Bugera 333XL popping noise

[24seven]

Hi,

I have just bought a Bugera 333XL with the 4x12 cab and have a problem out of the box. This is my first stack amp so I am wondering if I have missed something obvious.

When I power everything on it works fine for about 60 seconds. Then I get a popping noise every 10 seconds which will quicken to up to 3-4 seconds. This happens with no guitar plugged in and all settings at zero. It stops if I turn standby off.

It came with EL34's which are currently biased to about 44V (which I think is a little high - the Bugera manual provides different voltages for different tube grades and I dont know which one to use). I have plugged in the cab and set the speaker switch to 16ohm. The cab has been set to mono and a guitar cable plugged into the input (ahem).

Do any of you guys have any idea what I could be doing wrong or what could be wrong with the amp itself?

Thanks
Mike

[Enzo]

Yes, my first four guesses would be bad power tube. Turn the room light out and look closely at the power tubes in the back. Do you see any tiny flashes of light INSIDE the tubes when the noise occurs? Flashes inside tubes indicates bad tube.

Also, when it is doing this, rap on the side of each power tube with your knuckle or a [encil or something. Does that have ANY effect? The tube should not respond to the hitting at all. if it does respond, something is loose inside the tube.

Popping and crackling is usually the sign of a failing powr tube.

The tubes are only covered by the warranty for like 90 days, so don;t waste time. COntact the amp seller and tell them it pops and crackles and makes the other noises. No point in buying new tubes if the warranty will cover them.

[24seven]

Thanks very much for replying. I'll try what you suggested.