So I decided to breadboard the "Musicians Amplifier" because I had all the components.
https://www.google.com/url?sa=t&source= ... 4sADn0VS0QIt's a very basic, "unimproved" Williamson circuit. I substituted 1625's and 12SN7's because I had the 1625's and they are 12v filaments. The original design calles for a Peerless S-265-Q. I have a pair of Pacific Transformer Peerless 16309 clones made for a Heathkit W5. My understanding is that they are electrically similar, certainly 10K P-P.
Everything was according to the schematic, within 10 percent. I got oscillation for days. And no, it wasn't phase because I reversed the OPT leads and the problem remained. I think I had the phase right to begin with.
So I'm asking the old hands--what happened? RF? Lousy breadboard wiring with no shielding? OPT not within spec? I'm just curious because I think it would sound lovely but I can't tell!