In the chance that, hopefully, someone might have an idea of what I could try, I'm going to explain my issue and what I have tried in the past months.
My kit had been working perfectly fine for a couple of months, until suddenly it started having a noise issue on the right channel that with time became worse.
-The issue: it's a crackling/static noise that appears exclusively in the right channel, about 10 seconds after I power on my kit. It varies in intensity seemingly randomly, at times it's louder and at times it's quieter. Here's a
recording of it. The noise appears with and without a source connected to the amp (simply plugging it into a wall outlet and plugging in headphones is enough). Changing the volume with the potentiometer does not affect it in any way. RCA's being connected or not doesn't matter.
-What I have tried: I extensively chopstick tested to find any weak connection in my solder joints, and reflowed every single joint in the amplifier. I have switched around many tubes that I know worked perfectly. I have replaced the potentiometer. I have replaced the octagonal tube socket with one that makes better contact. I made sure each tube I try has clin pins and a good contact. I have added the reccommended modification with two diodes at the ground tab (it got rid of noises coming from my noisy pc). I have tried different headphones and cables. Different power cords and wall outlets. I have moved to different places of my house and different houses altogether to get rid of possible radio/wifi signals (I even tried placing my amp inside a microwave).
-The most bizzarre part: I have brought my kit to two different repairman places, on two different occasions. In both cases my amp worked flawlessly at their place (in one of the two occasions I have listened to it with my own ears and there was no noise). Upon taking my amp back home, the noise appears again.
That is when, as I said previously, I tried every wall outlet in my house, made sure there was no signal interference and brought my kit at about 4 different places to test. The noise was always there. I have made sure that my houses grounding works fine, and that I wired my transformer for 245V, which is what I read from my outlets.
As of now I am at a complete loss. I can't for the life of me figure out what could be possibly causing this, and why the issue disappears whenever I bring my kit to a professional.
If you have any thoughts or ideas about what I could do, please tell me. I just want to listen to my amp again