harddriver wrote: ↑Sat Jul 30, 2022 8:28 pm
You said you live near a transmitting tower, so the variac could be inducting the RF and or your V1 preamp tubes can also do the same thing if it not a mechanical plate issue with the preamp tubes. If it is a indeed electrical/static or RF look for inductance sources.
Maybe try the amp again without the variac first see if the noise leaves or lessens. Then you have to try preamp tubes one at a time.
Alot of people can get transient Radio waves inducted through the guitar pickup while connected to the amp because it become like a big antenna.
Is the noise bad I didn't her anything on you recordings? Has it always been there since you fired the amp up or did it just start?
I had a power supply for rack effects unit that my brother laid right next to the channel footswitch and he kep bitching that my amp I built him had gotten noisey. So I dropped by and asked why he has this power supply next to the footswitch that switch the input of the amp from 4th extra gain stage to 3 gain stages. That power supply was inducing the noise.... I about threw it into the next room and walla the amp was quiet as a mouse again.
The RF noise I've had here is constant though. This noise is directly tied to what notes you play, so that leads me to think it's just an issue in the amp.. but I'm open to consider anything to try to get rid of it.
Here's the list of things I tried and the noise remained:
Rolled all pre-amp tubes out one at a time.
Swapped out both power tubes.
Dialed the variac back up from 70VAC to 100VAC (noise got louder directly proportional to the amp getting louder)
Switch off effects pedals one at a time.
Remove all pedals from signal chain and plug guitar straight into amp.
Tried a different guitar.
The noise is in the recordings posted in this thread - I was working very diligently with post EQ to dial it out. That's when I realized I had an amp issue, not an EQ issue.
It's really deceiving because you don't hear it when 1) playing chords 2) playing notes below middle C 3) playing notes in the upper register.
You only hear it when playing single note passages in the middle register. That's when it really comes out.
Your comments made me think of a couple things I have yet to try, but probably should have thought of:
Remove the variac and plug the amp directly into my filtered power supply.
Secure the two unused power tube hold-down springs to stop vibration.