Atlas 210x, Installation, Operation And Maintenance Manual

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4-14. PC-500D/520A Pre-Amplifier, Driver, Power Amplifier, SWR Protect
The R.F. output from PC-200C is coupled through the Transmitter Input Tuning circuit (PC-900) to the input
connection on PC-520A. From the input connection, the signal is coupled through C504 to the base of the Pre-
Amplifier Q501, where it is amplified and coupled through C501 to the base of Q502 for further amplification.
From Q502, the signal is coupled through the Toriod interstage transformer T501 to the base of the Driver Q503
on PC-500D. The output of the Driver is coupled through the Ferrite Core Driver Transformer T502 to the base
inputs of Q504 and Q505, which are the Power Amplifiers. The outputs to the Power Amplifiers are coupled
through the Ferrite Core Output Transformer T503 to the output connection on PC-500D. From this connection,
the output signal passes through relay RL1, through the Low Pass Filters PC-100/1020 to the 50 ohm antenna
connector.
Q506 is a bias regulator for the output stage. Trim pot R515 is used to adjust resting current collector to
approximately 1/2 amp. Diodes D501 and 502 regulate the bias circuit, and are thermally connected to the heat
sink in order to sense temperature increase. Thus, bias voltage automatically increases with temperature,
preventing thermal runaway of the output transistors.
Reflected voltage which is generated by a mismatch in the antenna system is rectified by D1102 and D1103 on
PC-1100A in a doubler circuit, filtered, and then connected to Q507, the SWR protect circuit. There it is used to
reduce the gain of the first pre-amplifier, thus reducing drive to the power output amplifier. The trimpot R522 is
adjusted so that Standing Wave Ratios greater than 2 to 2.5 will drastically reduce R.F. drive.
PC-500D/520A CIRCUIT COMPONENTS
Pre-Amplifier, Driver, Power Amplifier, SWR Protect
C501,502,504,507,510,518, R503.514. ............... 470 10% 1/4 Watt
519,520,521. ....... .01 MF l00VDisc R504, 513. ............... 180 10% '/4Watt
C503.509................ 0.1 MF 50V Disc R505,506. ................ 47 10% % Watt
C505 ................. 37-250 pFTrimmer R507.508............... 1.5K 10% 1/4 Watt
0506,512,517.......... 0.1 MF100V Mylar R509 ................... 270 10% '/4 Watt
C508,516,522 ...... 15MF 100V Electrolytic R510 ................... 470 10% % Watt
C511.............. 2.2 MF 50V Electrolytic R512, 519 ................ 1.1 10% 1/4 Watt
C513.514 ........... 330pF5% Silver Mica R515 ..................... 1K Bias Adjust
C515........... .... 100 pF 5% Silver Mica T501 ......... Toroid
Interstage Transformer R516 ................... 560 10% % Watt R517 .................... 1010%
2 Watt
T502. ....... Ferrite Core Driver Transformer R518, 520 ................ 4.7 10% 1/4 Watt
T503 ....... Ferrite Core Output Transformer R521 ................... 220 10% '/4Watt
L501 ........................ 33uHRFC R522 ..................... 2.5K Trim Pot
L502 ....................... 1.4uHRFC R523.R524 ............... 1K 10% 1/4 Watt
L503 ....................... 0.6 uH RFC Q501 ................. MPS6514Pre-Amp
L504. ................ 3 Ferrite Beads, RFC Q502 .................. 2N3866 Amplifier
L505 .......... 1.5 uH RFC and Meter Shunt Q503.................. RCA 40582 Driver
L506 ................. 7.6 uH Toroid, RFC Q504.505 CTCCD2545 Power Amplifier
D501,502,503 ........ SI-05 Regulator Diode Q506 .............. 2N5490 Bias Regulator
R501 .................. 2.7K 10% '/4 Watt Q507 .......................... 2N3646
R502 .................... 10 10% 1/4 Watt