Hmmm... I think you really do need a valve specialist (i.e. not me). Are the valves glowing? If not, could be the heater transformer...
Near Bognor, then. Do you go to any of the Bognor jam nights at the Royal Oak, first Thursday of the month? I went to the last one, had a gas... I'm in Selsey, as I've probably already said.
I'll email my mate and ask. Maybe drop me a line (or a ring) privately.
Steve
http://www.fivetrees.com