ing voltage is fed back to each cathode in such multivibrator, while the pentode plate serves
a manner that the currents remainunchanged. to electron-couple the multivibrator to the
output circuit. During the negative - going
The 3rd stage, Switched Amplifiers V503A portion of the output waveform, tube conduc-
and B, provides 15 db gain and also serves tion discharges stray capacities rapidly and
as a switch that can be turned off and on rap- affords a comparatively fast decay time. To
idly during ALTERNATE and CHOPPED op- improve waveform rise-time when the tube
eration. The plate circuits of the switched goes out of conduction, CR1 clamps aportion
amplifiers are frequency compensated to ex- of the plate load to the +13O-volt buss during
tend the upper frequency limit to above 10 the positive-going half of the wave. This ef-
megacycles. fectively reduces the resistance throughwhich
stray capacities must charge, thus reducing
The plate circuits of the Switched Amplifiers rise time, while retaining a high plate-load
in one channel are connected to the output of resistance to limit tube conduction during the
the other channel, without attenuation. No negative-going half of the waveform.
mixing of signals takes place since the am-
plifier s cannot be operated simultaneously;
3-1 1 REGULATED LOW-VOLTAGE POWER
the Ifoff" channel always appears as an open SUPPLY
circuit to the "onff channel.
The Dual Channel Amplifier also contains The complete low-voltage power supply shown
circuits for switching the two channels off in figure 3-4 provides five regulated and one
and on during CHOPPED and ALTERNATE unregulated voltages as follows: regulated ,
operation. -150 Volts, -82 Volts, t130 volts, t260 volts
and t400 volts; unregulated, +415 volts.
For CHOPPED operation, the Switching Mul-
tivibrator free -runs at approximately 100 Each regulated voltage supply except the -82
kilocycles, switching each of the channels volt has its own transformer winding and
off and on at this rate. During CHOPPED op- rectifier. The -150-volt supply contains the
eration afast negative pulse is takenfrom the reference voltage for all other regulated sup-
Switching Multivibrator and applied through plies and is thus the only independent one.
V504B to the CRT intensity grid so that the The unregulated outputs from the rectifiers
chopping lines between the two traces will be which supply the three positive-voltage sup-
blanked out. plies are stackedin series. The higher-volt-
age regulated supplies tap in at higher volt-
For ALTERNATE operation, a high negative ages on this stack. The totalcurrent require-
bias converts the free-running multivibrator ment of the three positive-voltage regulated
to a bistable flip-flop. supplies must flow through the lowest recti-
fier in the stack, which is sufficient for d-c
A signal obtained from the Sweep Generator heater current to a series string of electron-
at the end of each sweep switches the Multi- tubes. Thus the negative return of the lowest
vibrator from one state to the other, thus stacked supply is returned to ground through
alternately turning on one channel for one the tube heaters as a load with the total heater
sweep, the other channel for the next. voltage held constant bya shunt voltage regu-
lator. The shunt regulator, V49 and V50,
absorbs slight differences in the 150A's in-
stantaneous current requirements and input
3-10 CALIBRATOR variations such that the voltage applied to the
d-c heater string is constant.
The calibrator circuit is aplate-coupled mul-
tivibrator which is made to free run at ap- The operation of the four regulated-voltage
proximately 1000 cps, the rate being primar- supplies is identical so only the -150v supply
ily determined by C116, R292 and C117, R285. is described. V44, V45 and V46 are the
The 100-volt square-wave output is positive- regulator tubes which act as variable resis-
going with the base line clamped to ground tors controlled by the voltages at the control
by crystal diode CR2. The output voltage is and screen grids of Control Tube V47. If the
selected from a voltage divider composed of regulated output voltage from the cathode of
R289, R290, R291 and the attenuator in the the Series Regulators tends to increase ,
CALIBRATOR selector switch. The output the voltage at the grid of V47 tends to in-
half of the multivibrator tube, V32, is a pent- crease, causing V47 to draw more current.
ode whose screen serves as the plate for the This lowers the plate voltage of V47 and con-
3-11 |
ACEC
HEWLETT-PACKARD
