter IS-22------ 500 ma., d. c., blocked in red TOTAL PLATE CURRENT
from 210 to 220 ma. meter.
1122----- 3Z5927----- Lamp LM—27------------ 6.3 v., 0.25 a___________ Pilot lamp.
H23------ 3Z6003—3------ Resistor----------- 30 ohms ±10 percent, 5 w_Series with 6.3 v. lamp.
1124----- 3Z6003-3------ Resistor----------- 30 ohms ±10 percent, 5 w- Series with pilot lamp in control
box BC-309.
1125---- 2Z8754-------- Socket SO-54-------- Alternate connection 1173 for Cording.
plug PL-74.
1126----- 2Z8741------ Socket SO-41--------- Alternate connection 1174 for Cording.
plug PL-61.
1127----- 2Z8739-------- Socket SO-39------- Alternate connection 1175 for Cording.
plug PL-59.
1128----- 2Z8744-------- Socket SO-44------- Alternate connection 1176 for Cording.
plug PL-64.
H29------ 2Z5533A------- Jack JK-33-A-----------------------.________I Microphone.
112
1130______ 2Z5534A________I Jack JK-34-A_____________________________'-------- Key.
1131______ 3Z9622_________ Switch______________ Pushbutton, nonlocking-------- Test key.
1132______ 3Z9623_________ Switch OFF ON_______ 2 position, rotation___________ Filament and dynamotor circuits.
1133______ 3F7322_________ Voltmeter IS-122____ 15 v. a. c., d. c., red line at 10 v__ Filament voltages.
1134______ 3DA10-17_______ Capacitor___________ 0.01 rf. ±10 percent, 1,000 v- R. f. bypass on voltmeter.
1135______ 3Z8106_________ Switch SW-106_______ Single pole double throw, 1 a, C. w. filament or mod filament
250 v.; 3 a, 125 v. voltage.
1136______ 3Z9624_________ Switch AC DC________ Ganged with 1137_______________ A. c. or d. c. operation of fila-
• ments. .
1137______ 3Z9624_________ Switch AC DC________ Ganged with 1136_______________ A. c. or d. c. operation of fila-
ments.
1138______ 2C6191A/R5_____ Resistor_____________ 1.2 ohms blue stick resistor Filament voltage adjustment.
mounted to tapped connec-
tion board.
1139______ 3Z9624_________ Switch 12v 14.2v_____ Ganged to 1140---------------- For 12 v. or 14.2 v. battery
voltage.
1140______ 3Z9624_________ Switch 12v 14.2v_____ Ganged to 1139----------- For 12 v. or 14.2 v. battery
• voltage.
1141______ 3Z9625_________ Switch selector TONE 3 position_______________ Select tone c. w. or voice opera-
CW VOICE. tion.
1142______ 3DA1-10________ Capacitor____________ 0.001 A- ± 10 percent, 2,500 v_ _ Oscillator feed back on tone or c.w.
1144______ 3DB1.1A________ Capacitor____________ 1 /if. ±10 percent, 300 v- S. a. grid bypass.
1145______ 3Z6005-2_______ Resistor_____________ 50 ohms ± 10 percent, 5 w- Microphone circuit.
1146______ 2C6191A/K1_____ Reactor______________ Iron cored-------- Microphone filter item.
1147______ 2C6191A/C9_____ Capacitor____________ 25 pi. plus 40 percent minus 10 Microphone filter item.
percent, 25 v.
1148______ 2C6191A/R32____ Resistor_____________ 200 ohms ± 10 percent, variable S. a. input level control.
no taper.
1149______ 2C6191A/T3_____ Transformer_________ Microphone---------------- Input to s. a.
1150___3DA1-7_____________ Capacitor____________ 0.001/if. ±5 percent, 2,500 v- Resonating capacity on tone or
c. w. operation.
1151______ 3Z6020-4_______ Resistor_____________I 200 ohms ± 5 percent, 3 w- Grid bias stabilization.
296642°—41
-8
113
TM 11-273
RADIO SETS ,SCR—19 3—A, ETC. 41
TM 11-273
41
SIGNAL CORPS
114
c. Radio transmitters BC-191-A and BC-191 -C— Continued.
No. Stock No. Name of part Description Function
1152----- 3Z5991-2----- Resistor---------- 1 ohm ± 5 percent, 5 w_________ Filament s. a. tube.
1153----- 3Z5991-2----- Resistor---------- 1 ohm ± 5 percent, 5 w_ Filament s. a. tube.
1154----- 2Z8759------- Socket------------ For VT-25_____________ For s. a. tube.
1155----- 2C6191A/C5--- Capacitor--------- 1 4.-1,200 v. d. c____ S. a. plate bypass.
1156----- 3Z6611-1----- Resistor---------- 11,000 ohms ± 5 percent, 15 w___ S. a. plate, voltage reducing.
1157----- 2C6191A/T2--- Transformer------- Interstage____________ S. a. to mod. grids.
1160----- 3DB1.1A------ Capacitor--------- 1 4- ± 10 percent, 300 v. d. c_ Mod. grid bypass
1161----- 2C6191A/S2-- Socket------------- For VT-4-A____________ Modulator tube.'
1162----- 2C6191A/S2---- Socket----------- For VT-4-A____________ Modulator tube.
1163________ 2C6191A/C5- Capacitor-------- 1 4.-1,200 v. d. c____ Mod. plate power bypass.
1164----- 2C6191A/T1--- Transformer------- Modulation____________ Mod. tubes to p. a.
1165----- 2C6191A/L1--- Relay------------- Antenna switching----- Antenna switching and trans-
mitter keying.
1166----- 3F289-------- Ammeter IS-89----- 8 a., r. f., with internal thermo-
couple.
1167------------------- Inductor---------- Rotating continuously variable, _ ANT IND TUNING.
1168----- 3Z9626------- Switch------------ 4 position_____________ ANT CIRCUIT SWITCH.
1169------------------- Capacitor--------- 22 to 118 m4__________ Antenna tuning.
1170------------------- Inductor---------- Tapped inductor---------------- Antenna loading.
1171----- 3Z9627------- Switch------------ 5 position_____________________ ANT IND SWITCH
1172----- 3Z1912------- Fuse FU-12-------- .5 a., 1,000 v,r_____High-voltage supply. ’
1173----- 2Z8754------- Socket SO-54------ For plug PL-74________ Cording.
1174----- 2Z8741------- Socket SO-41------ For plug PL-61________ Cording.
11^5----- 2Z8739------- Socket SO-39------ For plug PL-59_________________ Cording.
1176---- 2Z8744-------- Socket SO-44------ For plug PL-64________ Cording.
1177,---- 2Z5533A------ Jack JK-33-A------------------------------ Microphone.
TM 11-273
41
RADIO SETS SCR—19 3—A, ETC.
1178_____ 2Z5534A______ Jack JK-34-A_______________________________________ Key.
1179_____ 3Z9610A______ Switch____________ Single section, one circuit, four SIDE TONE adjustment.
point, nonshorting.
1180_____ 3DA10-13_____ Capacitor_________ 0.01/zf. ±5 percent, 2,500 v_ Plate resonating capacitor, tone,
and c. w.
1181_____ 3Z6630-4_____ Resistor__________ 30,000 ohms ± 5 percent, 1 w---- Mod. grid stabilization.
1182_____ 3Z6005-2_____ Resistor__________ 50 ohms ± 10 percent, 5 w_______ Microphone circuit.
1183_____ 3Z6010-6_____ Resistor___r______ Parallel with 1184______ Parasitic resistor.
1184___________________ Choke____________R. f. parallel with 1183__ Parasitic choke.
1185_____ 3DB1.1A______ Capacitor_________ 1 gf. ± 10 percent, 300 v. d. c- Keying filter.
1186_____ 3Z5995_______ Resistor__________ 5 ohms ± 5 percent, 3 w- Keying filter.
I _________ »_____________________'_______________.____
d. Transmitter tuning unit TU-5-A.
Reference Stock No Name of part Description Function
_________ 2C8005A______ Transmitter tuning unit ---------------------------
TU-5-A.
501____________________ Inductor__________ R. f. fixed____________ M. o. tank.
502______ 3Z9614_______ Switch____________ Ganged with 522, 4 position----- BAND CHANGE SWITCH.
503______ 3D9100-11____ Capacitor_________ 0.0001 pf. ±5 percent, 3,000 v_ _ M. o. tank, band change.
504______ 3D9100-11____ Capacitor_________ 0.0001 A- ±5 percent, 3,000 v__ M. o. tank, band change.
505______ 3D9100-11____ Capacitor_________ 0.0001 gf. ±5 percent, 3,000 v__ M. o. tank, band change.
506______ 3D9030-l_____ Capacitor_________ 0.00003 Mf- ±5 percent, 2,000 v_ M. o. tank.
507____________________ Capacitor__________ 135 g/zf- max. ±2 percent, 20 M. o. tank, variable.
ggf. min. ± 1 percent.
508______ 2C8005A/D10__ Choke_____________ With resistor 517______ P. a. grid circuit.
509______ 3D9400-6_____ Capacitor_________ 0.0004 fit. ± 10 percent, 5,000 v_ P. a. grid blocking.
510______ 3D9400-6____ Capacitor__________ *0.0004 Mf. ± 10 percent, 5,000 v_ P. a. grid blocking.
115
TH 11-273
41
SIGNAL CORPS
116
d. Transmitter tuning unit TU-5-A—Continued.
R/ef cron ce
No. Stock No. Name of part Description Function
511------ 2C8005A/D11--- Choke------— R. f. fixed_____________ M. o. grid.
512-------------------__ Capacitor--------__ 8 to 26 nA-------------------- Neutralizing.
513------------------- Capacitor------------ Parallel to 503--------- Thermal compensator.
514--------------------- Capacitor---------- Parallel to 504_________ Thermal compensator.
515-------------------Capacitor------------- Parallel to 505_________ Thermal compensator.
516--------------- ----- Capacitor---------- Parallel to 506--------- Thermal compensator.
517------ 3Z6001E5------ Resistor----------- 15 ohms, 4.5 w., with 508_ P. a. grid parasitic.
521--------------------- Inductor----------- R. f. fixed_____________ P. a. tank.
522------ 3Z9614___<_--- Switch------------- With 502, 4 position____ BAND CHANGE SWITCH.
523------ 3D9090-------- Capacitor--------- 0.00009 A- ±5 percent, 3,000 v__ P. a. tank, band change.
524------ 3D9090-------- Capacitor---------- 0.00009 A- i 5 percent, 3,000 v__ P. a. tank, band change.
525_----- 3D9090------ _ Capacitor---------- 0.00009 A- ±5 percent, 3,000 v__ P. a. tank, band change.
527------------------- Capacitor----------- 20 to 156 nA--------------- P. a. tank, variable.
528------------------ Inductor------------ Tapped-------------------- Antenna coupling.
529------ 3Z9605A----- Switch--------------- 6 position______________ ANT COUPLING SWITCH.
TM 11-273
RADIO SETS SCR—19 3—A, ETC. 41
Transmitter tuning unit TU-6-A.
Reference Stock No. Name of part ■ Description Function
_________I------------------------------------------------------_________ 2C8006A______ Transmitter tuning unit ---------------.________________________
TU-6-A.
601____________________ Inductor__________ R. f. fixed------------ M. o. tank.
602______ 3Z9612A______ Switch____________ 2 position, ganged with 622- M. o. tank, band change.
603______ 3D9050-3_____ Capacitor_________ 0.00005 4- ±5 percent, 3,000 v__ M. o. tank, band change.
607____________________ Capacitor_________ 77/z4- ±2 percent max., 15 nA- M. o. tank.
± 1 percent min. variable.
608______ 3C8006A/D14__ Choke_____________ With resistor 614------ P. a. grid.
609______ 3D9400-6_____ Capacitor_________ 0.0004 4- ± 10 percent, 5,000 v_ P. a. grid blocking.
610______ 3D9400-6_____ Capacitor_________ 0.0004 4. ±10 percent, 5,000 v_ M. o. grid blocking.
611______ 2C8006A/D15__ Choke_____________ R. f. fixed------------ M. o. grid.
612____________________ Capacitor_________ 8 to 26 nA______-______ Neutralizing.
613____________________ Capacitor_________ Parrallel to 603_______ Thermal compensation.
614______ 3Z6001E5_____ Resistor__________ 15 ohms, 4.5 w------------- Parasitic p. a. grid.
621____________________ Inductor__________ R. f. fixed---------------- P- a. tank.
622______ 3Z9612A______ Switch____________ 2 position ganged with 602- P. a. tank, band change.
623______ 3D9050-1_____ Capacitor_________ 0.00005 4- ±5 percent, 3,000 v. P. a. tank, band change.
627____________________ Capacitor_________ 19 to 116 nA- variable- P. a. tank.
628____________________ Inductor__________ Tapped_____________________ Antenna coupling.
629______ 3Z9605A______ Switch____________ 6 position----------------- ANT COUPLING SWITCH.
117
TH 11-273
41
SIGNAL
CORPS
f. Radio control box BC-309.
Reference Stock No Name of part Description Function
1301---- 2Z8754------- Socket SO-54------ For plug PL-74________ Cording.
iJnQ---- a’------ Switch----------- Toggle---------------- Transmitter OFF ON.
1303---- 2Z5534A______ Jack JK-34-A___________________________ Kev
1304---- 3Z5927------- Lamp LM-27-------- 6.3 v., 0.25 a________ Pilot lamp.
g. Dynamotor unit BD-77-A.
lief cron cc
No. Stock No. Name of part Description Function
1601---- 2Z8741------ Socket SO-41------- For plug PL-61________ Cording.
1602---- 2Z8739------- Socket SO-39------ For plug PL-59________ Cording.
1603___---------------- Relay----------------------------------- Starting.
----- 3Z1913------- FuseFU-13-------- 30 a., 250 v-1_________ To transmitter.
605----- 3Z1922------- Fuse FU-22------- 60 a., 250 v__________ To dynamotor.
Z------- 3H1777AA----- Dynamotor--------- 14/100 v., 5,000 r. p. m_ High-voltage supply.
' Capacitor-------- .005 /4- ±5 percent, 5,000 v- High-voltage filter, bypass,
icon Fuse FU-18-A------ 1 a., 1,000 v--------- High-voltage supply.
1609---- 3DA10-17----- Capacitor--------- .01 Mf„ 1,000 v-■_____ Low-voltage filter, bypass.
'----------------------------------------------------------------I_________
118
RADIO SETS SCR—19 3—A, ETC.
TM 11-273
41
119
h. Mountings.
Reference Stock No. Name of part Description Function
No. ' .
_ _____3H3907________Mounting FT-107_________________________ For use with dynamotor unit
BD-77-A.
________ 2Z6665B____ Mounting FT-115-B----------------------- Disposable for use with radio transmitter BC—191-A.
3Z6691A____ Mounting FT-151-A________________________ For use with radio transmitter
BC-191-A.
[A. G. 062.11 (1-10-41).]
TM 11-273
41
SIGNAL CORPS
By order of the Secretary of War:
G. C. MARSHALL,
Chief of Staff. Official:
E. S. ADAMS,
Major General,
The Adjutant General.
Distribution:
B (3); R 2, 6 (10); IBn 2, 6 (3); C 11 (2); IC 2, 6, 11 (5).
o
120
NTSU LIBK/w
UNT LIBRARIES DENTON TX 78203
lllllllllllllll
1001895981