Low Voltage Supply

TM 11-6625-537-14-1

applied to the base of Q2. A positive going signal

trolled by ON switch S1 and protected by a fuse.

on the base of Q2 will cause the internal resistance

A 1.5-ampere fuse is used for 115-volt operation,

of Q2 and Q3 to increase. When the output

and a 0.25-ampere fuse is used for 230-volt

voltage is higher than normal, Q1 will become

operation.

forward biased causing the voltage drop across

c. Positive 200- and 150-Volt Supply. Positive

Q3 to increase and restore the voltage to normal.

00 and 150 volts for the dc vtvm is obtained from

The regulated output voltage is between 5.6 and

a 190-volt secondary winding. The ac voltage is

6.1 volts and will vary no more than 0.020 volt for

half-wave rectified by CR201 and filtered by

an input voltage change of 102 to 128 volts.

R228, R229, C214A, and C214B, Positive 200

volts for V203B is obtained directly from the

e. Unregulated Filament Supply. There are

three unregulated filament supplies. A 6.3-volt

anode of CR201, Positive 150 volts for V202 and

secondary winding provides filament voltage to

V203A is obtained from the plate of regulator

V202, V203 and chopper CK1 in the dc vtvm. A 5-

V204.

v o l t secondary winding is used to light the

d . Reguluted Filament Supply. An 18-volt

d e c i m a l indicator lamp (PL1 through PL4)

c e n t e r tapped winding is used to provide a

selected by level A or RANGE switch S2. A

regulated 5.9-volt dc supply for the filaments of

second 6.3-volt winding (not shown in figure 5-6)

V501 and V502 in the ac-to-dc converter, and for

provides filament voltage for V101 and V105 in

V104 in the 500-volt dc reference supply. The ac

voltage is full-wave rectified by CR103 and CR104

the 500-volt dc reference supply. The filaments of

these tubes are operated at approximately 400

and filtered by C103. Transistor Q3 senses the

volts dc potential to prevent internal high-voltage

difference between the dc output voltage and a

breakdown.

reference voltage obtained from V102 in the 500.

volt dc reference supply, The output of Q1 is

5-11