Well, I changed to regulated B+ and filament supplies, so it is a fair amount of rework... It also has a HPF on one pair of outputs but that is trivial to change. Finding the old gal is the hard part...
It is not a priority for me right now, maybe when I retire in ARC ran the zener string hot so they tended to short and take out the power transistor, which was some "special" device. I am not sure what I replaced it with; about the third time it blew I got fed up, found some generic replacement, and added a series of regulators to isolate the stages and reduce the zener bias current. I think I still used the zener string, not actually sure, that was ca. 1980-something. It worked through maybe 2000 or so when I abandoned that system and put her into storage.
