I've read of using the LarMar type with good results. Would you use a dual 100k here? I don't see anything that would stop me... although I have the urge to install some screen grid resistors. Not my amp though... he loves it as-is, just wants to knock the volume down just a few db without changing anything in the rig... including lower efficiency speakers. He said change tube or fix anything bad.
Odd rectifier... I can't recall seeing the PT secondary connected directly to a series cap set like that... two different filter values at that. Oh well, it works and I learned something new.
The yellow wire coiled and terminated in the air is the unused primary tap for 100vac... WTF??? There are plenty of unused terminals on that rectifier strip-board. I guess you can lead a horse to water but you can't make him think!
The obsessive compulsive in me wants to fix that and change those power tube sockets to a couple of new Beltons. The one on the right barely spans to catch the mounting screws... that is good enough reason to proceed right?
Also, all three preamp tubes are Mullards with RCA black plate 6L6s... Sweetness!!