After watching a > 2 hour recorded documentary on the Rolling Stones returned to do a little more testing. Plugged in remaining 2 valves (the EM 71 Magic Eye that had previously been removed for its own protection as was vulnerable to being knocked) and the ECC 81 (previously removed for snubber tar cleanup).
They like the other valves lit up OK, switched on and off a few times do a couple of checks, each time the valves went off when the on/off switch was switched off.
But a little later on a subsequent switch off, I noticed that the valves this time stayed lit.
Upon investigation both switch poles of the on/off are now permanently switched/made whether the switch is mechanically on or off, the switch makes a lovely solid mechanical sound when switched off/on but electrically now never switches off.
I did not believe it initially and unsoldered the switch wires to double check everything, which confirmed that the 2 mains switch poles are permanently made/shorted.
The switch had been thoroughly checked both resistance and voltage wise during the Bulgin mains plug upgrade and also rechecked all OK at the beginning of the power on tests tonight, but obviously after a short usage has now failed.
Little can do about it, the rear cover of the mains switch (integral to the volume control) is riveted on and even if I drilled the tiny rivets out, not sure if could get inside as the 4 switch contacts protrude through the body and even if could get inside probably unlikely to be repairable.
A shame, I just have to remember now to unplug the mains plug before doing any work inside (of course I would always do that anyway)
