TM 11-5820-921-40-1
2-19. The necessary operating voltages for circuits in the power amplifier and the system are derived from
a +26.5 Vdc (nominal) primary power source (J3). The +26.5 Vdc is applied directly to the receiver-trans-
mitter which controls the application of power to the system. The +26.5 Vdc is routed to Antenna Coupler
CU-2064/GRC-193 through circuit breaker 1A14CB1. When the ON/VOLUME control on Receiver-
Transmitter RT-1209/URC is turned ON, power is applied to all circuits in system.
2-20. In the power amplifier, the +26.5 Vdc is applied directly to RF Driver 1Al 1, ALC Module 1A7,
Filament Regulators 1A14A6Q4 and Q5, Meter Board Al1, DC Control PWB 1A2, and System Control
Board 1A3. The +26.5 Vdc is also used to develop +1600 volts in Dc-to-Dc Converter 1Al4A3 that is
controlled by High Voltage Module 1A13. The +1600 volts is applied to the plates of RF Amplifier tubes
lAl4V1 and V2, while an Ip SENSE signal is applied to ALC Detector 1A7A2, DC Control PWB 1A2, and
Meter Board 1A1. The +26.5 Vdc is applied to Voltage Regulator 1A14A6Q3 to develop the +19 Vdc
which is used to derive the -14 Vdc in Meter PCB 1Al.
2-22. The +26.5 Vdc is applied through a normally open 55C thermostat (lA14A3S1) to the input of
Static Power Inverter 1A12. When the power amplifier temperature reaches 55C, the +26.5 Vdc is
turned ON, thus supplying a 400 Hz, 20 volt drive to axial-flow Fan 1A14B1. The power amplifier is
forced-air cooled by the fan which is external to the sealed case-cover assembly. When the system is
operated intermittently in the Tx mode, the blower never starts. However, under continuous Tx mode
operating conditions and high ambient temperatures, the blower runs continuously. When the heat-sink
temperature has cooled to about 54C, the fan is turned OFF.
2-23, The power amplifier is also protected from overtemperature conditions by Overtemperature
Thermostat 1Al4A3S2 (normally open), which applies a GROUND to System Control Board 1A3, when
the sink temperature reaches 96C, thereby shutting down the entire power amplifier.
2-25. In the AN/MRC-l 38 vehicular configuration, external meter 1Al4M1 and the six front panel
indicators are the only monitoring devices available on the power amplifier without opening the case-
cover assembly. The meter (1A14M1) normally shows the forward power output in the transmit (Tx)
mode, The RDY indicator lights GREEN one minute after power-up if no faults are present. The XMT
indicator lights GREEN in transmit (Tx) mode when the PTT (press-to-talk) or CW switch signal is keyed.
The TUN indicator lights AMBER during the sixty second warmup period and whenever the power am-
plifier is in Tune Mode. The FIL FAULT indicator lights AMBER when a tube filament has failed. The
PA FAULT indicator lights RED when there is a fault relating to the power amplifier, The CPLR FAULT
indicator lights RED when there is a CPLR fault.
2-27. For test and troubleshooting the power amplifier, the same meter (1A14M1) is used in conjunc-
tion with TEST SWITCH 1A1S1 on Meter Board Assembly 1A1. This allows the operator to select and
measure the following voltage and power levels in the power amplifier:
a.
+26.5 Vdc
CATHODE LEVEL
g.
b.
V1 FILAMENT
h.
Ip SENSE
c.
V2 FILAMENT
i.
ALC
FWD RF PWR
d.
+19 Vdc
j.
k.
RFLTD RF PWR
e.
-14 Vdc
f.
+1600 Vdc
