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This amp had a bias drift issue, I have repaired it and all is well on that end. It does however had a hum that sounds 60 cycle almost on channel 1. I have cleaned the EFX loop already but it appears to help a lot if I jump the loop over(I can use fx knob to control channel volume). The low button or the presence also does not work unless the efx if jumped over. I’m not sure if I’m tracing a channel 1 issue or loop issue. The other 2 channels are seemingly quite Also. With a scope I am seeing a lot of noise around FET1 and opto 1&2 which is early in the channel 1 chain. Any ideas where to go?
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Trying to add the schematic -
The address is incomplete.Originally posted by pnut5150 View Post
https://www.google.com/search?q=http%3A%2F%2Ftubes
Maybe ?
http://www.tubes.rs/
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With the rear vent panel removed, so you have access to the bias test points and both bias trim pots, are you finding them drift on both upper/lower halves, or just one half? I've had to extract that bias PCB assy when this occurs, which of course is a PITA, then often find one or more of the connections to/from the bias board with solder joint issues, plus seeping in a touch of DeOxit into the pots and exercising them. Then, of course, you have to reset/bias up the amp again to watch the results. I thought I had some photos of that operation & PCB, but didn't find them.Originally posted by pnut5150 View PostLogic is an organized way of going wrong with confidenceComment
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