[Oscilloscope I-245-A]
[From the U.S. Government Publishing Office, www.gpo.gov]
101. />\\ / I
y vertical.
D* REST POSITION
) iln.\ ) ^\. Operator releases pressure ——■
” Al \ Jv 'v suddenly, swings back on f \
Cr-A heels, and rests for 2 ( yA.
W/27 fri—* seconds.
B 0 D
seconds for a complete cycle. Until the operator is thoroughly familiar with the correct cadence of the cycle, he should count the seconds aloud, speaking distinctly and counting evenly in thousands. Example: one thousand and one, one thousand and two, etc.
h- Artificial respiration should be continued until the victim regains normal breathing or is pronounced dead by a medical officer. Since it may be necessary to continue resuscitation for several hours, relief operators should be used if available.
matic spirits of ammonia, the individual administering the stimulant should first test.it himself to see how close he can hold the inhalant to his own nostril for comfortable breathing. Be sure that the inhalant is not held any closer to the victim’s nostrils, and then for only 1 or 2 seconds every minute.
b. After the victim has regained consciousness, he may be given hot coffee, hot tea, or a glass of water containing % teaspoon of aromatic spirits of ammonia. Do not give any liquids to an unconscious victim.
CAUTIONS.
RELIEVING OPERATOR.
The relief operator kneels beside the operator and follows him through several complete cycles. When the relief operator is sure he has the correct rhythm, he places his hands on the operator’s hands without applying pressure. This indicates that he is ready to take over. On the backward swing, the operator moves and the relief operator takes his position. The relieved operator follows through several complete cycles to be sure that the new operator has the correct rhythm. He remains alert to take over instantly if the new operator falters or hesitates on the cycle.
STIMULANTS.
a- If an inhalant stimulant is used, such as aro-
a- After the victim revives, keep him LYING QUIETLY. Any injury a person may have received may cause a condition of shock. Shock is present if the victim is pale and has a cold sweat, his pulse is weak and rapid, and his breathing is short and gasping.
b. Keep the victim lying flat on his back, with his head lower than the rest of his body and his hips elevated. Be sure that there is no tight clothing to restrict the free circulation of blood or hinder natural breathing. Keep him warm and quiet.
c- A resuscitated victim must be watched carefully as he may suddenly stop breathing. Never leave a resuscitated person alone until it is CERTAIN that he is fully conscious and breathing normally.
Til 5338 F
835265—49----2
IX
TM 2689A-I
Figure 1. Oscilloscope
X
CHAPTER 1
INTRODUCTION
Section I. DESCRIPTION
1. Purpose and Use
Oscilloscope 1-245-A (fig. 1) is a general purpose test oscilloscope used for viewing waveforms and for checking frequencies and phase relations at various test points in radio and radar sets. The instrument incorporates a cathode-ray tube using electrostatic focusing and deflection and connected in a conventional cathode-ray oscilloscope circuit. A linear sweep, or timebase, is generated internally. The amplitude and frequency of this sweep is variable. Different types of synchronizing signals with varying amplitudes may be applied. The signal to be viewed is applied to the vertical deflecting plates through an amplifier with variable gain. For special purposes external signals may be applied to the horizontal deflecting plates through the X-axis amplifier, or to either pair of deflecting plates directly.
2. Technical Characteristics
Cathode-ray tube:
Type-----------5CP1, high vacuum, in-
tensifier.
Diameter_______5 inches.
Deflection_____Electrostatic.
Focusing_______Electrostatic.
Persistence____Medium.
Accelerating 1,400 volts, potential.
Input impedance:
Y-axis ampli- 2 meg (megohms), 42 fier. mmf (micromicrofar-
ads) maximum.
X-axis ampli- 5 meg, 34 mmf maximum, fier.
Maximum input potential:
Y-axis ampli- 250 volts, rms (root mean fier. square).
X-axis ampli- 25 volts, rms. fier.
Amplifier frequency response:
Y-axis-------- ±10 percent of maximum
from 2 to 100,000 sinusoidal cps (cycles per second). 50 percent
response at 325,000 sinusoidal cps.
X-axis-------- ±10 percent of maximum
from 2 to 100,000 sinusoidal cps. 50 percent response at 250,-000 sinusoidal cps.
Voltage gain:
Y-axis-------- 2,000 times ±10 percent.
X-axis________35 times.
Deflection factor:
Through amplifier:
Y-axis— 0.007 rms volts per inch.
X-axis— 0.4 rms volts per inch.
To deflection plates:
Y-axis— 40 d-c (direct-current) volts per inch.
X-axis— 37 d-c volts per inch.
Sweep circuit:
Sweep direc- Left to right, tion.
Frequency 2 to 50,000 cps. (recurrent only).
Tubes and functions:
1—5CP1 cathode-ray tube.
3—6SN7GT or 6SN7 amplifiers.
4—6V6GT impedance matching and positioning tubes.
1—6V6GT regulator tube.
1—6X5GT rectifier.
1—5Y3GT rectifier.
1—5R4GY rectifier.
1—6SJ7 regulating amplifier.
1—884 gas discharge tube.
1—VR105-30 regulator tube.
, ® f , K -
v -^aasifc.. z
V VMHHhL *
7 . ? :^HSBI». <
I I ■!■ Y I
Ymh I
A T/u
4 B
■ 4-^"—'=Z VS""’* ■■ ■-'"f\''" ~~~f )
-n y q 5 C I
40 3.° 60 40 30 60
HH r-rosiTioM so \ I JL zo so \ I L zo x-fosition
•RAM OM 20— £/ZZC-80 ’0- 80 rowct oh
|Sl 10^J*Z#^90 IO-^xX/^S’O /fgfe
’<2Z o too o ioo xC#^
INTENSITY FOCUS
HH <-«>■*« t«»z ■HhKJ
I I
40 SO 40 40 ,3°t**2K 40 30 SO**- KJ
JF 1 \ 3< \ 1 X 7° a \ J / j ax 3K \ J z\7°
& 2 — 25K 2°—
’O"^*^"90 10^—s'»0
Z \>o ”’ M« Z \m
SYNC. SIGNAL FINE COARSE SYNC. SIGNAL
SELECTOR FREQUENCY FREQUENCY AMPLITUDE
f ?jH * ...A' *0 3.° 60 H*'**** 40 S.° 60
3 "v 3°xx Xz° A x dt ** * 3ox^ z
20-^Ra80 20-^^80 Iu.:»w,.,o.fHI
i°/Z ^'<>o ///f 10 7 90 *,ON*1 ,M,ur £
o ^ioc //// oz ^ioo
GAIN >/4aIN GAIN
VERNIER VERNIER
GSOUNO (flffw GXOUHO
tv Y-AXIS X-AXIS
AMPLIFIER AMPLIFIER '"a |f!z]
I Nl>.,w.x7 MADE IN '..A. A MWr-
Fir/ure 2. Oscilloscope 1-2^5-A, front panel.
2
Power input:
Potential____ 115/230 volts ac (alter-
nating current).
Frequency____40 to 60 cps.
Power con- 100 watts.
sumption.
Fuse protec- 1.5 amperes, tion.
3. Physical Description
The oscilloscope is mounted in a black steel cabinet supplied with a carrying handle (fig. 1). All of tire controls and the input connection terminals for both amplifiers and the synchronizing circuit are located on the front panel (fig. 2). Direct connection to the deflecting plates may be made by means of terminals at the back of the case (fig. 3).
Access to the inside of the instrument is obtained by removing two screws at the back of the case and sliding the chassis and panel forward out of the case. The line fuse and power cord are at the back of the cabinet. The screen of the cathoderay tube is visible above the controls through an opening in the front panel and is covered by a removable plastic scale. The over-all dimensions, excluding the carrying handle and feet, are: height 14% inches, width 8% inches, and depth 18% inches.
4. Packaging Data
For shipment, Oscilloscope I-245-A is crated in a wooden box approximately 19 inches high, 14 inches wide, and 30 inches long. The total shipping weight is approximately 125 pounds and
F8OI
h JUMPERS
BLANKING if WITCH S2O4
, X-AXIS
: AMPLIFIER OUTPUT
■. TERMINALS
X-DEFLECTION X2
PLATE TERMINALS XI
1GRID TERMINAL
TO CATHODE-RAY I TUBE
JUMPERS
GROUND TERMINAL
CHASSIS MOUNTING SCREWS
TM 2689A3
Figure 3. Oscilloscope rear vieiv.
Yl Y-OEFLECTION
Y2 PLATE TERMINALS*
Y-AXIS AMPLIFIER^
A-C LINE CORD
3
DESICCANT-------—
1
CORRUGATED !S"*~PLYW00D
LzzxZ?^ ^\~— feltpad
r%,fe
J fV|U : | J
I ,'i' S ■* PLYWOOD I
1 /\ I
CORRUGATED
FIBERBOARD PAD //
TM 2689A-32
Figure 4> Oscilloscope packaging.
4
the box occupies 4.6 cubic feet. The wooden case contains three fiberboard cartons. One carton (approximately 18 inches high, 13 inches wide, and 25 inches long and weighing approximately 75 pounds) contains the oscilloscope; the other two cartons (each weighing approximately 5 pounds) contain vacuum tubes and test leads, respectively. The tubes contained in one carton
include spare tubes as well as operating tubes over 4 inches long, since these latter must be removed from the oscilloscope prior to shipment. Figure 4 illustrates a typical method for packaging the oscilloscope in a fiberboard carton. For applicable packaging, packing and marking specifications refer to appendix I, paragraph 4.
Section II. INSTALLATION
5. Unpacking, Uncrating, and Checking
Be very careful when unpacking or handling the equipment because it may be damaged easily. To unpack the oscilloscope follow the steps outlined below.
a. Place the packing case in a convenient location where it can be opened easily.
1) . The instrument is packed in a wooden box which contains three sealed fiberboard cartons. Cut the steel straps which bind the box and, as a safety precaution, fold the sharp ends back.
c. Remove the nails with a nail puller and remove the top and one side of the packing case. Prying off the top or sides may result in damage to the equipment.
d. Lift out the fiberboard cartons. Cut the sealing tape around the edges of the cartons and lift out the primary cartons. Remove the moisturevapor-proof barriers and open the primary cartons. Carefully remove the desiccant and cushioning materials. Lift out the equipment, and dust
and wipe it clean of all dirt or foreign matter.
e. Thoroughly inspect all parts of the oscilloscope for possible damage during shipment.
f. Check the components against the master packing slip.
Caution: If the chassis has received moistureproofing and fungiproofing treatment, do not remove any of the protective coating.
6. Installation
The equipment is shipped with some of the tubes installed; check the tubes to see that each one is in the correct socket. Install those tubes which were removed before shipping. Make sure that all tube clamps are seated firmly against the tube bases.
7. Removal from Service
When the oscilloscope is not in use, always be sure that the switches are OFF. The test leads should be removed, coiled, and stored.
Section III. INITIAL ADJUSTMENTS
8. Line-Voltage Selector
Remove the chassis from the cabinet and check the line-voltage selector switch (S206, fig. 31) to see that the power transformer is connected for the proper line voltage (115 or 230 volts).
9. Cathode-Ray Tube Adjustment
a. Start the oscilloscope as explained in paragraph 11.
&. If the sweep line is not horizontal, rotate the cathode-ray tube until the sweep is horizontal. To do this, disconnect the power cord of the oscilloscope from the power source and remove the chassis from the case. Then loosen the shield clamp and the adjusting screws on the tube socket, and turn the tube base and socket.
5
CHAPTER 2
OPERATING INSTRUCTIONS
Section IV. PREOPERATIONAL PROCEDURES
10. Preparation for Use
Before using Oscilloscope I-245-A, carefully read the instructions covering its operation. The oscilloscope is a delicate electrical instrument and must be handled carefully. Pay particular attention to all cautions in this manual. They are inserted to guide the user and to protect the equipment. Before turning on the oscilloscope, set the controls as follows (fig. 2) :
a. POWER and BEAM switches in the OFF position.
b. X- and Y-POSITION controls at midscale.
c. INTENSITY control completely counterclockwise.
d. FOCUS control at midscale.
e. COARSE FREQUENCY control at any position except OFF.
/. SYNC SIGNAL SELECTOR at INTERNAL.
c/. SYNC SIGNAL AMPLITUDE control completely counterclockwise.
h. Attenuator switch (labeled Y-GAIN) to the 25-volt or the 250-volt position according to the amplitude of the Y-signal input.
?. X-GAIN control at midscale.
j. Y-GAIN control completely counterclockwise.
Note. If direct-deflection tests are to be made, only a through d above apply.
11. Starting the Oscilloscope
Caution: Do not leave the oscilloscope beam on indefinitely with no signals applied to either pair
of deflecting plates. The screen of the cathoderay tube will be burned by the intense spot formed by the electron beam if the spot is left in one position too long. When observations are not being made, turn the BEAM switch OFF. This removes the spot or trace from the screen but permits the instrument to remain warmed up.
a. Set up the oscilloscope in the position where it is to be used.
b. Plug the line cord on the rear of the oscilloscope into an a-c line of the proper voltage.
c. Turn the POWER switch ON (fig. 2).
d. With a suitable ground wire, interconnect the oscilloscope and all other equipment used.
e. Make the connections to the terminals of the instrument according to the test that is to be made (sec. V).
f. Turn the BEAM switch ON.
g. Adjust the INTENSITY and FOCUS controls until the line on the screen is sharp and well-defined.
Note. These two controls usually are interdependent so that whenever the INTENSITY control is adjusted to change the brightness of the picture, the FOCUS control must be readjusted as well. However, if the 5CP1 type cathode-ray tube has been replaced with a type 5CP1-A (the two types are interchangeable), this effect is much less pronounced because changing the setting of the INTENSITY control has no appreciable effect on the focusing anode voltage.
h. Adjust the Y-POSITION control until the sweep line is centered vertically on the screen.
i. Adjust the X-GAIN and X-POSITION controls until the sweep line is the same length as the diameter of the screen and is centered horizontally.
6
Section V. OPERATION
12. General
a. Y-Axis. Y-axis deflection may be accomplished by applying the signal to be observed to the Y-SIGNAL INPUT terminal or the Y-direct-deflection terminals (Y1 and Y2). The latter connection is especially valuable when observing pulses or square waves of sufficiently large amplitude to give suitable deflection.
(1) Y-signal input. Signal for Y-deflection within the frequency and voltage range of the Y-amplifier (par. 2) are normally connected between the Y-SIGNAL INPUT terminal and the GROUND terminal (fig. 2). The amplitude of deflection produced then depends upon the setting of the Y-attenuator and Y-GAIN controls, and these are adjusted until the desired deflection is produced.
(2) Direct deflection. Signals may be connected directly to the Y-deflection plates of the cathode-ray tube by using the Y-deflection plate terminals (Y1 and Y2) on the terminal board at the back of the instrument (fig. 3).. The jumper between the upper and lower terminal of each pair is disconnected, and the connections are made to the upper terminals. The upper terminals connect directly to the Y-deflection plates of the cathode-ray tube, while the lower terminals connect to the Y-amplifier. When the internal Y-amplifier is being used, the upper terminals are shorted (by means of the jumpers) to the terminals directly beneath, thus connecting the amplifier to the Y-deflection plates. Resistors R230 andR231 (fig. 32) connect the Y-position-ing circuits of the oscilloscope to the deflection plates of the cathode-ray tube when the shorting jumpers are removed. This permits the use of the Y-positioning circuits when the input is connected directly to the Y-deflection plates of the cathode-ray tube.
b. X-Axis. X-axis deflection may be accomplished by any of the following: the sweep generator or linear timebase within the oscilloscope; an external signal at the X-SIGNAL INPUT posts; or an external signal at the direct deflection
terminals. The use of the sweep generator is covered in (3) below.
(1) X-signal input. When the COARSE FREQUENCY control is set to its extreme counterclockwise or OFF position, the X-axis amplifier is connected between the X-SIGNAL INPUT terminal and the GROUND terminal (fig. 2). With an external source of deflection voltage connected between these terminals, the amplitude of horizontal deflection produced then depends upon the X-GAIN VERNIER control. This control is adjusted until the desired deflection is produced. The range of signal voltage and frequency which may be used to give X-axis deflection is given in paragraph 2. If these values are exceeded, the X-amplifier may be overloaded and the pattern distorted.
(2) Direct deflection. Signals may be connected directly to the X-deflection plates of the cathode-ray tube by using the X-deflection plate terminals (XI and X2) on the terminal board at the back of the instrument (fig. 3). Connections to the terminals are made as described for the Y1 and Y2 plates in a (2) above.
(3) Sweep generator. The sweep generator is connected to the X-axis amplifier when the COARSE FREQUENCY control is set in any position except OFF. It produces a horizontal deflection of the beam by applying a sawtooth voltage to the X-deflection plates through the X-ampli-fier. The resulting horizontal deflection consists of a uniform motion of the beam from left to right on the face of the tube, followed by a rapid return of the beam to its starting point. This is repeated at a rate depending upon the setting of the COARSE FREQUENCY and FINE FREQUENCY controls (fig. 2). When the sweep is used to provide a timebase, it is ordinarily adjusted by means of the frequency controls to the same frequency as that of the Y-axis signal, or a frequency which is some simple fraction of the signal frequency, such as one-half or
835265—49——3
7
one-third. This produces a stationary pattern on the screen.
c. Synchronization. To hold the pattern stationary on the screen, it is necessary to apply a small synchronizing signal to the sweep generator. This signal is usually of the same frequency as the signal being observed, but may be a multiple or submultiple of that frequency if external synchronization is being used. This is accomplished by means of the SYNC SIGNAL AMPLITUDE and SYNC SIGNAL SELECTOR controls and the EXTERNAL SYNC SIGNAL terminal (fig. 2).
(1) Sync signal selector. The SYNC SIGNAL SELECTOR switch determines the source of the signal used for synchronizing.
(«) In the EXTERNAL position the switch permits synchronizing the timebase oscillations with a signal connected between ground and the EXTERNAL SYNC SIGNAL input post. The amount of signal necessary is discussed in paragraph 33c.
(&) When the switch is turned to the LINE FREQ position, a synchronizing signal is supplied from the power line.
(c) When the selector is in the INTERNAL position, part of the signal voltage is taken from a suitable point in the Y-amplifier and used to synchronize the sweep.
(2) Sync signal amplitude control. This control varies the amplitude of the synchronizing signal used. Always use the minimum amount of synchronizing voltage which gives a good synchronization. Excess synchronizing voltage may introduce nonlinearity in the sweep.
(3) External sync signal input. When synchronization is desired from a signal other than the power line or that amplified by the Y-amplifier, that signal voltage is connected to the EXTERNAL SYNC SIGNAL terminal and the SYNC SIGNAL SELECTOR is set at EXTERNAL.
Caution: Excessive synchronizing voltage fed to this terminal may cause distortion as described in paragraph 33c (4). One volt
peak-to-peak should be the maximum external synchronizing signal used, though pulses of short duration might require somewhat greater amplitudes. If only large values of external synchronizing voltage are available, a suitable series resistor should be connected to the external synchronizing signal input terminal to reduce this voltage to the maximum value given above.
d. Test Leads.
(1) Avoid the use of a shielded test lead or twisted leads in taking waveforms, since both of these shunt a high capacitance across the circuit under test and are likely to cause distortion, especially if the waveform is of a high frequency or contains high-frequency components. The ground lead must be securely connected at all times.
(2) Keep the ungrounded test lead away from other circuits to avoid the possibility of picking up unwanted voltages.. The test lead should be brought away from the test point in such a way as to introduce a minimum amount of coupling to other stages.
(3) Leads to the scope must be kept short when observing waveforms in grid circuits where the grid capacitance is small. The input of the oscilloscope has high impedence, but it will cause loading on another high-impedence circuit and may distort the wave form. The smallest reaction on a waveform is introduced when measuring the voltage across the output (cathode) of a cathode follower or across low-impedence circuits in general.
(4) In measuring waveforms in high-impedance circuits, do not handle the hot test lead. If this precaution is not observed, the waveform will be distorted as a result of loading the circuit and picking up a 60-cycle voltage.
(5) A misleading indication may sometimes be obtained as the result of a signal voltage picked up by the test leads. For example, a plate-to-grid coupling capacitor may be open, yet a signal appears at the grid. This effect can be recognized by distortion of the waveform due to the loss of low-frequency components.
8
13. Observation of Waveforms
a. Y-Signal Input.
(1) Adj ust all controls and connect the signal as explained in paragraphs 11 and 12a (1);
(2) Adjust the attenuator switch and Y-GAIN VERNIER control until a convenient amplitude of vertical deflection is obtained on the screen.
(3) Adjust the COARSE FREQUENCY and FINE FREQUENCY controls until one or more cycles of the waveform under test are seen. It is advisable to have two or three cycles of the waveform on the screen, especially if the waveform being tested is of a relatively high frequency; then disregard the cycle at the right end of the sweep (par. 33. Direct Deflection.
(1) Adjust the beam, linear timebase, and X-axis amplifier controls as explained in paragraph 11. Connect the signal voltage to be observed to the Y1 and Y2 terminals at the rear of the oscilloscope as described in paragraph 12a (2).
(2) Connect a jumper from the signal source to the EXTERNAL SYNG SIGNAL terminal.
(3) Set the SYNC SIGNAL SELECTOR to EXTERNAL.
(4) Adjust the COARSE ’FREQUENCY and FINE FREQUENCY controls until several cycles of the waveform under test are seen.
(5) When the pattern has been adjusted as closely as possible with the FINE FREQUENCY control, advance the SYNC SIGNAL AMPLITUDE control just enough to hold the pattern stationary.
c. Waveforms with Special Timebase. For some special purposes it is desirable to view waveforms on a circular, spiral, exponential, or other nonlinear timebase, or on a linear timebase of higher frequency than that furnished by the internal timebase generator of the instrument. This timebase voltage may be applied through the X-
axis amplifier (par. 126 (1) above) or directly to the horizontal deflecting plates (par. 126 (2) above). In either case, however, the synchronizing circuit in the oscilloscope is inoperative.
d. Comparison of Waveforms. When reference waveforms are supplied with equipment, the actual waveform taken at a given point with the oscilloscope should be quite similar to the reference waveform, provided there is no fault in the equipment. Some differences in shape may occur for the following reasons, however, even though the circuit is normal:
(1) The test leads to the oscilloscope may not be placed in the same manner.
(2) A different oscilloscope may be used having values of input resistance and capaci tance which differ from those of Oscilloscope I-245-A.
(3) The various controls in the equipment may not be in the same positions as when the reference waveforms were taken,. Note the conditions specified in the reference waveforms.
(4) The same number of cycles may not be present.
(5) The vertical or horizontal amplitudes of the reference waveforms and the test patterns may not be proportional. This will produce apparent differences between the shapes of the two waveforms when there is no real difference.
(6) Whether or not a waveform is regarded as abnormal depends on the symptoms accompanying the fault which is being traced. If it is considered that the fault could be caused by a minor difference in waveform at the point under test, then this discrepancy should be considered significant. Otherwise time should not be spent in hunting down the cause for relatively minor differences between the shapes of the reference waveform and the test waveform.
14. A-c Voltage Measurement
a. Calibration of Oscilloscope. The deflection sensitivity of the oscilloscope when used to measure a-c voltages may be varied over wide limits by adjustment of the Y-GAIN control. Calibration consists of adjusting the Y-amplifier gain to give a known deflection sensitivity. The
9
deflection sensitivity desired depends on the amplitude of the voltage to be measured. For small voltages, the greater sensitivities (smaller number of volts per inch) will be used. The procedure for adjusting the sensitivity to the desired value is as follows:
(1) Obtain a source of sinusoidal a-c voltage for calibrating the Y-amplifier. With an accurate a-c voltmeter, measure the rms value of this voltage.
(2.) Multiply the rms value of the calibrating a-c voltage by 2.83 to obtain its peak-to-peak value.
Note. For greatest accuracy, the calibrating voltage selected should have a peak-to-peak value as close as possible to the expected peak-to-peak value of the voltage to be measured.
(3) Multiply the result obtained in (2) above by the factor indicated below for the deflection sensitivity desired:
Deflection sensivity Multiply by
0.1 volt per inch 100
1 volt per inch 10
10 volts per inch 1
100 volts per inch VlO
(4) Apply the calibrating voltage to the Y-SIGNAL INPUT terminal and adjust the controls to give a stationary picture on the screen. Then adjust the attenuator switch (S201) and Y-GAIN VERNIER control until the peak-to-peak deflection of the signal on the screen is the same number of scale divisions (each scale division being %0 inch) as the result obtained in (3) above.
Measurement of Unknown Voltage.
(1) When the scope has been calibrated as in a above, the peak-to-peak value of any a-c voltage within the range for which the calibration has been made may be determined by applying the unknown voltage to the Y-SIGNAL INPUT terminal and observing the deflection on the scale over the screen. The positioning and frequency controls may be adjusted to bring the picture into a better position for reading, but the Y-GAIN VERNIER control must not be moved once the calibration has been made. The deflection ’sensitivity may be changed in the ratio of 10:1,
however, without affecting the calibration, by changing the attenuator switch. If the calibration was made with the switch in the 25-volt position, the deflection sensitivity is reduced to y10 of the previous value by placing the switch in the 250-volt position.
(2) For a sinusoidal voltage, the rms value may be determined by dividing the peak-to-peak value obtained from the oscilloscope measurement by 2.83.
15. D-c Voltage Measurement
D-c voltages are usually measured with a d-c voltmeter. In special cases, however, it is desirable to use the oscilloscope to reduce loading of the circuit in which the measurement is being made. The procedure is as follows:
a. Start the oscilloscope as explained in paragraph 11. Then turn the BEAM switch OFF.
Z>. Disconnect the jumpers for the vertical deflecting plates, Y1 and Y2, on the terminal board at the back of the chassis (fig. 3).
c. Turn the BEAM switch ON, adjust the FOCUS control, and observe the position of the sweep line on the screen. Then turn the BEAM switch OFF.
d. To measure an Unknown d-c voltage, connect it between Y1 and Y2.
e. Turn the BEAM switch ON and observe the position of the line on the screen.
/. Count the number of scale divisions between the two positions of the sweep line on the screen and multiply this number by 4 to obtain the reading in volts. An upward deflection indicates that the positive terminal is attached to Y2. A downward deflection indicates the opposite polarity.
16. Comparison of Unknown Frequency With a Standard
Since the frequency controls of the oscilloscope are not precisely calibrated, the instrument may not be used as an absolute frequency-measuring device. The only method by which a frequency may be measured is by comparison with a standard frequency such as the power line frequency or the output of a calibrated signal generator. Two methods are possible, one using Lissajous figures and the other using the internal linear timebase. The first method (a below) is applicable only to
10
sine waves. The second method (b below) may be used for any type of voltage wave.
a. Measurement by Means of Lissajous Figures.
(1) Start the oscilloscope as explained in paragraph 11.
(2) Turn the BEAM switch and COARSE FREQUENCY control to OFF and connect the standard frequency source between the X-SIGNAL INPUT and GROUND terminals.
(3) Turn the BEAM switch ON and adjust the X-GAIN VERNIER control until a convenient horizontal deflection is obtained on the screen.
(4) Connect the unknown signal between the Y-SIGNAL INPUT and GROUND terminals.
(5) Adjust the attenuator switch and Y-GAIN VERNIER controls until a pattern of convenient shape is seen on the screen. This pattern is called a Lissajous figure. Typical patterns are shown in figure 5.
(6) If the frequency ratio is large or not a simple ratio, the pattern is difficult to interpret. If the standard source of frequency is variable, it can be adjusted until a stationary pattern with a ratio of 1:1, 2:1, 3:2, or some other simple pattern is obtained. The frequency ratios of the patterns shown in figure 5 are expressed in terms of horizontal or X-axis frequency to vertical or Y-axis frequency.
(7) Inclose the pattern with an imaginary rectangle the sides of which are tangent to the pattern and parallel to the X- and Y-axes.
(8) At an instant when the pattern shows open loops, count the number of points at which the pattern is tangent to the vertical side and to the horizontal side of the rectangle.
(9) The ratio of the X- to the Y-frequency is equal to the ratio of the number of points of tangency on a vertical side to the number of points of tangency on a horizontal side or:
Y- frequency =
Number of horizontal tangent points
Number of vertical tangent points
X
standard frequency.
b. Measurement by Calibration of Oscilloscope Linear Timebase.
(1) Adjust the oscilloscope for observing waveforms as explained in paragraph 13 R263
O—O-j-4—। < i meg
n + J I | I [~^----1 1 -600V
0-0- L 71 k~ ---------- FOCUS I T J
X2 - IX ------—*< R262
________Jy2 s 50ok
”Z~t~ _______ I-------♦ -900 V
C237 __ZJ J
”----7 -------♦--------- — C 235 R 259 S 5> R 261
50MMF 1 ! ZOOK
0.1 MF ?
I lOFF
10 0 K ------ A 7) / /]/ SMALL GRID BIAS
i /1 / i//i //
s / 1/ // lzA
0 / / 1/ 1/ 1/ K 1/ . 1/_____DE-IONIZING POTENTIAL
/ e c
0 ------------------------------------------------------
TIME—*-
A.FREQUENCY CHANGED BY VARYING GRID BIAS.
EB +
SMALALRTIMECURVE /AxZtAcI CHARGING CURVE
S™*±T'ME / X LARGE TIME CONSTANT
CONSTANT / /
I
UJ ________dz b/ f___________________FIRING POTENTIAL
i .7 W 7
1A/V/V ___________/ / / / K________V OE-IONIZING POTENTIAL
e c
0 -----------------------------------—-----------------
TIME
B FREQUENCY CHANGED BY VARYING CHARGING CIRCUIT TIME CONSTANT.
TM2689A-I2
Figure 13. Variation of saw-tooth generator frequency.
generator used with Oscilloscope I-245-A is shown in figure 14. The thyratron tube, V205, is a type 884.
(1) A voltage divider, consisting of resistors R239 and R236, maintains a fixed positive voltage on the cathode of the thyratron, thus biasing the tube. Capacitor C216 bypasses the saw-tooth voltage wave around the biasing resistor R236.
(2) The frequency controls vary the frequency of the saw tooth by varying the time constant of the charging circuit. The COARSE FREQUENCY control, S203, is a nine-position, two-gang switch which selects the proper capacitor (C217 through C224) for the frequency range desired. The FINE FREQUENCY control varies the charging rate of what-ever capacitor is in the circuit by varying the resistance of R238. In the OFF position of the COARSE FREQUENCY control switch, the sweep generator is inoperative and the input of the X-axis amplifier is connected directly to the X-SIGNAL INPUT terminal. In all other positions of the switch the saw-tooth output of the saw-tooth generator is applied to the X-axis amplifier.
c. Synchronization.
(1) In order to obtain a stationary pattern on the oscilloscope screen, the period of the sweep must be exactly equal to the period of the waveform to be observed or some whole multiple thereof. If the lengths of the two periods are almost the same, the pattern will drift across the screen as shown in figure 15. The signal voltage shown is a sine wave whose period is slightly longer than the period of the saw-tooth sweep. In the pattern shown at A only the part of the sine wave included between zero and 1 will appear. On the second sweep the part between 1 and 2 will show, but it will differ slightly from the part shown in A. In the sweeps that follow, the picture continues to change and appears to travel across the screen from left to right.
(2) To synchronize the sweep so that it will have exactly the same frequency as the signal, a synchronizing signal is applied
24
LINE
EXTERNAL FREQ INTERNAL ----------
Q Q O FINE
FREQUENCY
R237 R238jT
6 --------------------------------—VA--------Wv------0 +■ -
_____ ___ ________________, 750K MEG SIGNAL 1 OFF
----------------3 6 -------3 0--------r--)|—°
SYNC SIGNALl ~^C215 8845 °y "---°x R233S
AMPLITUDE O.IMF ________O X o_O X. 5MEGS025MF
R234X-^VV\------(——e) ---O O * , 1 l~O <3----------O
IOOkS. R235 k ■——I J COARSE \
1 'OK X____/ ^r° [FREQUENCY! <>----o S2O3 \
REGULATED | I l_? 4 " ° _AVUtooth
+,595v - 0 3 o 8 i lfs----------------9 ? saoutpou°tth
?-6cm£o£s ___________ VOLTAGE
CM CM CM q ™ --------* y
J t o]_a> o]_- /
R236 x IK
-zL- TM 2689A-I3
Figure 14. Saw-tooth genera tor'circuit, simplified schematic diagram.
|O _ il !2 h '4 I5
& AAA/V V ! !
i ! ; I l
■ I i ;
SWEEP ! X\ /\ /\ /\ /
VOLTAGE ! / / / / /
APPEARANCE ON SCREEN
A B
E TM 2689A-I4
Figure 15. Apparent motion of oscilloscope patterns on screen.
25
P|Eb +
/~Ep VS Eg / / X
/ STATIC CONTROL /
/ CHARACTERISTIC / X
|\ / 7~ T\ T\ C\ FIRING POTENTIAL
1 \ ' ^ \ \ I LX VARIES WHEN
| \ / / \ \ \ SYNCHRONIZING
। \ \ \ \ SIGNAL IS APPLIED
■ V r
I \ I / I / / / / /-FIRING POTENTIAL
1 A / l/l/z/// WITH DC BIAS
; : _A_V__y_lZ_ZV_T__Ew
/ \ ^*“7 ^--EXTINCTION
1 I / \ FREE RUNNING ^SYNCHRONIZED POTENTIAL
_ [__________/_____\ PERIOD____PERIOD____f
E-q * | \ TIME -►
I u '-7-► \
1 *\
। / '—CAPACITOR
I I I ^D-C GRID VOLTAGE
। I . BIAS CURVE
1 Jzx
____I I ^'"—SYNCHRONIZING -------| 1 SIGNAL APPLIED
I TO GRID '
1
cT 1 l"""—J
! r" ।
F-4 ।
TM2689A-I5
Figure 16. Action of synchronizing voltage applied to grid of thyratron.
to the grid of the thyratron. The effect of this synchronizing voltage is shown in figure 16. The first two cycles of the saw tooth show the condition when no synchronizing signal is applied. The line Ef represents the firing potential of the thyratron and line Eex represents the extinction or de-ionizing potential. When a sine-wave synchronizing signal is applied to the grid, the firing potential varies with the synchronizing signal as
shown by the sine-wave portion of the 1 ine Rf. When the grid voltage goes positive, it is easier to fire the tube, and the firing potential falls. When the grid voltage goes negative the firing potential rises. The capacitor voltage curve now reaches the firing point at the downward portion of the firing potential curve instead of at the d-c bias firing potential as before. A new cycle of the saw tooth is started for each cycle of the synchro-
26
liizing signal, and the sweep is thus exactly synchronized.
(3) In Oscilloscope 1-245-A the synchronizing signal from the SYNC SIGNAL SELECTOR switch, S202, is applied through coupling capacitor C215 to the potentiometer R234 (fig. 14). The amplitude of signal fed to the grid of the thyratron is determined by the setting of R234, the SYNC SIGNAL AMPLITUDE control.
(4) The synchronizing signal amplitude must be kept as low as possible during operation, because too much signal causes distortion. The reason for this is shown in figure 17. With a small value of synchronizing voltage the firing voltage is represented by the solid curve BDF. The rise of the saw tooth reaches the firing potential once for each synchronizing cycle, at B, D, and F, and the sweep is synchronized with the signal. If the synchronizing signal is increased so that the curve of the firing voltage is along the dotted curve GIKM, the rise of the saw tooth reaches the firing potential three times for each cycle of the signal, at G, I, K, M, etc., and starts a new cycle each time. This causes distortion of the sweep and of the pattern on the screen.
(5) The synchronizing signal may be taken from any one of three sources, depending on the setting of the SYNC SIGNAL SELECTOR switch (fig. 32).
(«) In the EXTERNAL position the signal is taken from the EXTERNAL SYNC SIGNAL terminal.
(&) In the LINE FREQ position the signal is taken internally from one of the low-voltage secondaries of the power transformer. This applies a sinusoidal synchronizing signal of power line frequency.
(c) In the INTERNAL position the signal is taken from the output of the final stage of the Y-axis amplifier (par. 35 \ XI X 1 Gjz< X I ZuX X/ X^
\ / X I. / Xx \ / xX \ / । \ >X\ ' s'/
DEIONIZING X \ 1XX \ Xb^X
POTENTIAL "A- " ~\ HCJL \~E-------------------
O--------------(---------------------\-----------------------
SWEEP WITH SMALL SWEEP WITH LARGE
SYNCHRONIZING SYNCHRONIZING
VOLTAGE VOLTAGE
r,..r- TM2689A-I6
I I M t. ।
Figure 17. Distortion of sweep resulting from too much synchronization.
27
<\ + /\...
i /-------V /11J11\f ? T T-rr
V W - W
\ ib /
/--N. 2-.
N. 3-A. 4
\6-.
TIME X,
r &-■ Al
9 -- X. io- nL //■• Nt
12-■ aI
--------A--------A
.....................................A a:-w +'M - vF
/--
>1 2-
3" N. 4-5-TIME >U-
6 XL 9-- Nt IO- xl //-- XI B
_______'i::___TM2689A-I7 ----------------
Figure 18. Distortion of pattern at high sivecp frequencies.
28
larger proportion of the time of one sweep cycle as the frequency of the sweep is increased. This causes a distortion at high sweep frequencies as shown in figure 18. Assume that the fly-back time is 10 microseconds and that the period of the sine wave in A, figure 18 is 600 microseconds. The flyback time is 10/600 or 1.6 percent of the period of the sine wave, so that 1.6 percent of the sine-wave cycle will be distorted on the screen. If the frequency of both the sweep and the applied signal is multiplied by 5, the period of one cycle is 150 microseconds. Since the fly-back time is still 10 microseconds, it now represents 10/150 or 6.6 percent of one cycle. In B, figure 18, 6.6 percent of the sine wave is distorted. To avoid this difficulty the sweep frequency is made a submultiple of the signal frequency so that several cycles of the signal appear on the screen. Only the last cycle is then distorted by the fly-back, and the others are accurately reproduced.
34. X-Axis Amplifier (fig. 19)
a. Input. The X-axis amplifier consists of the two sections of tube V206 (V206A and V206B) connected as two cathode followers. For normal
✓
operation, the input of this amplifier is connected to the output of the relaxation oscillator in order to obtain the necessary sweep voltages. External signals may be applied to the X-axis amplifier by switching the COARSE FREQUENCY control to the OFF position. This connects the X-axis SIGNAL INPUT terminal to the X-axis amplifier. The input resistance of this terminal is approximately 5 megohms shunted by a maximum capacity of 34 micromicrofarads.
b. D-c Circuit. The platesof V206A and V206B are connected to the regulated 155-volt supply. The cathode circuits are returned to —280 volts. The negative cathode return is provided so that a range of positive and negative voltages for positioning is available. The functioning of the positioning circuit is explained in paragraph 38.
c. Ouput. V206A acts as an impedance-transforming vacuum tube stage and feeds its signal, output through capacitor C225 into the low-impedance, constantly variable GAIN VERNIER control R241, thus eliminating much frequency discrimination usually found in such controls. The output of the GAIN VERNIER control is then applied to the grid of V206B. By means of the GAIN VERNIER control, which is located in the lower right-hand corner of the front panel, the over-all gain of the X-axis amplifier (including the paraphase amplifier) may be varied from zero to approximately 35 times. The amplifier has a flat frequency response plus or minus 10 percent from 2 to 100,000 cps.
♦
°|X SIGNAL INPUT|
C2I4 155V
^025MF
(1_________ V2O6A i * I V2O6B
>R233 .ioFF 6SN7GT _d^\
fOO F f] /vv 0237 no
T0 ---------1 x v 50MMF u u
SAWTOOTH ---------------fZCrr: ~<-------------------------—.-.CRT
GENERATOR C225 i I GR,D
2 °< A: R243 >1
25OK< 8MF |5kS.... —*~T0 X AXIS ?IOOK
< > I X I PARAPHASE K'UUK
R24I p | | I POSITION | AMPLIFIER
500K<"* V *v,c I < X1AX'S <>R242
| GAIN \
I VERNIER < 300K
-28°V -280 V _|080v
TM2689A-I6
Figure 19. X-axis amplifier, simplified schematic diagram.
29
d. Blanking Circuit. A saw-tooth output from the cathode of V206A is taken through capacitor C237 to the grid of the cathode-ray tube for blanking out the sweep during the return trace. The circuit is shown in figure 20. Capacitor C237 and resistor R258 have a small time constant and constitute n differentiating circuit since the output is taken from across the resistor. Capacitors C238 and C239 bypass the wave around the power supply and have no effect on its shape. A differentiated saw-tooth wave is a rectangular wave. The linear change of voltage of the sawtooth makes C237 charge with a constant current.
C237
—IF—r---------------
50MMF J I
<^7 R 2 58 I “1030 TO “1080V
INPUT <^IOOK ..I/
X \ / \ I /" “T“ 0238
/ \x \ I t oimf X I____ 1_____1 “1080 V
“L I C239
— ZZZ 05MF
•------------r~T
■e
s' !\ y' i\ i\
SWEEP VOLTAGE / [ \ / | \ / I \
। W । r ; \
o'--------tt-------------1-----।-------------;t
I INPUT VOLTAGE | । ,
1 1 I ' i B
CATHODE _ __ [_ _J
VOLTAGE " 1______ ~ f
GRID VOLTAGE "10 00 V ~
OF C.R. TUBE co--------------------------------------------------
♦ GRID VOLTAGE q
TM 2689A-I9
Figure 20. Blanking circuit, simplified schematic diagram.
This current flowing through R258 produces a constant voltage drop. When the charging current reverses direction, a constant voltage drop in the opposite direction is produced. During the rapid fall of the saw tooth, a large negative voltage appears across R258 and drives the grid below cut-off. Thus the spot is removed from the screen during the fly-back time. Under certain conditions the blanking pulse is not required; it may then be removed by opening switch S204. which is located on the rear terminal board (fig. 3).
35. Y-Axis Video Amplifier (fig. 21)
a. Attenuator. The signal to be studied on the Y-axis is connected between ground and the Y-axis SIGNAL INPUT terminal located in the lower left-hand corner of the front panel. This input connects to the Y-amplifier through a 10-to-1 attenuator that may be switched in or out of the circuit by means of switch S201. This switch is labeled Y-GAIN and is located in the lower middle of the front panel. When the attenuator switch is in the INPUT UNDER 250 V R. M. S. position, the input is applied to the attenuator circuit. This circuit is a frequency-compensated voltage divider; R201 and C202 form one section of the divider, and R202, R203, and C203 form the other section. The circuit is adjusted by variable capacitor C202 so that the time constant of R201 and 0202 equals the time constant of R202, R203, and C203 plus the input capacitance of V201A. This adjustment makes the attenuation constant for all frequencies and prevents the distortion of nonsinusoidal waves. With S201 in the INPUT UNDER 25 V R. M. S. position, only R203 is in the circuit as a grid leak and the signal is not attenuated. In this manner no more than 25 volts rms is ever applied to the input section of tube V201. Switching to either position of the attenuator has no effect on the input impedance of the Y-axis amplifier SIGNAL INPUT terminal, which remains constant at approximately 2 megohms resistance and 40 micromicrofarads capacitance.
b. Cathode-Follower Inbut Stage. V201A is connected as a cathode-follower stage. The cathode-follower input stage is used because the input impedance of this type of circuit is very high and because the danger of distortion, caused by drawing of current by the grid, is minimized. Since the gain of the cathode-follower is less than 1, the applied signal appears across resistor R204 with less amplitude than at the input but with the same waveshape. Since the cathode follower is normally conducting, there is a direct voltage at the cathode. The impressed signal causes this voltage to vary. This varying voltage is coupled through capacitor C205 and appears across potentiometer R206. Capacitor C205 is large (8 mf) because it is desired to pass the very-low-frequency components of the signal. Since the slider on potentiometer R206 can select any desired fraction of the signal voltage. R206 serves as the
30
+ 155V
\ R2II J> R212
/ 24K < 24K
C207 C208
*"30^ J 30 MF^
JS> L20I DO L202 '
| Pl.8-4.2 || Pl.8-4.2
1 MH | MH
C20I j> J>
'“F S R 213 *> R2I4
O---1 ( --------♦---- \ 6 2K \ 8.2K
Iy-signalI > s
INPUT _Z_ C202 IMF IMF
2 MEG < 7 " 3-30 MMF______ ( >________| £_ >___। £_____
IlNPUT UNDERl 1 zH X ~^V 202A s' -sV202e ■>. V20IB
I 25 V RMS | ,, f -*■" \ . V20IA ( -J- X ( \ A 1 AQM7CT
o (— ~ \ 16SN7GT FT-----) 0 ( 1 ------I—■— j26SN7G
[INPUT UNDERl r, J> ----S |lA?IS ' ' >—S
I 250V™S I V >2RM2E°G3 ■ , VERNIER 46SN7GT> |65N7GT
\ <1---- ( . I D_.. > R2I6 > TO PARAPHASE
S R2I5< I < AMPLIFIER—►
S I C2O5 I MEG > \Yu >
P 8MF < 5IK <
> L --------o
____o /R204 >4 <•- < R2 07
X> > I00K P-*-I P 15 K____
>R202 I R2C9 |y-position|
C203 p^ P 200K 1, < IOOK \ C209 P 240-n- <1 MEG
200MMF > < 1--- (------1 > P P PL
I R2I° < 00<» | I S R208
> 240K 24an- MF <
----•-------<1 > 240K \ 3Q0K
h -280V
■==■ U 6 -280V
-------- ------< I>—•-----------!-
TM 2689A-20
Figure 21. Y-axis video amplifier, simplified schematic diagram.
gain control by varying the input signal fed to the grid of V202A.
c. Video Amplifier Stages. The two sections of tube V202.(V202A and V202B) are compensated video amplifiers. In order to make the amplification more nearly uniform over a wide band, frequency-compensation networks are used.
(1) High-frequency compensation. Plate load resistors R213 and' R214 are much smaller than normally would be used to give increased bandwidth. Inductors L201 and L202 are used to compensate for the effect of tube interelectrode and stray wiring capacitances at high frequencies". Without L201 and L202, the effect of these capacitances would be to shunt out high frequencies. Since the impedance of L201 and L202 increases with frequency, the effect of these capacitances is minimized. When L201 and L202 are properly adjusted, the effective plate load iippedance and the gain of the two stages
will be nearly constant up to 1 megacycle.
(2) Low-frequency compensation. Low-frequency compensation is given by resistors R211 and R212 and capacitors C207 and C208 in the plate circuits of V202A and V202B. Without these circuits, the gain of the amplifiers at very low frequencies would be reduced by the loss which occurs in the grid-coupling circuit. At high frequencies, resistors R211 and R212 are bypassed by the low reactance of capacitors C207 and C208 but at low frequencies the reactance of C207 and C208 is high. Thus, for low frequencies the plate load resistors are effectively much larger, since a low-frequency voltage is developed across R211 and R212 which' is not bypassed by the capacitors. Since the gain of the two stages is increased by making the effective plate load resistance larger, the attenuation of very-low-frequency
31
voltages in the input circuit is offset. In this manner the low-frequency response of the amplifier is extended down to nearly 2 cps. Without capacitors C207 and C208 and resistors R211 and R212, the lowest frequency that would be amplified with the midband gain would be approximately 30 cps. Because the amplifiers have very good low-frequency response, the operator should bear in mind that any low-frequency components in the signal under consideration, such as may be introduced by switching, etc., will be amplified and will appear on the screen. This usually causes the trace to disappear for several seconds. The return speed of the trace depends upon the time constants of the coupling networks.
d. Cathode-Follower Output Stage. V201B is the output stage of the Y-axis amplifier and is connected as a cathode-follower circuit. The input impedance to a cathode follower is high and the input capacitance is less than for a conventional amplifier. This low’ input capacitance
makes it possible to extend the high-frequency response of the amplifier, since the shunting effect of the capacitance is minimized. The signal appears across cathode resistors R207 and R208. R208 returns to a — 280-volt connection, but, despite this, the tube plate current passing through the two cathode resistors is sufficient to make the cathode slightly positive with respect to ground, and the grid will not draw any current. R208 is returned to a negative voltage in order to make the lower end of R207 negative with respect to ground and the upper end positive. This makes it possible to fix the grid of V203 above or below ground potential by adjustment of the Y-POSI-TION control R207 (par. 38).
36. Paraphase Amplifiers
The two paraphase amplifiers (one consisting of tubes V203 and V204 in the Y-axis circuit and the other of tubes V207 and V208 in the X-axis circuit) are similar in circuit arrangement and operation. Their action is explained in relation to the X-axis amplifier (fig. 22).
C226
0.5 MF
R246
---------vW----------i------f-----------
750 K
L 205
O+I55V H.6-23.4MH
V206B T V7O7
4-6SN7GT 6V6GT ° r \AA?
©S' \ R245
/ \ 25 K
| j| <^R25l
---------\—"■■■■ / > 5 MEG
\> V2I5
I CATHODE RAY TUBE
| 1 > yW • *f °____________ I I I j
I50K \ I I /
—— R252
R242 > ~ /1 |\ 1 5 MEG >
300K <■ f_______\ I °
> |-----f-•■■■■ I + 20OV -1,200 V
\ ""T"" J S' R253
O ■ X. S R249 s. 5 MEG
-200V 25K
V208 < ►—y OOQ >------\AA?—
6V6GT -
L206
11.6-23.4 MH
R248
---------• -----------------*----------------------------
750 K
C227 TM 2689A-2I
0.5 MF
Figure 22. X-axis paraphase amplifier, simplified schematic diagram.
32
a. Inputs. The saw-tooth voltage wave applied to the grid of tube V207 produces across resistor R244 a voltage wave of the same shape and polarity but of approximately half the amplitude of the input. This voltage is used to drive tube V208. Since it is a degenerative voltage for V207. the voltage effective between grid and cathode of this tube is approximately half of the input voltage. Thus the input voltages to the two tubes are nearly equal, but of opposite polarity with respect to the grids, so that the outputs of the circuit are two voltages of approximately the same amplitude but of opposite polarity.
6. Outputs. The plates of the two amplifiers are directly coupled to the deflecting plates of the cathode-ray tube to prevent attentuation of the low-frequency signal. In order to maintain the deflecting plates at approximately d-c ground potential, the two resistor networks, R250, R251, R246, and R245 in the circuit of V207, and R252, R253, R248, and R249 in the circuit of V208, are connected between —1,080 volts and +280 volts. Chokes L205 and L206 give high-frequency compensation in the same manner as L201 and L202 in the Y-axis video amplifier (par. 35c(l)). Added high-frequency compensation is given by the R-C combinations of R246 with C226 and R248 with C227. Because the impedance of the R-C combination for high frequencies is less than for lower frequencies, the higher frequencies are coupled to the deflecting plates with less attenuation than the lower frequencies.
37. Operating Controls
With the exception of the blanking switch, the external blanking input, and the deflection plate terminals, all the controls of the oscilloscopes are grouped together on the front panel and their functions are plainly labeled. The beam controls are all located on the upper portion of the panel, with those of the sweep circuit in the middle and the amplifier controls at the bottom. Conventionally, the vertical deflection controls are located on the left side of the panel and the horizontal deflection controls on the right side.
a. Power Switch. The power switch controls the power input to the oscilloscope. When the switch is in the ON position, the pilot light located at the bottom center of the front panel should glow, indicating that power is being applied to the instrument. This switch should be thrown to
the OFF position before the oscilloscope is removed from the case.
6. Intensity Control. The setting of the INTENSITY control determines the bias on the grid of the cathode-ray tube and thus the amount of beam current drawn. Use as low a value of intensity as is conveniently possible to prevent burning the screen and to increase the life of the tube. A bright spot must not be allowed to remain stationary on the screen or a discoloration of the screen will result.
c. Focus Control. By varying the voltage on the second (focusing) anode of the cathode-ray tube, the FOCUS control causes the electron beam to be focused to a point at various distances from the electron gun. The correct voltage on this anode will focus the electron beam to a point on the screen of the cathode-ray tube, thus giving a fine trace. In general, the electron beam will be exactly in focus in only one portion of the screen for a given setting of the FOCUS control.
Caution: In order to prevent burning of the screen, bright sharply focused spots should not be allowed to remain stationary.
d. Beam Switch. The BEAM switch blanks out the electron beam by biasing the grid of the cathode-ray tube to beyond cut-off. This is convenient for stand-by operation where it is desired to have the instrument ready for immediate operation.
38. Position Controls
The Y-POSITION control permits the adjustment of the trace on the Y- or vertical axis. This control is used mainly to adjust the trace to some particular portion of the calibrated scale that is mounted on the face of the cathode-ray tube. The X-POSITION control permits the adjustment of the trace in the X- or horizontal direction. The direction of the shift is marked LEFT or RIGHT on the panel.
a. Since the deflecting plates of the cathode-ray tube are directly coupled to the plates of the paraphase amplifiers, the average d-c voltage on the aplifier plates acts as a positioning voltage. The X-POSITION control is resistor R243 and the Y-POSITION control is R207 (fig. 32). Since the operation of both circuits is identical, an explanation is given in relation to the X-axis para-phase amlifier circuit.
6. V206B (connected in a cathode-follower cir
33
cuit) is designed so that there will be a point at about the middle of potentiometer R243 at which the voltage to ground is zero. When R243 is set at the ground potential point, the bias on V207 must be exactly the same as the bias on V208. Under this condition, and with no signal applied, both tubes conduct the same amount of current and the voltage at the plate of V207 is the same as the voltage at the plate of V208. The spot will then be in the center of the screen if the electron gun is accurately aligned.
c. If it is desired to move the spot to the right, the slider on R243 is moved up so that the grid of V207 becomes more positive (fig. 22). This increases the current through tube V207 with the result that the cathodes of V207 and V208 become more positive. When the cathode of V208 becomes more positive, however, the bias on V208 is effectively increased and it passes a smaller value of current. Therefore, since V207 is passing a larger current than before the V208 is passing a smaller current, the average voltage at the plate of V208 is more positive than the voltage at the plate of V207, and the spot is attracted to the right toward deflecting pl ate X2. In a similar way it can be shown that the spot will move to the left, or toward deflecting plate XI, if position control R243 makes the grid of V207 negative with respect to ground.
d. Movement of the position control potentiometer has very little effect on the gain of tubes V207 and V208, since the actual shift of bias is so small that the tubes will work on the linear part of their characteristic curves. The over-all gain is affected slightly because the amplitude of the input signal to V207 varies somewhat as the slider on R243 is moved. Since R242 is large compared to R243, however, most of the signal voltage is developed across R242 so that the over-all gain is almost independent of the setting of R243.
e. In the Y-axis circuit the spot is moved toward Y1 when R207 is moved in the more positive direction and toward Y2 when R207 is moved in the more negative direction.
39. Power Supplies (fig. 32)
a. A negative potential of 1,080 volts is furnished by V214, a rectifier Tube JAN-5R4GY connected as a half-wave rectifier. The output is taken from the two plates connected in parallel and is filtered by the resistance-capacitance filter
R264, C240, and C239. The a-c voltage for this rectifier is obtained from the portion of the high-voltage secondary (on transformer T201) included between the filament circuit of V214 and the grounded terminal of the winding.
b. Positive 280 volts is furnished by V213, a rectifier Tube JAN-5Y3GT connected as a fullwave rectifier. The output is taken from the center tap of the filament winding for V213 and filtered in the two-section pi filter consisting of L208, L207, C234, C233, and C232. The plate winding for this rectifier is the center-tapped portion of the high-voltage secondary, to each end of which one of the rectifier plates is connected.
c. Negative 280 volts is furnished by V212, a rectifier Tube JAN-6X5GT connected as a halfwave rectifier.
The output is taken from the two plates connected in parallel and is filtered by the resistance-capacitance filter consisting of R257, C231, and C230. This rectifier has a separate center-tapped filament winding with the center tap grounded. The d-c return is to the cathode terminal (pin No. 8) of the rectifier tube. The a-c winding for this circuit is that portion on the high-voltage transformer between tap T2 and T1 (ground), tap T2 being connected to the cathode terminal of the tube.
40. Voltage Regulator (fig. 23)
Part of the output of the positive 280-volt power supply is regulated by the voltage-regulator circuit consisting of V211, V209, and V210. This regulated voltage provides plate voltage for the amplifier tubes. The purpose of the regulated voltage is to prevent movement of the picture on the oscilloscope screen such as would be caused by power line fluctuations. The circuit is shown in figure 23 and its operation is as follows:
a. The output voltage of the regulator is developed across the 1-megohm voltage-regulator adjustment potentiometer R254 in parallel with the resistance of the load. These resistances make up one part of the total voltage divider. The other resistance, through which all of the load current must flow, is the plate resistance of tube V211. The other elements in the voltage-regulator circuit are used to control the resistance of V211 and in this way maintain a constant voltage across the load.
b. The cathode voltage of V211 is the regulated
34
output of the regulator. The cathode potential of V209 is held at a constant positive value by regulator tube V210. The grid potential of V209 is a voltage selected by'potentiometer R254. This potentiometer is set so that the grid voltage is less positive than the cathode by an amount (the bias) which causes V209 to pass a certain plate current. This plate current flows through plate load resistor R256 and causes a drop across it. The magnitude of the voltage across R256 is the bias on tube V211. Therefore, the adjustment of potentiometer R254 establishes the normal resistance of V211. This adjustment is used to set the value of load voltage which the regulator is to maintain.
c. If the load voltage tends to rise, whether from a decrease in the load current or from an increase in the input voltage, the voltage on the grid of V209 also tends to rise (become less negative), the cathode voltage remaining practically constant. Tube V209 then conducts more current because the bias is smaller. A greater current flows through R256, which causes a greater voltage drop across this resistor. This voltage, which is the bias volt
age for V211, causes the plate resistance of V211 to increase. A larger portion of the available voltage appears across the higher resistance of V211, and the load voltage remains practically constant. The action is similar if the load voltage tends to fall.
cl. A pentode (Tube JAN-6SJ7) is used for V209 because of the high amplification possible with this type of tube. The use of the pentode makes the output voltage much more constant, since small variations of load voltage are amplified sufficiently to cause operation of the circuit.
e. The anode of the regulator tube, V210, is connected to the cathode of V209 and to the regulated voltage output through resistor R255. V210 must be connected to the B-r supply in this way in order to cause the gas in the tub to ionize when the power supply is first turned on.
41. Primary Power Circuit (fig. 32)
a. Power for the oscilloscope is applied through a 1.5-ampere fuse, F201. interlock switch S208, POWER ON switch S207, and line voltage selector switch S206 to the primary circuit of power
35
+ 28OV
O
V2II "
6V6GT
ff-------------------♦--------f---------♦-----c +15 5 V
REG
<> R256
<> 5I0K
< 0229
----------------° V209 Timf
___6SJ-7 _[_C228
f X IMF
I — — -----1-------<, < R254
\ — — — -4-----------------*-----►< I MEG
I VOLTAGE
P255 REGULATOR
o , a. A a.______ ADJUST-
MENT
V2I0 1--^ 8-2K
VRlO5-3OyX
\Q/
TM 2689A-22
Figure 23. Voltage regulator, simplified schematic diagram.
transformer T201. Switch S208 is mounted on the rear of the chassis (fig. 25) and opens, breaking the circuit, when the chassis is removed from the case. Transformer T201 has two primary windings. Switch S206 connects the two windings in series for 230-volt operation or in parallel for 115-volt operation.
1). Transformer T201 has five secondary windings which supply all the voltages needed for filaments and rectifiers throughout the circuit. The windings are as follows:
(1) One 6.3-volt winding (F7-S7, fig. 32), insulated for high voltage, supplies the filament of the cathode-ray tube.
(2) One 6.3-volt winding (F6-S6, fig. 32) supplies the filaments of the voltageregulator tubes V211 and V209.
(3) One 5-volt winding (F5-S5, fig. 32) supplies the filament of rectifier V213 and is center-tapped to provide an output connection for the direct current from V213.
(4) One 6.3-volt winding (F4-S4, fig. 32) supplies the filaments of all remaining tubes in the circuit except V214. This winding has a grounded center tap, and the pilot light, 1201, is connected across it.
(5) The fifth winding is a high-voltage winding with five taps. It supplies the following :
(a) The 5 volts for the filament of V214.
(3) The 815 volts' for the high-voltage power supply.
(•yjif JSr JKM
■ WMNOwSMHMK*^^'"Pfl^SMBfe^awECBi..?
’a
_ e
I MLa L—J—F l^a
1 f MB
|r J:-,___^UI^MJIHBIMH__\______________________• i.
t afl ; j । \. n ~i
„——----• ■ • -. ._„^_J_. . .. --—-.J . .~- 1 * . I--
SkG ..,.. C"225 . S~206 <■. T~20l . ' P-254 . , C*232 . . . ■ . :
TM 2689A-25.
Figure 26. Right side of oscilloscope chassis.
39
|p „.. ,?|. .-—-r"^ : ZZ—
FJl
C .i...P:, ,,,.... ...... .liiMinim^MMiMmigL.-Jtt'...~~_m~——'’^-'■■■^■'-^ -■'--'''■■-'-■'-'™’ ——
'y^ ''v ■' -fwH
g|| ipfe' • ■-^®wllR|-'| B-
.... W..........................■ - IM M
C) s. T
* i ,<3 ’ wS^SBh Sf
I _ r<££j M*j V r fa
Liii—jj- " Linir*'jjhim jumii^^m I**
1/| * i lk
” r nl?Wu. o r
: ; • ! I | ! I ' ' ■
^‘c240, I R225 lR239 I 02l0oL c20i
, R24t> C2«9 C234 C2I6 RZIS «M.»»-M .
Figure 21. Left side of oscilloscope chassis.
40
41
B SOCKET OF ,F
V / ‘F- CATHODE-RAY TUBE —1|
S' B I fl
g^yL204 L2O6 1
•4i>4
Asm? -^wk-jaw WOBBIK
WlKBIUjwBfr'JSQW 1^ «
t1 on^ “—-, ^c. ' ■ fKa <^i^. -Wit f
,—eaaw^r-wii^^SffS ‘ iBi JL-8'256
" 1 ~~^ffl,M~EBt~—v : c'2?8 ■ I
s' ' I j V-214 h vW }" * 1.
X I hff TaWSk/B^ 1PS& _.-F—v-2io
V204 | W ^-^V208
I i .... ^^R254 I VqS . ’ Wlju
1 ' * £v R-257-—4- _-t-"c"25!
iWr*"——S206 |ir^
fcZ’ ’ C-23CK 1 ' jr - " - -
1 collar r---->..„ ___
•ci / C-209—4—S' -C-206
\ IK-' R’2,° r *' 4«-205
\ liSif < i ..
v . \ / ,. R-267^1_^ il -f^^FL-r-”'240'
i ^OR:»-x-aw'^ i R-209" I aes^O^&OMStZ— L ,,, 1 W • ■ • < fc-*' < % --r~fR-232
1 t i | R-204-" 1 -
* FX208<
CLAMPING SHIELD SHIELD ON W
RING SUPPORTS CATHODE-RAY TUBE ■■■■■■■■■■■■■■■■■^
TM26S9A-27 F«
TM2689A;28J
Figure 28. Top of oscilloscope chassis.
Figure 29. Top of oscilloscope chassis, cathode-ray tube removed.
C2I4 flliliiB
TM2689A-30,
S208 F20I
C233
C232
V2II
V2I2
LINE CORD
L207
L2O8
C239
C240
V2I3
T2OI
V2O2
C2O5
C207
C2O8
V209
R254
S2O6
V2O5
C225
C22O C2I8
C22I C222 C2
C224
V2O
R234
R2O6
C2I7
V2O!
C202
R203
C2O!
Figure 31. Bottom of oscilloscope chassis.
42
’—— —HBiiicAii \
v'z°3tw18PP®EFf_v'207
4l^XLJJKiw’ [ SmLBp' ' ^E-c=,r-g!
s-202. 7^5?. A"234
s-posJ#* QM-'C-M
5-205--’HwS
— R"243
R-207 -"A f 1 •
i®- / / Ml
R-260
[ R-261 R-262 R-208 _M 2S89A „9
iw 4va3M~zy
■ ■
Figure 30. Top of oscilloscope chassis, rear of front panel.
E._______________ 4-1557_____________________________________ + 280V
37 C2O825K R22Oi________________________________________________________________V-203, V-204, V-2O7, AND V-2O8 SHOULD BE MADE
f-« )|—1 J 25K > WITH R207 AND R243 ADJUSTED TO ZERO VOLTS AT
-T-yr+t ..+85V L2O3|!C> _____________________________________GRIDS OF V-203 AND V-2O7.
=■ 3 7.5-15 K Oj|.L204
~L202g MH 7.5-15
1-8-4.2 j \ 5 Z>|| MH
mh r1 r
JR2!6 +IOOV 5CPI
,o ’6ovkzn?5,ck206 v’2is v—----------JJ o52f
3-3OMMF | 1 U 6SN7GT p-2K C206 26SN7GT V.2O4 \---- Z^~1 •
Y-AXIS T-^-l- 2 26SN7GT 2 7171 7777~1 H„ +8°\ rvact +8°V 6V6GT \ ,__, I--- -
, Xlb C20I V-20IA J___ V-202A* J_MF V-2O2B 5p-------° .--, 3 6V6GT 3.--- 1 /
SIGNAL IMF R20| 7^«^ >---- — 'MF _1_ l*J^—— ------------4----. / F7, -I-
1 N PUT Q---1(--------------------- -------LL_Zh v 4 A ] l4- ) ~ -h/jxX \ | I ~ ' 5R4GY o|' ■=■
[Input under ^rmsI^ 3 SAj+'5V HtW/ ^7 ------------------------------------- . 6 StR
[INPUT UNDER 250V RMS~| QS20I '^-6AIN1 8mf J^q® F4 S4 1240 F4 Q +| ~ 8 " [—<'__1>~♦ ~I -- R258 -1,080V ^K^ /d?\8— ----X
---------1 < R203 i >Z^05J - +0.8V R2I5 . +6.8V--------------f4 s4 F4 -4 GRID 1 ~ —- 9 W .0.,0-Y— 11 I vf Sv *Z T20I C203 T |ZMEG +ZIV,r^VXZL_ rnrona^’MEG -J— > -°iR207 - --5 9? Qyo Q J V I 2-J_C238 A R260-\ T Y, . 5V T,<+
C2200 -L >R202 I ^R204 Y-AXIS— jR2IO-h2O9> ~=- ? £1 I5K______ +6 5v C2'2 J Y { | X2 I | | i ~T~I -pO.IMF |J iook xT/21------------------------------------r-^,
MMF 'T ?200K“^T >IOOK gain <2467ooO5 R209 ZT R22l> °--- ? -------<> f A | 1 TyiL fl | J ("4 I RFAM I I [|NTFhsiTv| '' ~^4 I
L_£ - e^j R222 WU \M [ f Y"? f 'I W ra Tvi^----
_________ — R205l A 24m4f ~ ~ — R208 =■ 7®° i 0.5 T/I------------.Tt, ____ F7 S7 i J — °5MF Ll2-^ <£? [GROUND] Q—^ 240K i ^24 ' R0K * MF R._fel R230 <►-RR05 Hook 385V g IK
N-Z —I— I ___________________-280V > R223 470K 470K / O-----(>2OOK I S) |)O O- 230V
__________________________________________________________________ —— c235 -L_______________r-4-+i+r<+r S205 ______________________________________________________________________________________________________________________________________________________ _--R224 1 R22,61-0.1 MF 'T' IMEG^_| [ __ +7 385 V S' | -
5 MEG> > C236 ’J R262 X * I 3 I |
-----------]|------L * SOOK |/_3 p5-------------------------------------j-3 I
R225J R227 > GOIMF -L C237 | 1FQCUS| 4k • ■ / S3 I F| O->
5MECi 5MEGf °'° 'T'SOMMF I 600v XV F6*--------------------------------------W ]C-_4(
f-------------1—1 t °S204 £ 5.2V S |jS 115V
_ R232 5RMEgI 5M5eU 'P Bs^'tcuG iR! mVg______________S6 TEST____________________________________________________________________________________________________________________________________________________________________________________________ I0K > S || SWITCH — F5 ]\Z
SIGN AL| \ J ---------►— F4 J । . t-SI
_1_ 1. 310V T5 Sj “
'-T' C2I3 R25I J R2 53 i 1 -----------------------------------------------°J ----- \A
T O.IMF 5MEG| 5MEG > 'l . P0*ER \6
—1— > |i ---------------' ON \ S207
-=■ I20K S5 ------- \’tW'
— . " " & “1^1 I
COARSE ”----------- |. -^r <3
FREQUENCY A 1 __________________________________o_~________J
X.X| C2I4 z -JJlH'------------------------^ZZZZZZ -~Z^- T-_Z--_-Z.Z--_Z-Z.Z-Z.-Z zzzl S4 |6
X~AXIS ___ D.25MF r .X ___I________ - I INTERLOCK!-1 ....
SIGNAL] rx_____________|Z ______________OFF C7 S203 '--------------------------------------------------------, L207 L208 I ®X?5®T SWITCH L S203
INPUT Ik | T7 9* 11 I8H I8H . 7 V‘212 9
11 L2o=4 ,50“ . i;!L206 n- i
S202? __________ SWEEP ON +25V ----- --- ll.6-23.4hK offill6-234 ,6V6GT * ___ILZo-soov F20I /
SYNC SIGNAL X> JO O FREQUENCY II MH I'Pp^R 0226 C227 <3 ' mJ 3 V-2II 71 ° °UU* U
02,51 L-ec™j 884 «oz j—o -WL+ T°4?^r .Yrh °-5“f L- !
"F I R235V-20^^ PI^OQ'VYSTi------------------------JZJ 6SN7GT 2 V'^OOB fBOvLZZJ UH^'+bOV 5,55 TOi---------------------------------------------------- 0230 f T ’
---------- lOOxF’--^ MP Z # Z ? tz; I rAl ?5 I P^I~T ,____16V6GT C228 C229 I f—<- „c?5I0K '6MF 40-60 CYCLES I sync signal! >-y-1—1—a——®—1—1—1—T L /Czl3 1 8 [ \Z J4 5 7 11 mf imf L +l45 _ —1—
> [ AMPLITUDE l2jfTB23J]*4.9vj*gjOZ_Z^K,^ Tt" 11 “Z® tB^vl t5 e+[t +' T T V’2O9 ~
•i I 4 IK 4 C2.OFS?~§S!§S!^S!? f’4 'i ‘ I 1 ■ H 6SJ7
o---- g « * ,»-------------f'SK F4 S4 +6,2V S4 F4 >5 -28OV
C225 -6.5V |X-POSITION| R^An^Tnp 2A7 ADJUST R254 T0 GIVE 155 v AT
h40°K . Te“F U42 H
________. Z-X VookF1------ I “ i--------------------------------------------------------------------------------------------------------J,05 «»«.,r,E»s N0TE: |GROUND| f V—j I 30U ♦ X-AXIS ~ ARROWS ON POTENTIOMETERS INDICATE
I GAIN----- I A V’210 CLOCKWISE ROTATION.
-J— ■=" [VERNIER 2I Q ^7 VR.105-30
—^2---------(,_____________ F 3 T M 2 6 8 9 A- 31
Figure 32. Oscilloscope I-2Jf5-A, completes schematic diagram.
835265-49 (Face p. 42)
Section X. REPAIRS
44. Servicing
Be careful in maintaining and servicing this equipment. Servicing and repair other than the replacement of tubes should be performed only by competent personnel supplied with adequate tools and instruments. An inexperienced operator attempting to locate and repair troubles may damage the equipment to such an extent that shipment to field or base maintenance personnel for repair is necessary.
45. General Repair
Removal and replacement of defective parts or circuit elements in this equipment are difficult in some cases; therefore, take care to avoid further damage to the equipment or to the part being replaced. Before attempting repairs, obtain the proper tools for the job.
a. Identification of Leads. Often it may be necessary to remove other circuit elements to gain access to the defective part. To insure proper reinstallation, make a record of the connections to each removed element and of the position of the element in the equipment.
b. Electrical Connections. When replacing leads, clip them as short as possible for satisfactory connections and avoid using more solder than necessary to make a secure connection. Some clearances are very small; therefore be careful when soldering. A very slight amount of excess solder dropped accidentally inside the equipment may cause other circuits or circuit elements to be short-circuited. Do not heat the lug or connection more than is absolutely necessary, because of possible damage to near-by elements such as chokes, capacitors, resistors, and wiring. When a wire is connected to a tube socket, the connecting wire should be long enough to prevent pull on the socket. Save time and trouble by making a thorough electrical check of any part that appears to be defective before removing it from the equipment.
Caution: Never change the location of parts or wiring leads, particularly in the video amplifier circuit, Such a change may affect the performance of the entire circuit. Never change the length of wiring leads.
46. Mechanical Repairs
a. General. When replacing mechanical parts in the equipment, be careful in disassembling and reassembling any mechanical units. Use screwdrivers and other tools that fit the job at hand. Secure bolts and screws snugly but do not overtighten them.
b. Removing Cathode-Ray Tube.
Caution: Be careful when working around, removing, or replacing the cathode-ray tube. Do not strike the tube or allow strains to be placed on it. The tube is highly evacuated, and injury from flying glass may result if it is broken.
(1) Remove the two screws at the back of the instrument that hold the chassis in the cabinet (fig. 3) and remove the chassis.
(2) Remove from their sockets the two Tubes JAN—6V6GT (V204 and V208) located above the cathode-ray tube socket (fig. 28).
(3) Loosen the clamp (attached to the rear of the tube shield) on the base of the cathode-ray tube.
(4) Loosen the damping ring around the collar on the front part of the tube. Slide the clamping ring back off the collar onto the cathode-ray tube. Proceed carefully in order not to damage any parts.
(5) Remove the collar from the front panel.
(6) Carefully remove the cathode-ray tube from its socket by gently pulling on the base of the tube or by pressing on the alinement key on the bottom of the base.
(7) When the tube has'been pulled out far enough, disconnect the intensifier clip from the terminal on the side of the cathode-ray tube. The tube then can be removed completely through the front panel.
(8) To remove the tube shield from the chassis, unscrew the two mounting screws that fasten it to the top framework. In replacing the cathode-ray tube, the clamping ring must be placed over the base of the tube as it is being inserted into the shield. The tube is then mounted in the reverse of the procedure outlined above.
43
Section XI. ALINEMENT AND ADJUSTMENT
47. Voltage-Regulator Adjustment
The voltage regulator must be readjusted whenever tubes are changed in the voltage-regulator circuit. The procedure is as follows:
a. Remove the chassis from the cabinet and connect the power cord to an a-c power source of the correct value.
5. Turn the BEAM switch OFF and the POWER switch ON.
Caution: Be careful when working on the inside of the chassis with the voltage on. Dangerously high voltages are present. Avoid especially the high-voltage rectifier, V214, and the cathode-ray tube socket and circuits.
c. Hold interlock switch S208 (fig. 25) closed manually; after about 30 seconds, measure the voltage between pin 8 on tube V211 (fig. 31) and the chassis with a d-c voltmeter.
d. If the voltage is not 155 volts, adjust the voltage-regulator adjustment on the bottom of the chassis (R254, fig. 31) until a reading of 155 volts is obtained.
48. Adjustment of Frequency-Compensation Coils and Attenuator Circuit
Note. These circuits are adjusted at the factory. They should be readjusted only when it is certain that they are out of alinement and are causing distortion of signal waves.
a. Remove the chassis from the case and short out interlock switch S208 with a short wire j umper.
1). Start up the oscilloscope (par. 11).
c. Connect a good square-wave signal of about 10,000 cps repetition frequency or higher and ap
proximately 100 volts peak-to-peak amplitude to the Y-SIGNAL INPUT terminal.
d. Set the attenuator switch at INPUT UNDER 250 V. RMS.
e. Adjust the frequency controls to obtain two or three cycles of the signal on the screen.
f. Adjust the coils and the attenuator capacitor in the following order for least distortion of the square wave on the screen: C202, L204, L203, L202, and L201 (figs. 28, 29, and 31).
g. Repeat the adjustment of the capacitor and all the coils in the same order as before.
h. Turn up the intensity until the return trace is visible on the screen. If this is impossible, open the blanking switch S204 on the rear panel of the oscilloscope (fig. 3).
i. Adjust coils L206 and L205 (fig. 28) for least distortion at the end of the pattern where the return trace starts.
j. Remove the signal and shut off the power. Be sure to remove the jumper from the interlock switch before putting the chassis back in the case.
49. Unsatisfactory Equipment Report
a. WD AGO Form 468 (Unsatisfactory Equipment Report) for Equipment Used by the Army. WD AGO Form 468 will be filled out and forwarded through channels to the Office of the Chief Signal Officer, Washington 25, D. C., when trouble occurs more often than is normal, as determined by qualified repair personnel.
b. AAF Form 54 (Unsatisfactory Report) for Equipment Used by the Air Force. AAF Form 54 will be filled out and forwarded to Commanding General, Air Materiel Command, Wright-Patterson Air Force Base, Dayton. Ohio, in accordance with AAF Regulations 15-54.
44
APPENDIX I
REFERENCES
Xote. For availability of items listed, check FM 21-6 and Department of the Army Supply Catalog SIG 1. Also see latest issue of FM 21-6 for applicable technical bulletins, supply bulletins, modification work orders, and changes.
1. Army Regulations
AR 330-5, Safeguarding Military Information.
2. Supply Publications
SIG 1, Introduction and Index.
SIG 7-I-245-A, Organizational Spare Parts.
SIG 8-I-245-A, Higher Echelon Spare Parts.
SB 11-76, Electron Tube Supply and Reference Data.
SB 11-76, Signal Corps Kit and Materials for Moisture- and Fungi - Resistant Treatment.
3. Technical Manuals on Auxiliary Equipment and Test Equipment
TAI 11-1200, Radar Test Equipment Application, Description, and Performance Characteristics.
4. Packaging Specifications
a. Joint Army-Navy Packaging Specifications.
JAN-P-100, General Specifications.
JAN-P-116, Preservation, Methods of.
b. U. S. Army Specification.
100-2E, Marking Shipments by Contractors (and Signal Corps Supplement thereto).
c. Signal Corps Instructions.
726-15, Interior marking.
5. Other Publications
FM 21-6, List and Index of Department of the Army Publications.
TB SIG 13, Moistureproofing and Fungiproofing Signal Corps Equipment.
TB SIG 66, Winter Maintenance of Signal Equipment.
TB SIG 72, Tropical Maintenance of Ground Signal Equipment.
TB SIG 75, Desert Maintenance of Ground Signal Equipment.
TB SIG 123, Preventive Maintenance Practices for Ground Signal Equipment.
6. Forms
WD AGO Form 468 (Unsatisfactory Equipment Report).
AAF Form 54 (Unsatisfactory Report).
45
APPENDIX II
REFERENCE TABLE OF PARTS
1. Supply Catalog Pamphlets Signal Portion of the Department of the Army
For an index of available supply catalogs in the Supply Catalog, see the latest issue of SIG 1.
2. Reference Table of Parts for Oscilloscope 1-245-A *
Ref. symbol Name of part and description Function of part
C-224 CAPACITOR, fixed: mica; 25 mmf±10%; 500 vdcw. Charging capacitor (sweep), V205.
C-237 CAPACITOR, fixed: mica; 51mmf±5%; 2,500 vdcw. Differentiator, CRT blanking.
C-223 CAPACITOR, fixed: mica; 125 mmf±10%; 500 vdcw. Charging capacitor (sweep), V205.
C—203 CAPACITOR, fixed: mica: 200 mmf±10%; 500 vdcw. Y-signal attenuator, V201A.
C-222 CAPACITOR, fixed: mica; 600 mmf± 10%; 500 vdcw. Charging capacitor (sweep), V205.
C-221 CAPACITOR, fixed: mica; 2,500 mmf±10%; 500 vdcw. Charging capacitor (sweep), V205.
C-209, C-241 CAPACITOR, fixed: mica; 5,000 mmf±20%; 300 vdcw. C-209: Cathode bypass, V202A. C-241: Coupler (V207).
0-220-z ■_ CAPACITOR, fixed: paper; 10.000 mmf± 10%; 400 vdcw. Charging capacitor (sweep), V205.
C-236 CAPACITOR, fixed: paper; 10,000 mmf±20%; 1,500 vdcw. CRT grid coupler.
O-129_ CAPACITOR, fixed: paper; 40,000 mmf± 10%; 400 vdcw. Charging capacitor (sweep), V205.
0-213, C-215, C-238_ CAPACITOR, fixed: paper; 100,000 mmf± 20%; 600 vdcw. C-213: TEST SIGNAL voltage divider. C-215: EXTERNAL SYNC SIGNAL coupler. C-238: CRT control grid bias-voltage filter.
0-235 CAPACITOR, fixed: paper; 100,000 mnif± 20%; 1,000 vdcw. CRT focusing voltage filter.
C-218 CAPACITOR, fixed: paper; 200,000 mmf± 10%; 400 vdcw. Charging capacitor (sweep), V205.
C-214 . CAPACITOR, fixed: paper; 250,000 mmf± 20%; 600 vdcw. X-signal input coupler, V206A.
C-211. C-212, C- CAPACITOR, fixed: paper; 500,000 mmf± C-211: High frequency compensation, V203.
226, C-227. 20%; 400 vdcw. C-212: High frequency compensation, V204. C-226: High frequency compensation, V207. C-227: High frequency compensation, V208.
0-231, C-234 CAPACITOR, fixed: paper; 500,000 mmf + C-231: Filter, — 280-volt supply.
20%; 600 vdcw. C-234: Filter, + 280-volt supply.
C-239, C-240 CAPACITOR, fixed: paper; 500,000 mmf+ 20%-10%; 1,500 vdcw. Filters, — 1,080-volt supply.
C-217 CAPACITOR, fixed: paper; 1 mf±10%; 400 vdcw. Charging capacitor (sweep), V205.
46
Ref. symbol
Name of part and description
Function of part
C-206, C-228, C-229.
C-201—1____________
C-205, C-225_ _ .. _
C-230______________
C-233______________
C-216___________+ _
C-204______________
C-207, C-208_______
C-232___..i________
C-202______________
L-203, L-204_______
L-207, L-208_______
L-201, L-202_______
L-205, L-206 _
F-201______________
[-201______________
R-210, R-217_______
R-221, R-244______
R-236______________
R-213, R-214, R-255.
R-232, R-235_______
R-211, R-212_______
R-218, R-220, R-■245, R-249.
CAPACITOR, fixed: vdcw.
paper; 1 mf±20%; 400
CAPACITOR, fixed: paper; 1 mf±20%; 600 vdcw.
CAPACITOR, fixed: paper; 8 mf±20%; 400 vdcw.
CAPACITOR, fixed: dry electrolytic: 16 mf + 40%-10%; 450 vdcw.
CAPACITOR, fixed: electrolytic; 16 mf+50% -10%; 475 vdcw.
CAPACITOR, fixed: dry electrolytic; 24 mf + 40% -10%; 150 vdcw.
CAPACITOR, fixed: dry electrolytic; 24 mf + 40% -10%; 350 vdcw.
CAPACITOR, fixed: dry electrolytic; 2 sect: 30 30 mf +40% -10%; 450 vdcw.
CAPACITOR, fixed: dry electrolytic; 40 mf + 50% -10%; 450 vdcw.
CAPACITOR, variable: mica dielectric; 6.5-35 mmf; 400 v RMS test.
COIL, RF: choke; 3-pie winding; unshielded;
7.5-15 mh; 100 ma; 142 ohms DC.
COIL, AF: filter; 18hy±10%; 43 ma; 350 ohms DC.
COIL, RF: choke; 3-pie winding; unshielded; 1.81-4.2 mh; 64 ohms DC.
COIL, RF: choke; 4-pie winding; unshielded;
11.3-23.4 mh; 190 ohms DC.
FUSE, cartridge: 1.5 amp, 250 v_______________
LAMP, LM-27: incandescent; 6-8 v; 0.25 amp
RESISTOR, fixed: comp; 240 ohms±5%; w__
RESISTOR, fixed: comp; 390 ohms± 10%; 1 w
RESISTOR, fixed: comp; 1300 ohms± 5%; % w_ _ RESISTOR, fixed: comp; 8200 ohms± 10%; 1 w_
RESISTOR, fixed: comp; 10,000 ohms+10%; % w.
RESISTOR, fixed: comp; 24,000 ohms ± 5%; 1 w
RESISTOR, fixed: ww; 25,000 ohms+10%; 10
w.
R-239----------- RESISTOR, fixed: comp; 33,000 ohms+10%;
2 w.
R-216, R-257____ RESISTOR, fixed: comp; 51,000 ohms±5%; 1 w.
R-264______________
R-204, R-258_______
R-219, R-247 ______
RESISTOR, fixed: comp; 51,000 ohms±5%; 2 w.
RESISTOR, fixed: comp; 100,000 ohms+10%; 1 w.
RESISTOR, fixed: comp; 150,000 ohms+10%; 1 w.
R-202_____________
RESISTOR, fixed: comp; 200,000 ohms±5%; % w.
C-206: Coupler, V201B.
C-228: Regulated-voltage filter.
C-229: Regulator control voltage filter.
Y-signal input coupler, V201A.
C-205: Coupler, V202A.
C-225: Coupler, V206B.
Filter, — 280-volt supply.
Filter, + 280-volt supply.
Cathode bypass, V205.
Cathode voltage-dropping resistor bypass, V201A.
C-207: Low frequency compensation, V202A.
C-208: Low frequency compensation, V202B.
Filter, + 280-volt supply.
Y-signal attenuator, V201 A.
L-203: High frequency compensation, V203.
L-204: High frequency compensation, V204.
Filter choices, + 280-volt supply.
L-201: High frequency compensation, V202B.
L-202: High frequency compensation, V202B.
L-205: High frequency compensation, V207.
L-206: High frequency compensation, V208.
A-c power fuse.
Pilot light.
R-210: Cathode bias resistor, V202A.
R-217: Cathode bias voltage divider, V202B.
R- 221: Cathode bias resistor, V203, V204.
R-244: Cathode bias resistor, V207, V208.
Cathode bias resistor, V205.
R-213: Plate load, V202A.
R-214: Plate load, V202B.
R-255: Plate voltage dropping resistor, V210.
R-232: TEST SIGNAL voltage divider.
R-235: Grid series limiting resistor, V205.
R-211: Low frequency compensation, V202A.
R-212: Low frequency compensation, V202B.
R-218: Plate load, V203.
R-220: Plate load, V203.
R-245: Plate load, V207.
R-249: Plate load, V209.
Cathode bias voltage divider, V205.
R-216: Cathode bias voltage divider, V202B.
R-257: Filter resistor, —280-volt supply.
Filter resistor, — 1080-volt supply.
R-204: Cathode load resistor, V201A.
R-258: CRT grid resistor.
R-219: Screen voltage dropping resistor, V203, V204.
R-247: Screen voltage dropping resistor, V207, V208.
Y-signal attenuator, V201A.
47
Ref. symbol
Name of part and description
Function of part
R-261_____________
R-205, R-240______
R-208, R-242______
R-288, R-229,
R-230, R-231.
RESISTOR, fixed: comp; 200,000 ohms±5%; 1 w.
RESISTOR, fixed: comp; 240,000 ohms±5%; 1 w.
RESISTOR, fixed: comp; 300,000 ohms±5%; 1 w.
RESISTOR, fixed: comp; 470,000 ohms±10%;
% w.
R-256______________
R-222, R-223, R-
237, R-246, R-248.
RESISTOR, fixed: comp; 510,000 ohms±5%; 1 w.
RESISTOR, fixed: comp; 750,000 ohms±5%; 1 w.
R-209, R-215,R-259_
RESISTOR, fixed: comp; 1 meg±10%; /2 w_
R-263______________
R-201, R-203_______
R-233______________
R-224, R-225, R-226, R-227, R.-250, R-251, R-252, R-253.
R-207, R-243_______
R-234, R-260_______
RESISTOR, fixed: comp; 1 meg+10%; 1 w_
RESISTOR, fixed: comp; 1.8 meg±10%; % w__
RESISTOR, fixed: comp; 4.7 meg±10%; % w__
RESISTOR, fixed: comp; 4.7 meg±10%; 1 w__
RESISTOR, variable: comp; 15,000 ohms; J4 w; 3 term.
RESISTOR, variable: comp; 100,000 ohms; % w; 3 term.
R-206___________— ~
R-241, R-262____
R-254_____________
R-238_____________
S-208_____________
S-202_____________
S-204_____________
S-201_____________
S-203_____________
S-207_____________
S-206_____________
S-205_____________
T-201_____________
V-210_____________
V-215_____________
V-214_____________
V-213_____________
V-209_____________
RESISTOR, variable: 100,000 ohms; % w; 3 term.
RESISTOR, variable: comp; 500,000 ohms; % w; 3 term.
RESISTOR, variable: comp; 1 meg; % w; 3 term.
RESISTOR, variable: comp; 4 meg; % w; 3 term.
SWITCH, push: momentary; SPST; single sect.. SWITCH, rotary: 1 pole, 3 position; single sect. SWITCH, rotary: SPST; single sect__________
SWITCH, rotary: SPDT; single sect__________
SWITCH, rotary: 2 pole, 9 position; 2 sect_
SWITCH, toggle: SPST; single sect__________
SWITCH, toggle: DPDT; single sect__________
SWITCH, toggle: SPDT; single sect----------
TRANSFORMER, power: plate and filament_____
TUBE, electron: JAN-VR105/30_______________
TUBE, electron: JAN-5CP1-------------------
TUBE, electron: JAN-5R4GY__________________
TUBE, electron: JAN-5Y3GT__________________
TUBE, electron: JAN-6SJ7----- -----------
CRT voltage divider.
R-205: Cathode voltage dropping resistor, V201A.
R-240: Cathode load resistor, V206A.
R-208: Cathode load resistor, V201B.
R-242: Cathode load resistor, V206B.
Decoupling resistors for direct connection to CRT deflecting plates as follows: R-228 for X2, R-229 for XI, R-230 for Y2 and R-231 for Yl.
Cathode bias resistor, V211.
R-222: High frequency compensation, V203.
R-223: High frequency compensation, V204.
R-237: Series resistor for charge of sweep capacitor, plate V205.
R-246: High frequency compensation, V207.
R-248: High frequency compensation, V208.
R-209: Grid resistor, V201B.
R-215: Grid resistor, V202B.
R-259: CRT cathode resistor.
CRT voltage divider.
R-201: Y-signal attenuator, V201A.
R-203: Grid resistor, V201A.
Grid resistor, V206A, for X-axis signal input.
R-224, R-225: Voltage divider, V203.
R-226, R-227: Voltage divider, V204.
R-250, R-251: Voltage divider, V207.
R-252, R-253: Voltage divider, V208.
R-207: Y-position control, V201B.
R-243: X-position control, V206.
R-234: SYNC SIGNAL AMPLITUDE control.
R-260: INTENSITY control for CRT.
Y-GAIN control, V202A
R-241: X-GAIN control, V206B.
R-262: FOCUS control for CRT
Voltage regulator adjustmentj V209.
FINE FREQUENCY control, V205.
Power interlock switch.
SYNC SIGNAL SELECTOR switch, V205.
Blanking switch.
Y-GAIN attenuator switch, V201A.
COARSE FREQUENCY switch, V205.
POWER ON switch.
Line voltage (115v or 230v) selector switch.
BEAM ON switch, controls CRT cathode voltage.
Power transformer.
Voltage regulator tube.
Cathode-ray tube.
Rectifier, — 1080-volt supply.
Rectifier, ± 280-volt supply.
Voltage regulator control tube.
48
Ref. symbol
Name of part and description
Function of part
V-201, V-202, V-206-
V-203, V-204,
V-207, V-208,
V-211.
TUBE, electron: JAN-6SN7GT________
TUBE, electron: JAN-6V6GT/G; JAN-1 A_
V-212.
V—205.
TUBE, electron: JAN-6X5GT___________________________
TUBE, electron: JAN-884_____________________________
V-201, V-202: Y-axis video amplifiers.
V-206: X-axis amplifier.
V-203, V-204: Y-axis paraphase amplifiers.
V-207, V-208: X-axis paraphase amplifiers.
V-211: Voltage regulator variable resistance tube.
Rectifier, — 280-volt supply.
Saw-tooth generator.
U.S GOVERNMENT PRIMING OFFICE: IS4S
49
f
UNT LIBRARIES DENTON TX 76203
l■lllllllllllllllllllllllllllllllll
1001729027