Just had one of these lovely old amps across the bench, and was extremely surprised to see a plate voltage of 730 on the two 6CA7 / EL34 output pentodes. That is some serious HT, and I'm sure rather higher than I remember seeing typically on any similar amps. The problem was low distorted audio, and was down to an O/C screen (G2) feed resistor. Full normal operation was restored once this had been replaced. G2 volts were around 360 when it was running normally. The bias was about -36v. I actually looked this configuration up, and it just falls within the maximum specs for those tubes, which are quoted at 800v on-load plate voltage max. At this level of plate, G2 and bias, the quoted max output is 100 watts. That's pretty good going from a single pair. Most amps from that era used two pair to get that sort of power.
I guess the name "Sixty Five" relates to this amp's claimed output power, but even that is PDG from a single pair, given that most amps of a similar configuration are typically only capable of 30 watts or so.
The output tubes that are in it look quite old, but they are delivering the goods, and are pretty reasonably balanced, so I am reluctant to recommend replacement as a standard 'service' option whilst it's in, given the dubious quality and reliability of many tubes these days, even when running at relatively low levels of plate voltage up to say 500v. Anybody know much about these amps ? Not terribly common this side of the pond - or at least I've not had the pleasure of seeing many from this manufacturer over the years ...
Arfa