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GENERAL RADIO COMPANY
will go on to produce a negative pulse. DC connections through-
out cause the entire system to be bistable
With the pulse amplitude switch s e t for a maximum, output
tubes V507 and V508 conduct about 160 ma of plate current.
Voltage produced by this current in R548 through R557 consti-
tutes the output pulse. Negative pulses are, for example, pro-
duced when the plate current of V508 is turned on in R548 (50
ohms) to produce -7.5 volts with respect to ground (J507) behind
50 ohms. S501 controls output impedance, and consequently
output voltage. Note that the link between 3507 and J508 can be
opened to insert a battery or dc power supply to translate the dc
component of the pulse away from ground.
When V507 and V508 are conducting with full screen volt-
age (maximum pulse amplitude), about 100 ma of the current in
the "onn output tube flows through the *on" driver tube. Under
"normaln conditions there will be 160 ma in V507 and 100 ma in
V506. The additional 60 ma flows in R537.
If pulse amplitude i s decreased, means must be provided
for maintaining plate voltage on the driver tubes (normally main-
tained by conduction of the output tubes). Therefore, a s the
PULSE AMPLITUDE switch setting is decreased, resistors R567
through R575 are switched in from ground to cathodes of V507
and V508, reducing screen voltages and thereby maintaining
plate voltages.
Pulse amplitude i s reduced by reduction of the screen
voltage of the output stage. The screenresistance (R558 through
R566) for V507 and V508 is increased to decrease screen volt-
age. The pulse current is stabilized against line variations and
transients by V511, which controls the screen voltage supplied
to the amplitude control network. V511 is essentially a cathode
follower, whose grid voltage is supplied by the network consist-
ing of R578, R579, V512, V513, and V514 with this network be-
tween +300volts regulatedand -550 volts. Suppose, for example,
that the line voltage decreases. The -200 volt supply feeding
the cathodes of V507 and V508 becomes l e s s negative and the
screen voltage on these stages tends to decrease, decreasing
plate current. Actually the -550-volt supply becomes l e s s nega-
tive by an amount which, when referred to the cathode of V511,
exactly equals the change in cathode voltage on V507 and V508.
Thus the plate current a t these stages tends to remain constant,
and i s , in fact, affected only by changes in heater voltage.
4.8 POWER SUPPLIES.
4.8.1 GENERAL. All necessary power supplies are in the Type
1391-P2 Power Supply Unit. This supply provides the four
6.3-volt heater supplies and the nine d-c power supplies required.
One 10-conductor cable carries the four heater palrs and the
115-volt conductors required to operate the blower. The four
heaters are identified by the letters P for positive, A for am-
plitude comparator, G for ground, and N for negative. The A bus
is
a shielded, low-noise winding that provides heater voltage for
the various amplitude comparators of the input, delay, sweep,
and pulse-timing circuits. The ground bus is a heater winding at
ground potential for tubes whose cathodes are close to ground,
and the N bus supplies those tubes whose heaters normally run
a t 150 to 200 volts negative. The heater connection of each
tube i s identified by the key letter printed on the heater termi-
nals of that tube in the circuit diagrams, Figures 5.1 through 5.6.
4.8.2 PLATE SUPPLIES.
4.8.2.1
General. All supplies use
silicon rectifier circuits.
Those providing appreciable power are full-wave doublers, while
the low-drain bias supplies are half-wave rectifiers. The plate
supplies, in the order shown from top to bottom of the elemen-
tary diagram on the back of Figure 5.6, are:
a. a 110-volt 200-ma doubler supply added to a 300-volt
doubler supply to produce f410 volts unregulated. This supply
provides plate voltage for the +300-volt regulator.
b. a second 300-volt doubler providing +I40 volts for V503
andV504 in the pulse-generating section and +55 and -150volts
for the bistable gate circuits.
c. a -200-volt doubler for the pulse output stage.
d. a half-wave rectifier supplying additional 340-v bias to
V509 for the pulse output stage and pulse amplitude regulator.
4.8.2.2
Regulator. A Type 6AS6 series tube (V6Ol) is biased
to the proper operating point to produce a 300-volt output by
means of the plate current of V602 flowing through R605. The
level of this plate current i s controlled by the grid voltage on
V602, controlled by R612. R612 therefore determines the regu-
lated output voltage. The 150-volt reference voltage for the cath-
ode of V602 is produced by V603. Some unregulated voltage from
the 410-volt supply is developed across R607 and
is
added to the
grid network of V602. This provides compensation for changing
input voltage. When the output voltage tends to rise due to an
increase in line voltage, rhe grid voltage on VG02 increases, in-
creasing the bias 0nV6Ol and lowering the output voltage. This
compensation produces a negative slope of output voltage with
increasing line voltage over the range from 100 to 130 volts.
From 105 to 125 volts, the output voltage from the supply changes
by l e s s than one-half volt.
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