On removing the chassis I noted the PSU 10 Ohm resistor was on the bottom of the case.
Seems it had soldered itself. The resistor was still usable - although I did change it.
I think this is the culprit :-
6BQ5 with hole blown in the anode a.jpg- (398.87 KiB) Downloaded 2255 times
Opening up the Vavle we see the flash-over occurred from the Cathode to the Anode taking out grids on the way.
- 6BQ5 with hole blown in the anode a.jpg
- (398.87 KiB) Downloaded 2255 times
This AC30 does not have a 500mA fuse in the HT.
All is now well again. Been on soak test for hours.
Not sure if the valve glass fractured first. Current must have been there for a while to de solder the resistor.
So on re-fitting the fuse I have not wrapped the resistor ends around the tags - seems we need a fuse sometimes.
SJB