Peavey 6505+ heater voltage

[firemedic]

Howdy all,
I've got a Peavey 6505+ head on the dusty bench. The owner said the volume dropped out during a gig. I can't seem to duplicate the problem; it is a MONSTER.
While I checked the voltages I found that the heaters show 5.58 VAC. The disconnected filament leads have 6.6 VAC.
I know a slightly lowered filament voltage can be good for the tube, but is 5.58V too low?

[PRR]

5.58V is not the problem.

A funky connection giving 5.58V on Thursdays and 3.45V on Saturdays could be the problem.

Bright light, close inspection, chopstick.

[silverfox]

Not sure if this model uses the Molex connector to bring the heater voltage to the output board, if so, check the Molex connector for an over heated pin. This is the symptom. Look for a change in resistance of the 100 ohm resistors that create an artificial ground for the heaters. Unfortunately the components are likely mounted on the side you can't see and the output board is riveted to the chassis. If you end up drilling the rivets out, don't make the same mistake I did and think that replacing the rivets with screws will be a good solution for future ease of repair. The output tubes won't seat in the sockets with screws installed.

I spliced a separate tap to the power tubes and fused it with, I think it was a 5 amp fuse and then put a 4 amp fuse in the original heater fuse block on the main board.

silverfox.

[firemedic]

Thanks guys, I'm moving super slow on this since it's been a while and got too much going on. Will post with results.
It's weird trying to find a problem that may or may not actually exist. I suspect it is a Chinese made model; the PCB has 2009 written on it, and the kid got it for pretty cheap. So I did the standard contact cleaner spray-down of the tube sockets & jacks.

The owner said that he changed the output impedance while the amp was still on, and that may have something to do with it. I know that's not the nicest thing to do to an amp but the switch looks pretty robust, and somehow I'm not thinking that hurt it.

[firemedic]

Well after repeated voltage tests, the filaments still show a reliable 5.58VAC. Chopstick didn't reveal any looseness, this amp is pretty well put together.
Since the amp sounds good, all the pots do what they seem to be there for, and it is VERY LOUD, I decided not to fix what doesn't seem to be broken. Wrapped it up, gave it back to the 18yo owner after having sprayed electronic cleaner in the requisite orifices. If it happens again, get back to me.
I still feel the low filament voltage may cause issues but that may be what the designers intended. Who knows.