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And with those sockets removed, and the am powered up, do the conditions still exist?
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Education is what you're left with after you have forgotten what you have learned. -
Yes... the conditions still exist. On the left pair, when I turn the high voltage on, it is present on both pins 4 and 5...Comment
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Here's your problem. You need to find out where high plate or screen voltage leaks into the grid circuit.Originally posted by Danglin' Fury View Post
Start with checking the X18/X15 connectors.
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Already did. I removed them, cleaned the boards thoroughly and then reslodered them... I've been soldering through how and SMT for 14 years now. I used plenty of water soluble flux and made sure there were no solder bridges. Still there. What about the choke? Could it be a turd? Would that manifest this issue? I cant see how but I'm just spitballing here. I don't see how 1 side can be ducky and the other side be all screwed up and it NOT be on the power tube board somewhere...Comment
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EUREKA!!!! I found it! X22, where the choke plugs in to the main board. I couldn't see the burn because of the connector plus the board itself is black. But there is a carbon "trace" from one leg of the choke to pin number 5 of X18. Boom. I'm gonna clean that up and then report back.Comment
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SUCCESS!!!!! Well, mostly. I can turn it on fully and it passes a signal and it gets loud with no fuse poppage BUT! Now there is a pretty loud hum emanating from the amp, like an instrument cable plugged into an amp and when you touch the tip. It is unaffected by the volume, i.e. it is the same loudness all through the volume sweep, however... When I turn Volume 1 to 1:00 and past that, it makes a farting sound... Very motorboat-ish. Any ideas? Power supply maybe? I rolled all the preamp tubes and that was definitely NOT the problem. And THANK YOU to everybody throwing me ideas. This truly is one of the best forums on the net. Period.Comment
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So the parasitic oscillation was a bad preamp tube. It cracked all the way around. Lol! I noticed it was white yesterday when I was about to do some measurements and I went to pull the 12ax7 out and only the glass envelope came off... lol! I finally got it out with some pliers and put a different one in its place. The oscillation is gone when I turn the Volume 1 knob past 1:00 now but i still have a nasty loud hum that REEEEEAAALLLY sounds like a bad filter or coupling cap.Comment
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