Bugera 333xl 60htz buzz

[raynman]

Hey everyone,
I have a 333Xl combo for a little over a year now. I haven't used it very much (thanks to our lovely economy). In the last month or so I noticed on 2 occasions at rehearsal after it was on for about an hour it started to produce a 60 htz hum or buzz.
Now it does it every time I turn it on. It is proportional to the volume level. If the volume is all the way off the hum goes away with it. It does it on every channel.
The amp still amplifies and sounds normal but has this annoying buzz that won't go away.
I verified that the Melting Molex connector had been hard wired at the factory.
I swapped out all of the power tubes. (with used El34's). I swapped out the pre amp tubes one by one, I tried a different cab..no luck.

I took a look inside and didn't notice any burnt wires or components.
I checked the solder joints at the tube sockets and they seem ok.
I didn't remove any of the boards to look under them.
Does this sound familiar to anyone?

[Enzo]

Unplug the guitar from the front of the amp. Does teh amp stull hum with nothing pluged into the input?

Likewise, turn the guitar volume control to zero. Do we still get hum like that?

If we can turn down teh hum with the guitar volume control or if we can kilkl the hum by removing the guitar, then it is not the amp that is doing it.

[raynman]

The guitar volume has no effect. It buzzes without the guitar plugged in.

Turning the effects loop on with the clean channel seems to lower it a little.
Turning the effects loop on with the crunch/lead channels seems to make it worse.

The amp works and sounds exactly the same. There is just this buzz that came out of nowhere. You can drown it out as you are playing.
It gets louder with any volume increase. It goes away completley with the Master off
I turned every knob on the amp off. It still comes back as you turn up the Master volume.
Thanks for the reply

[raynman]

OK,
I decided to try using this amp one more time. The 60htz buzz came on as the amp warmed up. This is nothing new at this point. However, after playing for about 10 -15 minutes the buzzing noise went away!

I played for about an 1 1/2 or more and the buzz never came back.
It would appear that there is an intermittent connection somewhere.
Possibly a bad cap?