Power Supply Circuits-continued

TM 11-5820-509-35

applied as a 150-volt dc plate and screen voltage to rf

front of RT-671/PRC-47 (or a remote control on-off

amplifiers V1 and V2 of signal data translator A3.

switch) is placed to ON. Push-to-talk relay A5K 1 in the

power supply module is operated by any one of the

d. When a 26.5-volt dc primary source is used for

following conditions provided that overtemperature

operation of the radio set, this source is connected to

cutout K103 in the power amplifier compartment has not

the POWER receptacle on the front of RT-671 /PRC-47

opened: by CW-FSK/VOICE switch S2 (when placed to

instead of the 115-volt ac power cable. The 26.5-volt

the CW-FSK position by OPR-TUNE switch S102 (when

incoming power is routed through fuse F1 and the

placed to the TUNE position); and by the handset ptt

contacts of dc power control relay K 1 to the power

switch (when it is pressed). Thermal override switch

supply circuits of the radio set. With no ac power

S3B is physically part of BATTERY TEST switch S3A,

connected, dc power control relay K1 is operated when

and it must be held fully depressed to permit operation

the POWER-LIGHTS switch (S1) on the front panel of

of the radio set after overtemperature cutout K103 has

RT-671/PRC-4? (or a remote control on-off switch) is

operated.

placed to ON. As this relay operates, the contacts in the

c. In the transmit mode, ac power control relay K2

115-volt ac circuit are opened, and the contacts

associated with the 26.5-volt circuit are closed so that

and B + relay K3 in the main chassis of the radio set,

power is applied to: the 26.5-volt dc circuits of audio

and push-to-talk relay A5K1 are all operated. The 115-

frequency amplifier A1, signal data translator A3, and

volt ac primary power is routed through the contacts of

the panel lamp circuits on the front of RT-671/PRC47;

K2 and A5K1 to the 115-volt primary winding of high-

the filter consisting of inductor L1 and capacitors C25

voltage transformer T1. This primary winding is tapped

and C26 to the normally-closed contacts of B + relay K3

for operation with the power oscillator described in

to the 24-volt dc circuits of audio frequency amplifier

paragraph 2-8 e. High-voltage transformer T1 contains

A1; through the normally-closed contacts of B + relay K3

several secondary windings that provide a variety of ac

to the 24-volt dc circuits of signal data translator A3; and

and dc outputs during transmitter operation. A 6.3-volt

to voltage regulator Q1 through Q3. The push-to-talk

ac winding provides heater power for the power

relay in the power supply is armed so that it may be

amplifier stage and for the rf amplifiers and the driver in

operated by selection of the transmit mode, and

signal data translator A3. An additional secondary

regulated dc is routed from the output of the voltage

winding is provided for each of the four rectifier-filter

regulator to the 20-volt circuits of the radio set and

circuits that supply dc potentials to other parts of the

through the contacts of B + relay K3 to the circuits of

transmitter.

Rectifier CR1 through CR4 and its

amplifier-modulator A2 and signal data translator A3

associated filter and bias adjusting network provide-110

that are voice-operated.

volts dc and-32 volts dc for the grid circuits of the power

amplifier (V101) and the driver (A3V3) respectively.

e. Push-to-talk relay K1 in power supply A5 is

Each of these outputs is individually adjustable to

operated by selection of the transmit mode. (Refer to

provide optimum operation of the vacuum tube with

paragraph 2-8 b for a detailed discussion of operation of

which it is associated. Rectifier CR6 through CR17 is a

relay K1.) In addition to a contact-pair in the 115-volt ac

fullwave bridge-type circuit employing three diodes in

circuit to high-voltage transformer T1, another contact-

each leg. The output of this rectifier is filtered by

pair is associated with the center-tap of this primary

capacitor C6 and resistors R6 and R7 to provide 1500

winding. As these contacts close, dc power is applied to

volts dc for the plate circuit of power amplifier V101.

400-Hz power oscillator Q1-Q2, and a 26.5-volt, 400-Hz

Rectifier CR18 through CR21 provides an output that is

squarewave ac is generated and applied to part of the

filtered by capacitors C19 and resistors R9 and R10 and

transformer primary winding. With this square wave

it operates the screen circuit of the power amplifier tube.

voltage applied, operation of the transformer, rectifier,

The rectified output of CR22 through CR25 is routed to

and filter circuits is identical to the description shown in

the filter circuit consisting of capacitor C20 and resistors

paragraph 2-8 c except that a contact-pair on ac power

R11 and R12. The output of this circuit is applied to the

control relay K1 selects a tap on the 6.3volt ac filament

driver stage (V3) of signal data translator A3 and a

winding of T1 for proper output to the connected

portion of it is dropped through resistor R8 before being

vacuum tube filament circuits.

2-13