After blowing fuses and worrying I'd ruined my old JCM 800 2204, I sent it away to get rebuilt at Flynn Amps in Glasgow.
http://www.flynnamps.co.uk/ (http://www.flynnamps.co.uk/)
No idea how much an overhaul and revalve would cost normally, but getting it done for £170 seemed ok to me. Company was great to deal with, would happilly recommend to any Scottish board members.
Now to see what it sounds like with new pre-amp tubes and after a good service... Will post an update for anyone who cares soon!
Mesa valves, all replaced. A lot brighter sounding now, plus appears to be a bit louder too. All annoying hissy noises gone ;D