TM 11-5820-921-40-1
to 60 ampere capacity (i.e., 45 amperes for the power amplifier plus the drain of the antenna coupler, the
receiver-transmitter, and any auxiliary equipment). The +26. 5 Vdc is applied directly to Receiver-
Transmitter RT-1209/URC through connector 1A14J 2, pin L, and Amplifier-Converter AM-6879/GRC-l 93,
and to Antenna Coupler CU-2064/GRC-l 93 through ANT CPLR circuit breaker 1A14CB 1 and connector
1A14J1, pin M. Dc power is applied to the system only after the receiver-transmitter ON/MAX VOLUME
control is switched to the ON position, which sends ground signals (PA ON/OFF and ANT CPLR ON/OFF)
to the power amplifier via the amplifier-converter. The PA ON/OFF signal ground is applied to System
Control PWB Assembly 1A3 to enable the DC RELAY (ground) signal which energizes POWER ON relay
1A14K1. The +26.5 VDC DIRECT power is applied through the POWER ON relay as the +26.5 VDC
SWITCHED power (see figure 2-5 and 3-78) for distribution within the power amplifier.
2-129. +26.5 VDC SWITCHED POWER (See figures 2-5 and 3-78)
2-130. The +26.5 VDC SWITCHED power is routed to Antenna Coupler CU-2064/GRC-l 93 thru con-
nector 1A14J1, pin L. The +26.5 VDC SWITCHED power is applied to Junction Block PWB Assembly
1A14A5-E3 where it is distributed to RF Driver Module Assembly 1A11 through 1A14A5-E7, to ALC
Module Assembly 1A7 through 1A14A5-E6, to the V1 Filament Regulator 1A14Q4-C, the V2 Filament
Regulator 1A14Q5-C, and the +19V Regulator 1A14Q3-C through 1A14A5-E2, to Interconnection PCB
Assembly 1A14A1 through 1A14A5-E5, to FAN/LAMP test switch 1A14S l-C-l through 1A14A5-E4,
and to the 550 NORMALLY OPEN THERMOSTAT switch 1A14A3-S 1-1 and the High Voltage Module
Assembly 1A13 through 1A14A5-E1. The +26.5 Vdc is also applied across inductor 1A14L1 to the
center tap (pin 2) of step-up transformer 1A14T 1. The primary winding of 1A14T 1 is connected to
transistor 1A14A3Q1-C (from 1A14T 1-3) and to transistor 1A14A3Q2-C (from lA14T1-1) in the Dc-to-
Dc Converter Module. The secondary winding of 1A14T 1 is applied to High Voltage Module 1A13
through connector 1A14J13-H (from 1A14T1-5) and 1A14J13-J (from 1A14T1-4).
2-131. +19 VDC SERIES REGULATOR (See figures 2-9,3-66, and 3-78)
2-132. The +19 Vdc voltage regulator consists of series pass transistor 1A14Q3, driver 1A2Q4, sensing
amplifier 1A2Q5, and voltage reference zener diodes 1A2VR2 and 1A2VR3. The base voltage of sensing
amplifier 1A2Q5 is held constant by zener diode 1A2VR2 (at +10V). Output voltage variations are sensed
across emitter resistor 1A2R18 through zener diode 1A2VR3 (- 10V drop). When the output voltage
increases due to input voltage or load change, conduction through driver 1A2Q4 and series pass transistor
1A14Q3 decreases, reducing the voltage at the emitter of 1Al4Q3. If the output voltage decreases, the
circuit acts just the opposite, with increased conduction through 1A2Q4 and 1A14Q3, increasing the
emitter voltage of 1A14Q3. Therefore, the output voltage is maintained constant.
2-133. If there is a short circuit on the +19 Vdc line, the base and emitter voltages of sensing amplifier
1A2Q5 simultaneously go to zero, cutting OFF both 1A2Q4 and 1A14Q3. Resistor 1A2R 6 bypasses
the 1Al4Q3 transistor in order to restart the regulator circuit after the short circuit condition disappears
or has been corrected. Without resistor 1A2R16, all of the transistors would be cut off and could not
restart because there would be no bias voltage present. With resistor 1A2R16 in the circuit, transistor
1A2Q5 is biased through resistor 1A2R17 to start to conduct as soon as the regulator output is no longer
shorted (normal load). The value of 1A2R16 is large enough so as not to affect the normal operation of
the regulator circuit. Capacitor 1A2C3 is used to filter the regulator output. Regulation is maintained
within about 0.2 Vdc of the nominal 19.5 Vdc output with the actual absolute voltage value depending
on the tolerances of the zener diodes. There is no voltage adjustment provision because the abosolute
output voltage is not critical.
2-135. The -14 Vdc switching supply consist of square wave generator 1A1U 1 (approximately 20 kHz),
voltage amplifier 1A1Q1, and current amplifiers 1A1Q2 and 1A1Q3, coupling capacitor 1A1C4, rectifiers
1A1CR2 and CR3, and filter capacitor 1A1C5. The -14 Vdc output is not critical; therefore, it is not
regulated.
