[TV MAN]

I have been doing a lot of reading and continue to. I am surprised at the amount of info on this. Everything but the knobs lol ! From my experience with this, those outputs do run pretty hot. I killed a set of tubes back in the day when new old production tubes were still available, and not terribly expensive. I had a friend from ITT tech that brought a set of output tubes from his Fisher to class, and it stymied me. Those tubes glass envelopes were melted and the bakellite bases were nearly completey burned off! This was back in the mid 1980's, so at that time, our 500s were 'only' about 20 or so years old! His was a 500B. So, I know what these units are capable of.

I am somewhat in agreement to power up and test in stock form before any mods are made. This has merit, and I often do this when practical. Then, start making adjustments. I do know, however, that their stock bias setup is less than perfect, then add 50 or so years to all that - yeah. I must have the bias supply working properly before I hit those tubes with full power. I believe the bias rectifier is a problem child, so I will at least replace that before I test it. I really don't want to destroy a set of known good 7591a tubes. I am leaning toward building the IBBA, which not only sets each tubes bias and current draw but also balances each pair. I'll probably go with the Hayseed E-caps for simplicity.