Valva amp threw a wobby last night...any thoughts please?

[Nick]

Yep, I can't make out from the picture just what its doing, but it may be part of the driver stage. Doesn't look that badly overheated, but would be nice to know just where it goes.

[gazjam]

Big thanks to Ali for taking the time to look at my amp.
Great that the voltages check out, good piece of mind.

Ali suggested some internal upgrades for me, caps, stepped pot etc, so will need to take those circuit boards off to do the work.
Will post better photo's of that browned out resistor and where it goes.
Thanks guys.

Only question is what might have happened?
Amp sounds and measures fine...hopefully sweep this one under the carpet.
Got some new KT88's on the way just in case, Svetlana Winged C's, so should be good.

[gazjam]

Anyone have any info on the big blue caps in the photo?
Looked at everything else for upgrading but don't know if these are any good or not.

Couldn't twist them round to get manufacturer info or anything off them either.


thanks.

[Paul Barker]

Only question is what might have happened?
Amp sounds and measures fine...hopefully sweep this one under the carpet.
Got some new KT88's on the way just in case, Svetlana Winged C's, so should be good.

I am not familiar with KT88 amps but if the components test OK it may be a valve problem.

[Mike H]

I've just had a thought (dangerous in itself .....)

You turned it off then on again rapidly. (Well actually the conditioner, but the amp was on meanwhile, so same difference.)

Amp uses fixed bias.

You turn it off, cathodes are still hot.

Turn it on again quickly before cathodes go cold, the KT88's start up again, but now with zero grid bias.

Result: glowing red anodes.