Ampeg SVT4Pro Repair Possible?

[xray]

I bought this used from a reputable musician and it's finally starting to fade. The other night the main channel started to fade volume wise in and out. I switched over to one of single amps instead of the center bridge it performed fine the rest of the night.

Once I got home I checked the tubes - not much else to jiggle and shake in there. Anyway, are these amps repairable?

One thing that I thought was peculiar was it use to whine (like a cap charging up)during the first 30 sec of warm up. Was this normal or a potential problem?

 

[JimmyM]

I don't know much about the mechanics of them, but I do know they're reparable. If both power amps work separately but not together, sounds to me like you could rule out the easy fixes (bad tube or corrosion in the effects loop jacks), but I'd check them first anyway. After that, you'd need to take it into a tech. Hopefully it's not too serious.

EDIT: I wonder if that could have happened because of weak power at the gig? That's a VERY high wattage amp bridged, and it's possible weak power caused it to fade, while running it in a lower power situation was fine. Honestly, if you don't need it bridged, I see no reason to run it bridged.

 

[Jerrold Tiers]

Both the single bridged output AND the separate ones use the same power amps. Bridge uses both, and they are usable separately.

SO if the bridge mode fades in and out, either it is some sort of mains power issue, or it can probably be traced down to just a few parts. There is one op-amp, and two resistors, plus part of a switch..... THAT is what is used in bridge but NOT when running the amps separately, and from your description, those parts are the most likely to be responsible..

I suspect that contact cleaner on the switch is quite likely to fix the problem.