microphonic chassis problem

[ampcabinets]

If you want as little hum as possible, you want DC heaters.
You want to use silver mica caps, especially on the volume control bypass, or bright switch.
BUT get your power receptacle grounded properly FIRST.
USE the receptacle tester, to confirm there IS a proper ground FIRST.

ground was never a problem.
I have several testers, including several digital meters and my house is wired properly, and always has been.
Thanks for the suggestion, tho'

I always use the best caps I can get, period. Thanks for your input, tho'

I have been through the tubes and back again, found 1 loose ground (loose, not disconnected).
I replaced the caps (microphonic) in question with no diference. In fact I replaced several, back down the preamp chain, just to be sure.
I even ran some shielded wire on some conenction and that didn't change things either.
The noise gets louder the closer to bias I am. It is biased at 42 ma at 400 v., which is just a bit cold. Raising it to 45 or so will just make it louder, not go away.
The buzz is pretty loud.

The showman, I'm working on, doesn't have a cap cover and I suspect that is part of the buzz (not hum)...there is no hum at this point.
I am working on a cap cover for it and should have it finished soon. I'll post back.....
The amp is loud and clean, and bright, beyond that.

still working on it.

[Alex R]

just a thought - does the hum go away if you simply touch the chassis, anywhere?

[soundguruman]

ground was never a problem.
I have several testers, including several digital meters and my house is wired properly, and always has been.
Thanks for the suggestion, tho'

I always use the best caps I can get, period. Thanks for your input, tho'

I have been through the tubes and back again, found 1 loose ground (loose, not disconnected).
I replaced the caps (microphonic) in question with no diference. In fact I replaced several, back down the preamp chain, just to be sure.
I even ran some shielded wire on some conenction and that didn't change things either.
The noise gets louder the closer to bias I am. It is biased at 42 ma at 400 v., which is just a bit cold. Raising it to 45 or so will just make it louder, not go away.
The buzz is pretty loud.

The showman, I'm working on, doesn't have a cap cover and I suspect that is part of the buzz (not hum)...there is no hum at this point.
I am working on a cap cover for it and should have it finished soon. I'll post back.....
The amp is loud and clean, and bright, beyond that.

still working on it.

What you are describing is a bad supply ground.
None of those meters tell you what the $7 tester tells you.
If you had a good supply ground on the chassis, half these problems would not be there.
There is no need to troubleshoot and tear the thing apart to compensate for a ground that is missing.

[ampcabinets]

What you are describing is a bad supply ground.
None of those meters tell you what the $7 tester tells you.
If you had a good supply ground on the chassis, half these problems would not be there.
There is no need to troubleshoot and tear the thing apart to compensate for a ground that is missing.

please see pictures and point out where my supply is wrong.

It has been good for the last 30+ years, why would it change now?
Please refrain from telling me this is bad, again, and or saying things meant to belittle others.
I told you all I checked everything before.
If you don't want to believe me, then, by all means, stop trying.

It is good at the wall, or it wouldn't be good at the bench.
It is good in the amp, or it wouldn't power up and measure correct voltages on the amp., at the incoming supply, etc.
The ONLY thing I haven't done that I have done in the past 200 or so builds, is to run a ground buss down the back of the pots.
I may try that in the future, but I don't see how that would make that much of a difference, but I have seen it make "A" difference.
AND if the ground was missing from the amp, I would HAVE to tear it down to get at it. As it is, it is already on the bench, and open, so "TEARING IT APART TO COMPENSATE FOR """ANYTHING"""" wouldn't be a problem.
You may call yourself a guru, but I think you are just another person who may or may not know something about electronics. Probably more than me, but not by much.
There is ALWAYS someone better.

Please calm yourself down. It isn't THAT big of a problem, or THAT big of a deal.
MY 30lb sledge hammer can fix almost anything, including a 1963 showman, to which I am NOT attached.

I have tried to be very civil, but I can change that if you wish..