JCM Mini Clone Issues

imgumby001

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The OP never mentioned the dreaded squeal from having the primaries reversed but is there a chance that positive feedback is causing the tubes to redplate?
Ya, learned that one the hard way with my first real build, my 5f1. This little beast has never had that issue.
 

imgumby001

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Yeah, I was considering ultra-sonic oscillation as a possible cause. Not only reversed OT primaries, but also the lead dress. You can get away with way more when using PCB's, so maybe converting to hard-wired has caused problems. I was also curious about C23 (470pF) going to ground from the V4 grid stopper. Did they do that because of an oscillation problem even with a PCB?
My lead dress may not be the prettiest I’ve ever done, but I’m not having any noticeable hum or noise, and I can’t get anything to show up on the scope that looks like extra noise being picked up anywhere.
 

imgumby001

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So, just as an update to put this to bed for everyone, and much thanks to all who contributed. You guys have really, really helped me by doing some of my thinking for me!! I re-did my ground scheme. Moving the power, pre, and outputs all to separate grounds helped smooth everything out, a lot. R51 didn’t pass the poke test. It was only partially connected internally, so it was replaced. The 6l6’s that were in there got the trash can. After throwing in several different pairs I settled on some out of my silvertone 1484, some vintage sylvania’s that tested good, even if only at about 60%. Biased them all the way cold(approx 55% dissipation) and man, she actually sounds good. I’m not 100% that the circuit is operating at its optimum, but it’s NEVER sounded this good. Hooked her up to one of my 2x12’s with an ehx v30 clone and wgs g12c- put an overdrive out front(tc cinders) and a little delay/reverb(ghost drive) and I’ll be damned if she’s not a player. Maybe not 25w, but sounds as loud as my Panama fuego x, which I believe is rated as a fifteen watter. At the end of the day the thing works, does not redplate, had a decent lead channel and is useable. Once again thanks to you all, and hopefully one day I can give something back to this community that has helped me so very much!!!
 




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