This will light bright upon turn on and darken after caps charge. For the turn on test of the repaired amplifier use a LIGHT BULB (100w) in series.
All of the benches had a variac and wattmeter as part of the basic test equipment. Remember to verify any repair and always use an AC INPUT POWER WATTMETER. You need to run a Bode plot and verify the phase margin. Any one who uses the newer devices will have INSTANT FAILURES and SHORTED OUTPUTS unless you redesign the amplifier. Some of the common output devices today have Ft's to 10-15 MHz.
The Bandwidth of the Homotaxial devices were 600-800 KHz the Epitaxial-base are 2-4 MHz. New output devices may need some additional emitter resistance however the real problem will be stability as the outputs today have much greater Ft's. I do remember that both RCA and MOT changed the Mfg process in mid 70's and the parts were still "2N3055" however the stamped flange ID stamps were changed. (Thermal runaway after a short period of time,) If some one rewires and or changes the wire size as some repair tech have done, then FLAMES might be seen or the top copper trace on the pcb will open. The copper wiring of the modules along with the Vbe's of the RCA devices acted as the Emitter Resistors.
The newer parts will need additional compensation to have a stable amplifier. We did a 100% Vce and SOA test on each device. RCA made a change about 1976 to an EPI BASE type. It is a SELECTED RCA 2N3055 HOMETAXIAL type. Here is some interesting stuff from Duke regarding replacing old power transistors with new ones from Might take that cap, let me check this one,Īcoustic Forum-Duke Aguiar used to work at Acoustic in the early days and has a few post here>
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