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RE: Fisher Amplifier Voltages Questions

Posted by dls123 (D) on September 17, 2013 at 06:46:02

In Reply to: Fisher Amplifier Voltages Questions posted by Qman on September 16, 2013 at 18:02:04:

Hi
Possible the downstream cap(s) are bad, but also it appears there is a center tap on that winding(red/yellow). If the ground is bad then it will raise the resistance and therefore lower the output voltage. I have rebuilt more old Fisher gear than I can count and most had rivets for everything. Many rivets make poor chassis contact for the grounds after 50 years. If your meter doesn't go straight to zero and stay there for the resistance from that center tap ground to the chassis then knock out the rivet, put an internal tooth lock washer between the ground terminal and the chassis and put a good old screw in there to replace the rivet. Then measure resistance to ground. A good chance this will solve the problem. You should check all the ground points in the amp. Your hum will go down if you have any....

Rebuild the entire power supply if you haven't already and check the signal path caps, especially those .02 on the output tubes.
Good Luck!
Don

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