Liverpool 60Hz Hum - Fixed!

[bcmatt]

I was noticing the last few weeks that I had a bit of hum on my Liverpool. I usually don't stand close enough to the amp that I'd really notice... because when I get to close that's when my guitar usually starts making the amp hum anyways. But the drummer was complaining about the noise in his in-ears, so I thought I''d try to figure it out. I realized it was sort of a lower Bb note that was not affected at all by the amp's gain knob. The VVR control would bring the volume up or down.
the problem is, I do switch things up on this amp from time to time. I had switched back the 5.2K primaries about a month ago.

So in my trying to trace down the source of this hum, I reversed a couple of my previous mods that I don't really like:
I removed a gain boost switch and re-installed the stock bright switch (was hardwired to the highest (500pf) setting.
I also tried swapping out the EL84s. I switched back to the 6.6K primary. (I think I actually do prefer the 5.2K in the end). I was chop-sticking around a bunch today trying to find anything that affected it and I was about to give up.

Then I figured I would try removing preamp tubes one at a time. It remained if I removed V1 (makes sense since gain knob does not affect it). But, removing either V2 or V3 made it go away... so it must be created around V2. I think this means it is probably V2 itself, because as soon as I swapped V2 with the PI, it went away. So, I think something happened to that Tung-sol 12ax7 that made it no longer work well in V2. It seems to be fine enough for the PI though. We'll see how it plays tomorrow.

Anyways, I just wish it occurred to me to actually try swapping tubes before spending so much time soldering and rewiring over the last few days. I could have solved all this without even taking the chassis out of the cab.

[ampbldr2]

I have a rocket that was giving me hum noises recently that I had not heard before and narrowed it down to V2 as well.
V2 was a new Mullard CV4004 short plate so I took what ever I had lying around which was JJ and so far it is quieter.
I think I am due for a new set of output and rectifier tubes in my rocket.

Glad you got it sorted out.