5018 POWER AMPLIFIER

TM 11-5820-918-13

4-39. 5018 POWER AMPLIFIER - UNIT 2

4-40. The power amplifier unit (figures FO-21 and FO-22) consists of the 100-watt

amplifier assembly (2A1), the power supply assembly (2A2), and the enclosure assem-

bly (2A3). The 100- watt amplifier assembly contains the 32 MHz low pass filter

(2A1A1) and power amplifier subassemblies (2A1A2). The power supply assembly

provides all the regulated DC power for the 100-watt amplifier assembly. The en-

closure assembly (figure FO-22 ) contains the chassis and the rear panel subassembly

(2A3A1).

4-41. 32 MHz LOW PASS FILTER (figure FO-21/1). Assembly 2A1A 1 is an LC low

pass filter to attenuate frequencies above 32 MHz. This assembly receives the RF

signal (2- 30 MHz) from the synthesizer and provides an output to the power amplifier.

4-42. POWER AMPLIFIER (figure FO-21). The power amplifier consists of a driver

circuit (2A1A2A2), a four-way power splitter/combiner circuit (2A1A2A3) and four

identical 30W power amplifier circuits (2A1A2A4-A7). The driver circuit consists of

a class A linear preamplifier followed by two parallel class A push-pull driver ampli-

fiers. The RF gain from the preamplifier input to each driver amplifier output is ap-

proximately +38 dB. The nominal full power input to the driver preamplifier from the

1024 is approximately 0 dBm. This yields an output power level for each driver of

5 to 10 watts (typically 7) when the TCS-4B output is 100 watts. Of the two 10-watt

driver outputs, one is used as the input to the power splitter/combiner (figure FO-

21/3), and the other is used to drive the filter decode module in the 4011 unit.

4-43. The 10-watt signal from the driver circuit is impedance-transformed and split

by the power splitter to form four identical signals which feed the four 30-watt power

amplifiers. Each 30- watt power amplifier (figure FO-21/4) consists of a two transistor

class A push-pull, transformer coupled, broadband linear amplifier. Each output

transistor (Q1 and Q2) is biased to 2.75 amps collector current (5.5 amps total) by

integrated circuit bias regulator U1. Each of the four amplifiers has a gain of 14 dB

and produces up to 30 watts at each of their respective outputs. The power combiner

adds the four 30-watt signals to produce the final output of approximately 100 watts.

The RF power is impedance transformed to 50 ohms and presented to the output con-

nector J3.

CAUTION

The amplifiers, splitters, combiners, and RF cables are carefully phase-

matched to ensure proper division of RF power throughout the amplifier.

Any change of coax cables connecting the power splitter/combiner could

seriously degrade the amplifier performance.

4-44. 5018 POWER SUPPLY (figures FO-23 and FO-24) (S/N 400101 and on). This

circuit accepts 115 or 230 VAC at 47-440 Hz and produces the following outputs:

a. 115 VAC, 60 Hz - three independent supplies for the rear panel-mounted cooling

fans.

b. +27 VDC - five independent supplies for power amplifier circuits.

c. +5 VDC - one supply for the front panel power indicator lamp.