Hallo there, I had successfully built this wonderful amp a few years ago, it was spectacular and worked a blast! It had a small issue with one of the tubes but I put in V3 so it only affected the loop which I wasn't using.
Unfortunately even though it's a "small" tube amp it was still spectacularly loud, and I had a baby so I had to put it into storage.
Fast forward a few years, I just changed pickups in a guitar and want to hear it played through a proper tube amp so I pull it out of storage and plug it in.
For a whole 5 minutes it works spectacularly well on both channels with and without boost, oddly enough even the loop works (with a little noise).
The I tap one of the knobs and it makes a dust crackle/transient sound and the Ammp just looses it, it falls into a white noise crescendo into maximum volume. I had to flick the standby. I managed to get the amp to work a few more times, but it's always crackly and if I tap the chassis I can hear it, and more often than not the transient triggers the oscillation cascade.
I haven't read up on my electronics for a while now so I'm a little rusty and don't remember the circuit particularly well, I had a spare 12AX7 and tried swapping V3 that was giving issues years ago, but it didn't change much.
Do you think this is going to be a simple fix, or am I in for a wild goose chase?