Figure 2-18. Negative regulated power supply, simplified schematic diagram.

TM 11-6660-204-25

Figure 2-18. Negative regulated power supply, simplified schematic diagram.

ground. The voltage of potentiometer R412 is ap-

supplied from positive voltage reference tube

plied to the control grid of positive control ampli-

V404. Because the cathode voltage is held con-

fier tube V403. The screen-grid voltage for tube

stant, only the grid voltage affects operation of

V403 is obtained from a voltage divider consisting

this circuit. The grid voltage is supplied from a

of resistors R408 and R409 and positive voltage

bleeder network across the regulated positive

references tube V404 connected across the posi-

300-volt output determined by the position of the

tive 300-volt output. The plate of tube V403 is

wiper arm of potentiometer R412. When an in-

directly connected to the grid of tube V402

crease of voltage occurs at the cathode of tube

through resistor R407, and determines the grid

V402 as a result of an increase in line voltage or a

decrease in load current, the voltage across the

bias on this series regulator tube. Positive voltage

bleeder increases. A portion of this voltage, deter-

reference tube V404 is a cold cathode-type gas

mined by the setting of potentiometer R412, is

voltage regulator tube, normally operating at 87

amplified by tube V403 and applied as a negative

volts. This tube is connected to the cathode of tube

swinging grid voltage to tube V402. This decrease

V403 to provide a constant reference voltage for

in grid voltage causes an increase in the effective

comparison with the grid voltage of control ampli-

plate to cathode resistance and increases the volt-

fier tube V403.

age drop across tube V402. This increase in volt-

(2) Series regulator tube V402 functions as a

age drop, returns the grid of tube V403 almost to

variable resistor, the resistance is controlled by

its original bias. The action of the regulator is

its grid voltage. A more positive grid voltage de-

very rapid and may be considered instantaneous.

creases resistance and a less positive voltage in-

Capacitors C404 and C405 with resistor R410

creases resistance. Control amplifier tube V403

form a series circuit across the output of the reg-

controls the amount of voltage supplies to the grid

ulated positive 300-volt supply for any rapid

of tube V402. The cathode of tube V403 is con-

changing voltage or for ripple voltage. The capac-

nected to a constant reference voltage, which is

2-21