New Ampeg V2 Troubleshooting Question

[62Gretsch]

I just bought an old V2 and have been cleaning it up. There is a pretty significant hum and I plan on replacing the 2 prong power cord in the near future and working to reduce the hum. The amp recently had two new power tubes and I swapped out the (3) 12AX7’s and the 6CG7 (reverb) tubes with the ones in my Gemini I for testing. The 6K11, 12AU7 and 12DW7 are original and I don’t have any to swap yet but everything lights up.

The more immediate problem is that after the amp is warmed up and the standby switch flipped, I get severe popping sounds even with no guitar plugged in and all volume / tone / reverb knobs turned all the way down. I found an old post on here where Enzo suggested pulling the 12AU7 and 12DW7 to see if the popping stops. I’ve pulled both and the popping stops each time. If I pull the 6CG7 the crackling continues. Also, it looks like sometime in the past the metal plate that covers the board around the 6CG7 tube has gotten very hot and scorched the metal. The power light on the front seems to work intermittently (I can’t really tie it to the popping) and the standby light comes on when the switch is thrown.

I’m pretty new to messing with tube amps and I’m not sure where to go from here. I think this tells me that the problem isn’t in the power amp section and is “upstream” of the 12DW7 tube in the preamp section and “downstream” of the 6CG7 reverb tube. I’ve turned the lights out to see if anything is arcing and didn’t see anything.

Is it worth the $70 to buy a cap kit and replace them all just in case or can I narrow it down further? Thanks!

[stokes]

If it still has the original filter caps,I would replace those before looking any further.Tubes would be the next suspect.Just because a tube lights up,doesnt mean it isnt beyond its useful life.

[Enzo]

Probably not a bad ideas to replace the caps, BUT I am not a fan of replacing parts while in the middle of fixing a problem. Old caps introduce hum, but pops and crackles come from failing caps rather than old caps no longer functioning. If one of the filters, even one at the first preamp stage, were breaking down, it would send jolts back up the B+ chain and we'd hear it no matter what. By doing mods within repairs, we have so much potential to add to the symptoms or confuse them. By fixing it first and THEN doing the mods/upgrades/recaps we know that the amp works, and then any NEW trouble is related to our upgrade work.

By pulling tubes we can localize the source of the noise to an area of the circuit. Scoping the signal path can point to the source. Wiggle each tube in its socket. Any that make noises have poor socket contact.

SInce we did not sub all the tubes, I have to point out that problems are not limited to only the tube types we happen to stock.

And remember too that any control that affects the noise is after its source.

Resistors get noisy, especially plate loads. And coupling caps break down too.

SInce the reverb is generally a side chain, it might not be surprising that it has no effect. The trouble is upstream of the other tube though.

[62Gretsch]

Enzo - Thanks for the comments. I agree that throwing too many changes into the fray can make troubleshooting nearly impossible. I decided to address the hum issues after I figured out the pops / crackle and will probably recap later on. Of course the popping has stopped since I had it apart last night - go figure. Am I correct in my thinking that it's not on the power amp side or associated with my flickering power light since I performed the tube trick and it pointed to an issue on the preamp? Thanks for the help guys!

[stokes]

"Old caps introduce hum,but pops and crackles come from failing caps rather than old caps no longer functioning." Whats the difference?They both need to be changed,right?I agree that trying to do mods while in the middle of a repair would make things more confusing,but a cap job in an older amp wouldnt be considered a mod,but would likely be a cure for the problem.The pop you get when switching the standby "on" is the cap charging.Of course if the amp continues to "pop" afterwards,there is a problem,but if it just pops when switched,that is normal.I think changing the filters would be the best start.If you still have noise problems after the caps are changed then localizing the problem as Enzo describes is the way to go.

[rf7]

Don't forget to play with the hum balance pot in the back of the amp. Usually they are not in the right spot.