This THD Univalve came in with a dead HV fuse, was replaced, serviced and tested all ok with the exception that the bias is way too hot for the installed 6L6GC valve. Measuring >110mA and red-plating on Hi-V setting.
On Lo-V it was ok of course, but really needed a rebias for using on our super generous UK mains supplies that can easily be 20V or more over the ‘230V’ rated.
The 300R cathode bias resistor was swapped out for a 470R version which was much more kind to the output tube and sounded no different to my ears.
Returned to customer knowing that even on Hi-V it won’t be popping anything soon.