Squeal in 6L6 - Is it close to death?

S. F. Sorrow

Member
Messages
8,790
Lately if I'm playing loudly one power tube has a quiet squeal to it - kinda sounds like someone stretching a balloon. If I stop playing it goes away several seconds later.
The tubes I know are wearing out but it ready to blow?
Even when new, the tube seemed to have a 'penny in a bottle' rattle to it when the cab would thump.
The tube is a JJ 6L6 over two years old in a Frenzel 50w head w/4x12.
Thanks!
 

S. F. Sorrow

Member
Messages
8,790
You mean a squeal as in you hearing it in the speakers or you as in hearing it acoustically?

The speaker. I think it may be acoustical too. It's kinda quiet. I'll have to remove the cage tomorrow to listen closer.
When I play loud it seems like the tube keeps ringing or oscillating for a few seconds after I stop.
Almost like a metallic glassy squeal.
 

swiveltung

Member
Messages
14,483
I doubt it has anything to do with failing. Some brand new tubes squeal. Although not a lot of them.
 

Tone Meister

Member
Messages
3,266
Yeah, a squealing or microphonic power tube is pretty rare, but it does happen.

Try this with the tubes warmed up: with a gloved finger or maybe a pencil eraser, put moderate pressure on the glass and see if that will quieten it. If so, you may be able to get a dampener similar to those ubber rings for preamp tubes and squeeze some more life from it. With a power tube, it's not like you can hide it in the phase inverter or tremolo circuit like you can in a Fender amp
 

modernp

Senior Member
Messages
3,550
Why risk it. If a power tube fails it can take out other components such as screen resistors.
 
Messages
7,833
The speaker. I think it may be acoustical too. It's kinda quiet. I'll have to remove the cage tomorrow to listen closer.
When I play loud it seems like the tube keeps ringing or oscillating for a few seconds after I stop.
Almost like a metallic glassy squeal.
Yeah, then it's probably rattle induced microphony and you better replace that pair of valves. I agree w. others that it could take other components with it in the fall, so not worth risking your amp for.
 

Laurence

Gold Supporting Member
Messages
10,413
Have you completed the chopstick/pencil test? It could be that tube, or another or something on the board, or....

I've experienced this type of issue, and sometimes its a power tube, sometimes a preanp tube, sometimes a flexing/damp phenolic board, sometimes a faulty reverb tank...
 

S. F. Sorrow

Member
Messages
8,790
Have you completed the chopstick/pencil test? It could be that tube, or another or something on the board, or....

I've experienced this type of issue, and sometimes its a power tube, sometimes a preanp tube, sometimes a flexing/damp phenolic board, sometimes a faulty reverb tank...

Yeah, I've done the pencil test and it rings like hell. But it ringed even when it was new. I assumed it was a bad spacer that wasn't tight against the glass and was rattling. It's the squealing I find troubling. Never heard anything like that before from a power tube.
Guess I'll put some KT-66 to warm the house until the new tubes arrive.
 

Laurence

Gold Supporting Member
Messages
10,413
Yeah, I've done the pencil test and it rings like hell. But it ringed even when it was new. I assumed it was a bad spacer that wasn't tight against the glass and was rattling. It's the squealing I find troubling. Never heard anything like that before from a power tube.
Guess I'll put some KT-66 to warm the house until the new tubes arrive.

I think i've previously stated I like your handle, but if I haven't, I really like your handle! What a great album...

I've had power tubes go microphonic in this manner, although it it's pretty rare. Usually it's just a slight bit of mechanical noise, especially in a hign gain combo, but they can squeal like a preamp tube under the right conditions. Just make sure the sockets are tight and snug (on the chassis and the pins themselves) when you replace the tubes.
 




Trending Topics

Top Bottom