Hey! Just bought an old Fender Bassman 100 that is in need of some adjustments. I'm not very experienced with repairing these kinds of amps, but i'm hoping on some help from some of you more experienced guys on here to at least do some diagnostics. I've added an audio sample of the sound. It is not constant, but seems to only apply to some tones and above a certain volume. At 0:39 you can hear me smack the top side of the amp and then the noise disappears. In addition I can only see a glow in two of the four tubes, perhaps this might be a part of the problem? Before you ask: Yes, I have changed every other part of my signal chain. Bass, cable and cabinet. Thanks!