Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mamps on July 06, 2010, 12:12:34 am
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Hello there,
I have a jcm800 clone that is making a terrible high pitched squeal when the master volume and gain both reach about 7. When i turn the master down, and crank the gain to 10 it sounds clean (no squeal). It is only when the master volume gets high.
I would take the scope to it but i am out of town right now and thought i would try to get an idea of what the problem was prior to getting home.
Any input would be much appreciated!
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Reversed plate leads on the OT,lead dress,wrong negative feedback loop resistors.There are other things that may be the culprit but those are the most likely.
If it was wired right,it would be working.The lead dress is not that critical in a JCM800,but the plate leads could easily be reversed.
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New build? Or did a older build just start doing it? Chop sticks can be your friend on a high gain amp... Move a few wires, sometimes just the placement is enough to get the squeel going...
D.
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Are you using any shielded wire? How about that "cheater" snub cap on V1a? I'm betting you have the brite cap installed....
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Yeah its an older build that I bought off a guy in town. I built a new cab for it and since moving the chassis over and getting it fitted properly the noise has come up. Im out of town and havent been able to take a closer look, but i have a feeling that some chopsticks may do the trick.
And no shielded wire in this one. I will update when I get a chance to move some leads around!
thnx fellas