Power tubes not glowing.. no sound.. wtf

[ChmpgnSupernover]

So I was gonna have the house all to myself for the next week and what do you know my only amp blows!

First off, this is a Peavey Classic 20 tube amp and its the only amp I have at the moment.
I was playing through it a few days ago and the volume gradually cut out over the period of about 10 seconds to the point where the amp was completly mute. I looked in the back of the amp and the two EL84s were not lit. I switched all the tubes out with some replacements I had sitting around (although its possible some of them are old) but yet I am getting no sound from my amp and the power tubes are not lit while the pre-amps are.

What happened?

[WaltC]

It's very common for the classic 20's and classic 30's to have problems with the tube heater solder joints on the pc-board. The tubes are daisy chained and if one solder joint breaks down then all the tubes down stream from that solder joint go dark.

Not particularly easy to work on. The pc-boards (there are three) are ribbon-connected in a small "U" shape and the heater joints are on the inside of the "U". All the tube sockets are board mounted.

FWIW

[ChmpgnSupernover]

Thanks! I've had the boards out before and yea, its quite cramped in there! Although I've never worked inside an amp I do know how to weld and I've built a dozen or so computers so I know my way around electronics (and to keep my hands away from the capacitors), so I'm gonna give it a look tomorrow and see what I think I can do.

Are there any resources that will help me learn the precautions to take when working inside a tube amp?

[skipm45]

Look under "tech info / safety precautions"

http://www.aikenamps.com/

Aiken has lots of other technical articles to enhance your understanding of tube amps.

Skip
www.skipzcircuits.com (http://www.skipzcircuits.com)

[rockon1]

Heres a good link. Enzo is pretty knowlegdable with peavey stuff. Check out his post 4th down. Turned out to be a brokn jumper wire. Bob

http://music-electronics-forum.com/showthread.php?t=11162


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[triodeamps]

Remove the board from the chassis and repalce the EL84 tube socket with ceramic ones. EL84 tube get so hot that i have seen the pins of the socket burn and not conduct voltage between the PC board and the socket itself. That will cure your problem. Though you may have a bad bias resistor and cap. In any case change the EL84 sockets. It's not all that bad to do. Just have to have done it enough times so it is easy after a while....

[ChmpgnSupernover]

I did it! Whew. There are these little jumpers that connect the circuit boards to each other and one of them broke. I just put a gob of solder on there and it worked. The one that was broken was right under the V4 socket.

[rockon1]

Heres a good link. Turned out to be a brokn jumper wire. Bob

http://music-electronics-forum.com/showthread.php?t=11162


........

I did it! Whew. There are these little jumpers that connect the circuit boards to each other and one of them broke. I just put a gob of solder on there and it worked. The one that was broken was right under the V4 socket.

Did I win? :banana

[ChmpgnSupernover]

Did I win? :banana
Yes thank you very much for your help! I didn't actually know what I was looking for when I went in there but the link gave me an idea where to look. Why would something like that break?

[rockon1]

Yes thank you very much for your help! I didn't actually know what I was looking for when I went in there but the link gave me an idea where to look. Why would something like that break?

Enzo knows Peaveys.;) Also a lot of good tech info over there.At any rate I can only imagine vibration stresses the wire over time. Bob

[rockon1]

More specifically-

Quote: Enzo-
" it is from vibration. The boards vibrate around in there from the speaker being nearby. The wires can break.

This same exact board layout would not be breaking jumpers if it were just a head. (No speaker.)"