Hello all!

A couple months ago I finally upgraded to a tube amp and bought an used older model Peavey Valveking 1x12. It's been a solid little amp so far until just recently. Last time I turned it on it worked fine for about 5-10 minutes, then all of a sudden let out a horribly loud feedbackish noise that wouldn't stop until I turned the amp off (it sounded similar to when you try to plug in a guitar to an amp that's already on, but louder). I let it cool down and tried it again later that day and the next day with identical results. I've tried using different guitars and cables as well, neither make a difference. I haven't replaced the tubes yet since buying it, so I'm hoping it just needs new tubes (?), but I thought I'd check here before shelling out for that or taking it to a tech. Any advice or help would be greatly appreciated! Thanks!
I have no idea what would cause that, all I can say is take it to a tech.
Hmmm...I wonder what this button does...
I had the same problem with my VK 100w head, and it turns out that one of the preamp tubes had gone microphonic.

Search for microphonic tube on YouTube and there are some videos that demonstrate it's sound.
Thanks for the reply! That could very well be it, though the noise from my amp is much louder than anything I heard in the youtube videos. I'll take a look at the tubes when I get home tonight and see if I can isolate one as the problem. Hopefully it just needs new tubes!
It sounds like a 12ax7 has went bad
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
I also vote bad toob. Sounds like a good time to pop some fresh ones in.
Quote by Invader Jim
The questions people ask here makes me wonder how the TS's dress themselves in the morning and can shower without drowning...
My VK112 has the exact issue. It's not a tube, I tested that. I did a full power and preamp tube swap and it still was there. Does it only show up at loud volumes? Mine won't reproduce the issue when played at bedroom volumes.

I'm not sure how long it has had the issue because I only found out about it when I tried to sell it and the guy tried to gig with it. I never played with volume >1. I'm guessing it had the issue when I bought it...

Anyway, point is, it's nice to know that I'm not the only one. I'm going to open mine up soon (maybe tomorrow) and see if anything is obviously wrong. Unfortunately I can't test it at home because I moved to an apartment shortly after I learned of the issue (since it has to be loud to cause the issue). I'll let you know if I find out anything.