A power or volume drop on a Fender Supersonic

[MD57md]

I have a fender Super Sonic amp. It sounds great. but after about 3-4 hours of gig level playing the drive channel seems to loose about 25 -50% of its output.
If it was a tube would this occur sooner? It has happened about 4 times on a gig.
Looking for possibilities. transformer ? Tube?
I think it is possible that this is a needle in a hay stack. I don't know if a tech could duplicate the circumstances.
Any Thoughts or experience out there?
Thanks

[Jazz P Bass]

Fender SuperSonic

Yup.
A needle in a hay stack.
3 hours & then it starts to fail.
Is the Burn setting what you refer to as dirty?
Does it only fail on the dirty channel? If so that narrows it down considerably.
V1 & V3 are the burn channel. Try replacing them.
If it was on my bench I would remove the main board & look for bad solder joints. While I was in there I would reflow the main connections.
Here is the schematic.

[MD57md]

Yes Burn channel only

I will try it and let you know. Thanks. What do you think of the Mercury trasformer upgrades for this amp or the packages advertised by Voodoo. Will they really improve for the $ spent?

[MWJB]

Do you run it in cathode bias mode (they might call it "class A")? Cathode resistor is typically on the small side & could be cooking the tubes with too much current.

"What do you think of the Mercury trasformer upgrades for this amp or the packages advertised by Voodoo. Will they really improve for the $ spent?" They won't fix your problem, sort this first & get the amp working right.