BFDR Volume Loss

[Powertwang]

My amp AB763 DR has developed a bizarre problem wherein it plays great for ten minutes or so and then just has its volume drop down to zero, usually swelling back up to normal within a moment or two. The dropoff is gradual and usually takes 5-10 seconds to go from normal to 0, then swells back much more quickly. Sometimes it takes a few minutes for it to come back and sometime it does so much more quickly.

I've tried swapping out power tubes and the rectifier and, so far, have done preamp tube one, stopping to write this post and then I'll continue on down the line.

I'm pretty sure the amp's been capped in the last few years (easy enough to figure out, I know, but I haven't had time to open 'er up and see and I honestly can't remember - perhaps a sign I have too many amps) and when it's at volume it sounds fantastic.

Any guesses as to what's the issue?

Thanks,

John

[Powertwang]

Orange Whip? Orange Whip? Orange Whip? Anybody...?

[zenas]

May just be a bad solder joint, loose or dirty socket, or a tube acting up.
Place to start anyway and have a look at those caps.

[pdf64]

Fade out/in are often caused by an intermittant fault in a tube heater circuit, eg dry joint on the tube socket terminal, poor contact on tube socket.
Pete.

[schmidlin]

Originally Posted by pdf64

Fade out/in are often caused by an intermittant fault in a tube heater circuit, eg dry joint on the tube socket terminal, poor contact on tube socket.
Pete.

+1. Look for a bad solder joint on your heaters circuit and/or retension your sockets. If you have a friend handy, have them gently push/pull on your tubes as you play and you can localize the problem.

Me? I'm in the mood for a smilie:

[slider313]

Try a new 12at7 in your phase inverter.