An rf voltage sample

TM 11-5820-509-35

power mode , the amplifier plate voltage is limited to

excessive distortion in the transmitted signal. This

+650 volts dc (derived from the normal screen voltage

automatic level control (alc) is accomplished by

power supply) and the screen voltage is correspondingly

reducing the gain of the transmit if. input signal

reduced to limit the screen-grid dissipation to reasonable

whenever excessive drive is detected at the power

values during periods of off-resonance operation. The rf

amplifier grid circuit. The (alc) voltage is developed

current flowing in the output circuit of the power

across grid resistor R104 whenever the power amplifier

amplifier stage is monitored by XMTR OUTPUT meter

draws grid current (class A B2 operation), and this

M101 to determine when proper resonance conditions

negative bias is added to the -110 volts dc used as a

exist in the output coupling network. Current bans

reference and the combined total (alc) sample controls

former T101 samples the output rf and develops a

the gain of (alc) amplifier Q1 in amplifier-modulator A2.

voltage across resistor R129 that is proportional to this

c. An rf voltage sample is taken from the plate

current. Diode CR102 rectifies this rf voltage and

circuit of the power amplifier across the voltage divider

applies it to meter sensitively adjustment (M ADT)

consisting of capacitors C105 and C144. This sample is

R117. Diode CR103 protects the meter from voltage

routed to the filament centertap of driver V3 in signal

overloads, and capacitor C106 bypasses rf currents

data translator A3 as a negative feedback that improves

around the meter movement. When the BATTERY

the linearity of the rf output signal. Another voltage

TEST switch on the front panel of the receiver-

sample is taken from the power amplifier plate circuit

transmitter is pressed, XMTR OUTPUT meter M101

across capacitor voltage divider C124-C140.

This

measures the terminal voltage of the connected

sample is rectified by sidetone rectifier CR101, filtered

batteries. Closure of this switch also overrides thermal

by capacitors C125, C126, and resistor R108, and

cutout K103 for emergency operation of the receiver-

applied as an enabling bias to sidetone gate CR10 in

transmitter during overtemperature conditions in the

audio frequency amplifier A1. XMTR PWR switch S103

power amplifier compartment.

The POWER

on the front panel of the receiver-transmitter selects the

AMPLIFIER LOAD and POWER AMPLIFIER TUNE

appropriate XMTR OUTPUT meter range, power

controls operate inductors L109 through L112 and the

amplifier control grid bias, and power amplifier plate and

whole megahertz control selects an appropriate shunt

screen voltages to assure linear operation of this circuit

capacitor from the group C108 through C121 to

at reduced power levels during tune-up and preliminary

terminate the power amplifier plate circuit impedance.

loading adjustments. In the LOW

2-32