Section III. AMPLIFIER-POWER SUPPLY GROUP OA-3633(*)/GRC, CIRCUIT FUNCTIONING

TM 11-5820-498-35

Section Ill. AMPLIFIER-POWER SUPPLY GROUP

OA-3633(*)/GRC, CIRCUIT FUNCTIONING

the operating frequency of the receiver-transmit-

2-9. Amplifier-Power Supply AM-2060(*) /

ter. Switch S2 is set to a position that includes

GRC, Block Diagram

the receiver-transmitter operating frequency.

(fig. 2-1)

c. Audio Amplifiers Q1 and Q2. The audio out-

The AM-2060(*)/GRC is the main component of

put of the receiver-transmitter is applied to audio

the OA-3633(*)/GRC; the other component is

amplifiers Q1 and Q2.

Cable Assembly, Special Purpose, Electrical

(1) Remote audio output. Amplifiers Q1 and

CX-4656/GRC (para 2-11, fig. 3-5). The

Q2 amplify the audio signals applied to it from

CX-4656/GRC provides dc power and audio sig-

the receiver-transmitter and provide two outputs,

nal connection between the receiver-transmitter

muted and unmuted. The output signals are ap-

and the AM-2060 (*)/GRC. The

plied to crewmember control boxes when they are

AM-2060(*)/GRC converts vehicular battery

part of the system.

power (24 3 volts dc) to the operating voltages

(2) Local audio output. The amplifier audio

for the receiver-transmitter (a below), and am-

signals from Q1 and Q2 are also applied through

plification of the receiver-transmitter received

SPKR switch S1 to receive-transmit relay K1.

audio signals for application to the loudspeaker

When the receiver-transmitter is keyed for trans-

in the AM2060(*)/GRC (c(1) below), and to

mission, the keying relay in the receiver-trans-

the crewmember control boxes when they are a

mitter is operated which causes +13 volts dc to

part of the system (c(2) below). The vehicular

be applied to the winding of keying relay K1 in

battery power is also applied to Antenna Match-

the AM-2060(*)/GRC. When K1 operates, it dis-

i n g Unit MX2799/VRC (part of Antenna

connects the audio signal from the loudspeaker,

AT-912/VRC) or to Matching Unit-Base, An-

and thus prevents feedback from the loudspeaker

tenna MX-6707/VRC (part of Antenna

to the audio accessory microphone.

AS-1729/VRRC) (b below).

2-10. AM-2060(*)/GRC, Circuit Functioning

a. Operating Voltages to Receiver-Transmitter.

The nominal 25.5 volts dc from the power source,

a. Audio Amplifiers Q1 and Q2. Q1 and Q2

normally a vehicular battery, is applied through

provide amplification of the audio output signals

from the receiver-transmitter. The amplified

the MT-1029/VRC and PWR circuit breaker CB1

to series regulator Q3 and dc amplifier Q4, volt-

audio output is applied to the AM2060(*)/GRC

age dropping resistor R17, ANT. FREQ. CON-

loudspeaker and to the audio accessories of the

TROL switch S2, and audio amplifiers Q1 and Q2.

associated crewmember control boxes.

(1) Series regulator Q3 and dc amplifier Q4

(1) The audio output signal at pin B of SET

convert and control the applied 25.5 volts dc to a

POWER connector J2 is coupled through imped-

regulated 13 and 3 volts dc. The 13 volts is for

ance matching transformer T1 to the base of

use in the receiver-transmitter where it is con-

push-pull amplifiers Q1 and Q2. The amplified

verted to 10 volts for the transmit and receive

audio output is applied to the primary (terminals

circuits. In the RT-505/PRC-25 only, the 3 volts

1 and 3) of transformer T2. The audio output

dc is used for interval oscillator A10.

across one-half of the secondary of T2 (terminals

(2) Voltage dropping resistor R17 lowers

4 and 5) is coupled through SPKR switch S1

the applied 25.5 volts dc to 2.6 0.3 volts dc.

(ON position) and relay K1 (contacts 8 and 2) to

This voltage is used only in the RT-505/PRC-25

loudspeaker LS1. The audio output across the

as filament voltage for power amplifier V1 when

secondary of T2 (terminals 4 and 6) is applied

the RT-505/PRC-25 is in transmit mode.

t h r o u g h limiting resistor R15 to pin K of

b. Operating V o l t a g e s A p p l i e d t o M X -

POWER INPUT connector J3 to provide a muted

2799/VRC and MX-6707/VRC. The nominal

audio output; and to pin S of J3 to provide an un-

25.5 volts dc is applied through ANT. FREQ.

muted audio output to the crewmember control

CONTROL switch S2 to the MX-2799/VRC or

boxes.

M X - 6 7 0 7 / V R C . The voltage is used by the

(2) A voltage-dividing network, composed

MX-2799/VRC and MX-6707/VRC to control the

of resistors R2 and R3, and temperature-compen-

settings of the matching circuits to provide a

sating thermistor RT1 provide base-to-emitter

close impedance match for the whip antenna at

bias for Q1 and Q2. Thermistor RT1 has a nega-

2-11