TM 11-5820-921-40-1
GENERAL INSTRUCTIONS
SECTION I
GENERAL DESCRIPTION AND SPECIFICATION DATA
INTRODUCTION
This manual provides intermediate maintenance instructions for Power Amplifier AM-6545/GRC- 193
hereinafter called the power amplifier), procured under Contract N00039-75-C-0022 (see figure 1-1). The
power amplifier is part of Radio Set AN/GRC-l93 and Radio Set AN/MRC-138. Its relationship to other
components in the radio set is shown in figures 1-2 and 1-3. Organizational maintenance instructions for
the power amplifier are provided in the system manual for the radio set, TM 11-5820-922-12.
FUNCTIONAL DESCRIPTION
14.
The purpose of the power amplifier is to amplify a selected HF (high frequency) input signal, in the
frequency range of 2.0000 to 29.9999 MHz. The input level to the amplifier from the receiver-transmitter
is from 50 to 100 milliwatts. The output level is 400 watts average or PEP (peak envelope power). The
power amplifier tunes automatically in response to bandswitching signals from the receiver-transmitter and
to its own internally generated fine tuning (servo) signals. The power amplifier distributes +26.5 Vdc
(nominal) primary power from the power source to the other radio set components, (the receiver-
transmitter and the antenna coupler). The 400 watt output is coupled from the power amplifier to the
antenna by the antenna coupler, which tunes automatically in response to bandswitching signals and RF
excitation from the receiver-transmitter. The unit amplifies a 100 milliwatt RF input from the receiver:
transmitter to 400 watts 1 dB average or PEP (peak envelope power) output power. Primary power at
26.5 Vdc (nominaI) is supplied to the amplifier from a vehicular battery-generator system, or from another
appropriate source, for distribution to the amplifier-converter, receiver-transmitter, and antenna coupler
units of the system.
The power amplifier consists basically of three major functional areas:
1-5.
RF amplifiers and PA control circuits
a.
Power and cooling circuits
b.
Monitoring and test circuits
c.
The RF amplifiers and PA control circuits include part of Meter Board PWB Assembly 1A1, RF
1-6.
Driver Module Assembly 1 Al 1, Tune Detector Module Assembly 1A10, Tube Socket Assembly 1A14A2,
Output Amplifiers 1A14V1 and 1Al4V2, Plate Assembly 1A9, Tank Circuit Module Assembly 1A8,
Harmonic Filter Assembly lA15, ALC Module Assembly 1A7, System Control PWB Assembly 1A3, Tune
Control PWB Assembly 1A4, Servo Amplifier PWB Assembly 1A5, and Band Control PWB Assembly 1A6.
The 100 milliwatt input from the receiver-transmitter is first amplified by a two-stage transistorized
wideband driver amplifier to an output level of about 15 watts. This output is used to drive the grounded-
grid power amplifier stage. The power amplifier consists of two parallel-connected type Y621B triode
vacuum tubes and a tunable
- network tank circuit that transforms the tube plate impedance from 1600
ohms to the 50-ohm output impedance. The 50-ohm output impedance matches the input impedances of
the antenna coupler and provides selectivity to suppress harmonic signals. Tank Circuit tuning is auto-
matic in less than five seconds, with the shunt elements selectable in eight bands by the motor operated
1A8A3B1 rotary switches 1A8S1-A through 1A8S1-C. The series coil is tuned to the proper inductance by
the servo loop and the drive motor.
