Bugera V22 clean channel going dead silent.

[olddawg]

So this is another "mechanic's car won't start problem". I've been using this amp a couple of nights a week for 3 years. The only other problem I have had is it tried to shake itself apart with loosening screws. The last 2 times I have gigged with it, about 2hrs into the night, the clean channel slowly fades out over a period of about a minute. The dirty channel works fine and the foot switch says it's switching. I get it home and cook it for days and can't get it to fail. I think what I will do this Saturday night is completely power the amp off between sets and hope for the best. BUT it would be nice to figure out what is going on. It kind of sounds like I'm losing a heater on a pre tube. Since it has the stock 3 year old Sino tubes I thought about just retubing the damn thing, but it sounds fine, isn't microphonic and I think the dirty channel just cascades another tube. I've seen some posts about switching problems with these, but not this problem. Oh... and the Enzo whack doesn't affect anything . Any Bugera servicers or bulletins out there?

[alexradium]

tubes either they work or not,maybe you have some switching problem or a resistor in the supply going bad with heat,cracked soldering.
schematic is similar to Peavey classic 20

[olddawg]

It's just damn strange that it takes 2+ hrs to happen. I hate intermittents. This may be one of those cases that I have to resolder everything and hope for the best. The schematic is available online. But if it won't enter failure mode on the bench that isn't much help. The slow fade out is a clue.

[alexradium]

It's just damn strange that it takes 2+ hrs to happen. I hate intermittents. This may be one of those cases that I have to resolder everything and hope for the best. The schematic is available online. But if it won't enter failure mode on the bench that isn't much help. The slow fade out is a clue.

try injecting a test signal and blow hot air with a heat gun on different critical areas

[olddawg]

I can do that I guess. I threw a tarp over it and ran it for a day with program music.

[Enzo]

And you can go the other way, once it starts doing it, hit the circuit with freeze spray, see if it chills back into operation.

[nickb]

You know here are only five parts that are unique to the clean channel, R76, C49, Clean Vol pot, C60 and RL1. Of those we can discount the caps as the would not cause a complete loss of signal. Of what remains, RL1 would be my first suspect or any related solder joint. I think that narrows it down quite a bit for you.

[olddawg]

You know here are only five parts that are unique to the clean channel, R76, C49, Clean Vol pot, C60 and RL1. Of those we can discount the caps as the would not cause a complete loss of signal. Of what remains, RL1 would be my first suspect or any related solder joint. I think that narrows it down quite a bit for you.

Thanks.. I'll check those. I always suspect a relay. But the failure mode is strange.... the way it will be fine for hours, then slowly fade out over 30 seconds or so. Then be dead the rest of the night.

[nickb]

it will be fine for hours, then slowly fade out over 30 seconds or so. Then be dead the rest of the night.

Are you certain it's not sneaking off to the bar when you not looking 'cos that's exactly what would happen if it were....

[olddawg]

Are you certain it's not sneaking off to the bar when you not looking 'cos that's exactly what would happen if it were....

And there's that that....