Fender Princeton reverb 65 reissue: buzzing and incredibly distorted sound

[Falstad]

Not sure what caused this, it just happened out of nowhere.Thing buzzes like beehive even with the volume turned to zero. The guitar sounds like some some weird alien chatter, as you can hear in the video.

Initially I thought it was a bad tube. I took a look at the diagram and found that the reverb tube wasn't glowing like the others. I ordered a replacement Fender Groove Tubes GT-12AT7 on Amazon and swapped it out. Unfortunately, the problem still persists.

I've read a good way to test the integrity of a tube is to tap it with a chopstick, none of the power/preamp tubes make any "hollow" tapping sound when tapped. Could this be a speaker cone issue? Anyone have further recommendations for troubleshooting?

[The Dude]

That could be many things. My first suspect would be a filter cap. Fender uses Illinois caps, which are known to have issues. I'd first test all of the filter caps. It could also be a bad output tube. If you have a known good set of output tubes, try substituting them and see if it solves the problem.

[Chuck H]

If the amp has been sitting a while or if it has been having this problem for a while you should start with cleaning all contacts. Jacks and tube sockets. Possibly pots. It may also be a cold solder joint. Sometimes a cold joint doesn't present before an amp is dissused for a while. So retouching solder joints with a little flux or fresh solder is something to try.

I also endorse The Dudes opinion on the IC caps.

Short of opening the amp and taking voltage measurements any attempt at repair for what I hear should start with cleaning all contacts and retouching solder contacts.

[Jon Snell]

I would suspect a screen grid resistor is open circuit, R39/40, causing 100 or 120HZ hum/buzz depending on your mains frequency.
Or a duff 6V6.

Failed smoothing capacitors will give slight hum but mainly lots of low frequency harmonics when playing.

[Falstad]

Thanks for the replies everyone, but I'm a novice and this is all Greek to me. I was hoping this might be a relatively simple fix but it's not sounding that way.

I think my best bet is to take this to someone who knows what they're doing and has the knowledge you all have. Thanks!