Please do keep us posted.  A few days ago mine starting making popping noises.  It is rare (maybe twice or so when playing for 30 mnutes to an hour) and I had assumed it maybe was a tube going south.  My amp is only a few weeks old.

Guys-

Mystery over!!!  - My tech & I decided the problem had to be in the bias pot area & even before we fired it up on the bench as an afterthought I gave the two resistors from the negative bias probe a gentle yank & low & behold- one had a totally dry joint at the tube socket terminal end- in fact it popped right out with hardly any effort!  This would explain the weird bias fluctuations & noises... No disrespect to Nick & his team- this could happen to anyone's solder work- especially as the amp has been bounced around in the back of my car on gigs & not forgetting the 3000 mile journey from Malaysia to the UK!  So check for dry joints in this area if your OT makes similar 'frying & popping'  noises - it's especially vulnerable here due to the heat rising through the chassis from the O/P tubes.

I'm a very happy man again- in the nick of time too as I was about to break out the old Crate VC50 from the garage for tonight's gig! 

Mitch, glad you have a happy ending.  Mine will be as well but its gonna take a little longer, I am afraid.

My power transformer went totally ker plunk and ker pluey, bad part.  The tech said it didn't appear to have overheated, it just died.  Nik's been right on top of it and a replacement will be sent Monday.  Mystery solved, although amp is currently out of commission

...just as we were getting to know each other.