Quote Originally Posted by DrNomis_44 View Post
... and the first thing I've noticed is that both of the Triodes in the 12AX7 tube (V1A and V1B) are wired-up with the plate/anodes going directly to the +HT supply, which I'm guessing is maybe at anywhere from +125V to +150V, given that there's a 22uF/160V cap (C8) going to ground that's acting as a supply bypass cap.
But C139 before that (and before some resistors giving a 1.1k overall resistance, and so C139 will be seeing a higher voltage than C8) is only rated at 100V, so it's more likely to be 60-80v. Still a lot better than some designs using maybe just 12v. It would have been jolly useful if they'd listed the voltages on the schematic!