Another question: are the OPTs autoformers or the more usual type with separate windings?
The OPTs are conventional. That's one reason I wanted new transformers - they can be rated to have a large DC voltage difference between primary and secondary. This allows the primary to be returned to the cathode of the output tube without requiring separate power supplies for each channel; eventually I hope to take advantage of that to get a new power transformer which we will be able to sell on its own. All of these things are potentially slight cost reductions.
The OPT can be wired for 2, 4, 8, or 16 ohms when used in the Stereomour; it will eventually be used in the SEX amp as well where it will do 4, 8, 16, or 32 ohm loads. Incidentally, if anyone needs switchable output impedances, the most practical scheme requires two DPDT switches per transformer. They may have to go on a board below the OPT - haven't tried to make a layout for that yet but I'll eventually want this feature on my own amps!
