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TM 11-5820-498-35
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.
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
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
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-

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