Awesome! Hoped you still trawled this forum!

Actually the first thing I did was replace the tube (arguably the most obvious denomination).

I have checked over the capacitors (aesthetically, they look fine, and this thing is not that old so they shouldn’t be expected to have popped, however, the unit worked before I left it powered up for a day).

I don’t actually have a scope (I do have access to one though if worst comes to worst), but I will subject it to some multimeter testing when I get mine back.

Symptomatically speaking, it does sound like an incorrectly biased gain stage does it not? So its likely that something has gone either on the tube stage side or the opamp side. I will most probably sequentially replace the semiconductors and see what happens.

Thanks for your reply!