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Hi, I have a pair of the AP-55 mono amps that I have been restoring, and while I have gotten them to work well, I have a bit of a buzz (120 hz) in the output. The scope shows 25v p-p as a sawtooth. These have new PS caps in them at the same value (30 ufd) that comes from a pair of 5Y3 rects. I would have assumed that these amps would not have had this buzz in them from the factory, but, other than the output tranny hookup, I am a bit flummoxed on this particular problem, any suggestions? I note the output tranny connection has me scratching my head, it has three windings, one for the output tubes (primary) and 2 for the secondary, one winding side going to the neg feedback loop with the other end shown as ground, and the other winding going from 0V to 4, 8, 16 ohm up to 70 V. I assume that I would connect from ) to 16 ohms, correct, not from the ground to 16 ohms, is that correct? Also, should the ground connection be connected to the chassis ground or? thanks!
Follow Ups:
I restored a pair of Stromberg Carlson APH-50's with completely new PSU caps, signal caps, a few old resistors and new tubes.... the same 120 Hz hum is present.
The only way I was able to reduce the hum was ny using Vintage 5U4G rectifiers vs. the Sovtek's. But the hum is still audible from 2 feet away. As long as the music is loud it doesn't affect me, it's between songs that the 120Hz bothers. I guess I have learned to live with the imperfections and listen through them.
As far as the speaker connections are concerned, I jumpered the relay connector board direct to the 8 Ohm and Ground connection on the Octal Output Socket.
I would assume that the safet place for the ground is the DC Ground and not the Chassis ground, but you can experiment with both and see which works best.
Often with equipment of this vintage, the Chassis and DC ground are the same.
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