Section IV Model 122A/AR
Paragraphs 4-6 to 4-15
currentfor the output stage. The switchingamplifier Either the X1 or the X5 RC networks may be switched
is controlled, in turn, by the switching multivibrator. into the cathode circuit of V101. A Horiz Bal potenti-
ometer and a Phase Adj capacitor are connected be-
4-6. VERTICAL PRESENTATION SWITCH. tween the plates of V101. Tube VlOl feeds another
differential amplifier stage, V102. The output of
4-7. The vertical presentation switch selects the type
of vertical amplifier operation as follows: V102 drives the horizontal deflection plates of the
CRT.
a. A or B. The locked state is used when the
VERT PRESENTATION switch is set to A, B, or B-A. 4-11. SWEEP GENERATOR.
Note that the multivibrator can be locked in either of
4-12. The sweep generator consists of a trigger gen-
its two possible states (Channel A on, or Channel B erator and a sawtooth generator. The trigger generator
on). The other channel (not used) is biased off. In
the B-A position, Channel B is locked on. receives the synchronizing signal selected by the SYNC
selector switch and generates a pulse which initiates
b. ALT. The bistable state is used when the the action of the sawtooth generator. The sawtooth gen-
VERT PRESENTATION switch is set to ALT. Bi- erator then produces one complete cycle. It auto-
stable means stable in either of two positions. For matically shuts itself off by means of feedback upon
example, when operating in the ALT position, Channel completion of one cycle. The sweep circuit will
A is off and Channel B is on until a trigger pulse is operate again when another pulse is received from
received from the sweep. At this moment Channel A the trigger generator, but only after a hold-off time
is turned on and Channel B is turned off. This action duringwhich all of the circuits have had time to return
is repetitive and occurs at the end of each sweep. to their quiescent voltages. This delay is necessary
so that successive waveformswill start from the same
c. CHOP. In the CHOP position the multivibrator voltage each time.
is astable. The circuit is afree-running multivibrator
with approximately a 40 kHz rate.
4- 13'. TRIGGER GENERATOR. The trigger generator
d. B-A. In the B-A (B minus A) position the sig- consists of a synchronizing circuit and a trigger tube,
nal f rom Channel B input is fed directly into the Chan- V201. The synchronizing circuit receives a signal
nel B amplifier. The signal from Channel A input is either from the vertical amplifier for internal syn-
fed into the opposite side of the Channel B differential chronization (+or -), from an internal 6.3-volt source
amplifier. The output of the Channel B amplifier is for line frequency synchronization, or from the hori-
then the difference between the Channel Band Channel zontal input terminals for external synchronization.
A signals. This is the only signal shown on the screen. The trigger generator converts the signal into a fast,
\
4-8. HORIZONTAL AMPLIFICATION SWITCH. constant-amplitude pulse for operation of the start-
stop trigger, V202. Trigger generator, V201, is a
4-9. The horizontal amplifier receives an input signal Schmitt Trigger with narrow hysteresis limits. A
either from the horizontal input terminals or from the negative signal starts the action by causing the trig-
internal sweep generator, amplifies the signal, and ger generator to change state. This action generates
drives the horizontal deflection plates. The horizontal a square wave output. This square wave output is
amplification channel also provides attenuation of the differentiated by L201 into a series of positive and
input signal, magnification of the internal sweep and negative pulses. These pulses are fed to the start-
determines the horizontal position of the trace on the stop trigger.
screen. The signal comes into the input terminals
and is fed to the AC-DC switch. If this switch is in 4- 14. SAWTOOTH GENERATOR. The sawtooth gen-
the AC position the signal goes through a capacitor erator consists of a start-stop trigger, an integrator
which blocks any dc component. If this switch is in switch, an integrator, anda hold-off cathode follower.
the DC position the signal goes straight through. The The pulse from the trigger generator controls the
horizontal input signal passes through the horizontal start-stop trigger which, in turn, controls the inte-
sensitivity section of the SWEEP TIME HORIZ SENS grator switch. The integrator switch controls the
switch. This switch has a three-position frequency- action of the integrator. The integrator generates a
compensated attenuator. linear, rising voltage. This action plus the switching
4- 10. The signal which is fed into the horizontal ampli- action of the integrator switch generates a sawtooth
voltage. This sawtooth voltage is fed to the horizontal
fier may be from either an external source or a saw-
tooth voltage from the sweep generator. The position amplifier and to the hold-off cathode follower. The
output of the hold-off cathode follower is fed to the
of the SWEEP TIME-HORIZ SENS switch will deter-
mine which signal is fed into the amplifier. The gridof the start-stop trigger. This voltage keeps the
amplifier consists of two differential stages in cascade. start-stop trigger from triggering until all the cir-
cuits have had time to recover to their original
Plate-to-grid neutralization is used in both stages.
The input differential amplifier, VlOlA, is driven quiescent voltage.
single-ended. The grid of the undriven tube, VlOlB, 4- 15. GATE CATHODE FOLLOWER. Another func-
connects to the POSITION potentiometer to obtain tion of the sweep generator is to furnish a positive
its bias. Twopotentiometers, HORIZ SENS VERNIER pulse to unblank the cathode-ray tube. This pulse is
and Horiz Gain, in the cathode circuit of VlOl provide obtained from the start-stop trigger. Normally the )
gain adjustment. These potentiometers are in the voltage applied to the grid of the cathode-ray tube cuts
circuit only when the SWEEP TIME-HORIZ SENS off the beam. During the time of the sweep period
switch is in the HORIZ SENS ranges. In the SWEEP a positive pulse is appliedwhich overrides the negative
TIME ranges the SWP EXP switch is used. voltage and unblanks the display.
4-2 00081-2 |
ACEC
HEWLETT-PACKARD
