Fender Quad reverb volume surge issue

[dotman500]

Just picked up this Fender Quad Reverb, Sounds great but i noticed the volume was not that loud. Most people say its hard to go past three on the volume knobs and i take this to 8 no problem even 10. but today i played it for a while and it all of a sudden got loud like it should and sounded way better like the watts went up to full 100 or close to it. and then went away after a minute a back to where the volume was before. this amp is the master pull out FYI. seemed after it happened if i hit the strings harder it would pop back kinda or surge so to say, i beleive it has all new tubes and the reverb was just fixed prior to ownership. also when i turned the volume up it came back to full power then when i turned it down and all the power was all gone.

[Enzo]

OK< turn the reverb down. Now play the amp until it does this. If it is already doing it, fine. Now ball up your fist and whack the top of the amp. Does that make it come back, even for a second? Does it react at all? An amp should not react to being whacked, unless you have the reverb up, then you hear reverb crash. That test exposes loose connections.

Loose connections could be failed solder joints, could be loose or oxidized tube socket pins, or a number of other things.

Also, check the speakers. First are they plugged into the MAIN speaker jack, NOT the AUX speaker jack? And to be sure, unplug the speakers and run a speaker cord from the amp chassis to some other cab. And for that matter, as it sits, grasp the speaker plug firmly and wiggle it side to side while playing. Does the sound come back even momentarily as you do that?

We could have a dirty control. Does this affect both preamp channels? I rarely use the NORMAL channel on those Fenders, but if that channel works, it tells us the problem is in the other channel. If both are affected then the problem is after the preamps.