Hi,
I'm new here, and have done some research on this. The circuit of the Martin 112/DeArmond R15 is basically a Fender 5e3 Tweed Delux with some pot and cap changes... and a huge OT. The schematic is available on the CD in the new Groove Tubes book - the only entry under Martin. Tonequest bought one and liked it so much that they, blueprinted it, and cloned it (their Clarksdale amp), sending the transformers to Mercury Magnetics. Mercury lists these (DE-AR-OT, DE-AR-PT) under "other transformers" (down at the bottom where Felix is walking back and forth). I ordered a set to check them out, but asked Paul for a larger PT. He suggested the FBFVL-PM, the lower voltage Vibrolux option. The Clarksdale is built with the Sozo "mustard" caps and an Eminence Wizard speaker, which they liked best. Other transformers: I believe Paul said that the primary was 6.7K making it suitable for running 6l6s/7591s (ToneQuest suggests running 6L6s with a 5AR4 in theirs for more headroom). Antique Electronic Supply has replacements made by Hammond, I believe, and Allen Amps has some made by Heyboer, both less expensive than the Mercuries.