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Post subject: 1965 Twin Reverb (not reissue) Loud Building HUM problem
Posted: Sat Jul 31, 2010 12:36 pm
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So my '65 Pre-CBS twin had just been serviced a few months back. It has all new tubes and was checked out by a very credible guy here in Portland who has now moved to LA.
It was working just great until i switched it on one day and it started to hum and it gets louder and LOUDER like it going to explode. When i switch it back to standby it POPS super loud. Now it just sits in the corner, a damn shame.
I know nothing of repair or anything technical which is why i brought it in, in the first place. I don't want to spend another $300+ if i don't have to. But I also want to have that beautiful sound back.

Any suggestions? keep in mind i am technically ignorant.
Any educated opinions would be greatly appreciated.
I can provide pics for diagnostic purposes.


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Post subject:
Posted: Sat Jul 31, 2010 3:00 pm
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Joined: Wed Mar 31, 2010 12:48 am
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Location: Tombstone Territory
I'd look to the bias and/or filter caps first.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Sat Jul 31, 2010 5:55 pm
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I'd agree, it maybe a main filter cap(s) have gone bad. Try this one trick first, though. Pull all the power tubes and use a little contact cleaner on the sockets and pins. I use CAIG D5 Deoxit. Dry off any excess cleaner & reseat the power tubes. Sometimes, these older amps contacts become bad and you lose bias or some grid contact and the power tube(s) starts to runaway. Try re-seating them a couple of times. Then, turn on amp and see if you have the same problem.

If the tube's fit seems sloppy, the sockets may need to be tensioned. I usually do this with the amp out of the cab and the filter caps drained. Whether you need to tension the sockets or redo the filter caps, prolly best to hunt down another amp tech in your area.

HTH & good luck!


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