My 'Dyne, she be dying

[Talus]

So I turn my amp on, leave it in standby for 30sec to a minute.

Start playing. Volume drops, comes back, rapid pops. Treble drops, treble comes back, nothing but treble. High pitched squeal, static and so forth. It basically goes completely nuts for 15-20 seconds then resumes normal operation. Played for 15 minutes with no problems.

Turn it on again today, same deal.

I would expect this to have something to do with the tubes, but I've never ever had an amp go completely haywire before, and I'm not really sure how to be diagnose the problem beyond spending a large amount of cash to replace who knows how many tubes and the amp is only 8 months old if that.

Thoughts/suggestions on what it could be and what to do about it?

 

[screamingdaisy]

Sometimes a tube will fail mechanically, then when it heats up and the internals expand it somehow manages to function normally for awhile.

Tap the power tubes while the amp is on. If it induces the same noise and/or redplates then the tube has had a mechanical failure. If nothing, do the same with the preamp tubes... although I'd suspect the power tubes first.

 

[elvis]

+1

I have had TERRIBLE reliability problems with tubes lately. And the only active circuitry in a tube amp is the tubes. So I would bet on that. Try running in 45W mode and see if it still happens. Then swap the middle power tubes with the outer tubes and try again to see if you can isolate the tubes.

 

[J.J]

I would expect this to have something to do with the tubes, but I've never ever had an amp go completely haywire before, and I'm not really sure how to be diagnose the problem beyond spending a large amount of cash to replace who knows how many tubes and the amp is only 8 months old if that.

Time is almost irrelevant with tubes. They can go at any time, even within minutes. A spare set of tubes is well worth having in waiting for when you need them.

My amp is "only" 10 months old and is showing signs of the original power tubes being on their way out.

 

[tubby_cosmos]

I'd second the tubes diagnosis. They just go when they feel like it, unfortunately. Those symptoms sound an awful lot like what happened to my amp when the tubes died, and although I wasn't able to identify a microphonic tube at the time, everything got better when I swapped out the tubes. I've found I've needed to change my tubes almost annually when running the amp on the 45W mode primarily and probably a few hours a day 3-4 days a week.