It is bad enough gettig primary L w/o an air gap, let alone one to allow 130-140 mA of idle current.

Put a U-L rigged 813 at ~700 volts and load it with a 5k:8 OPT and it will have a chance. 2Pi*20cps*L to equal more than 7k is not too bad. 50-60 Hy will be adequate.

I think I'll stay PP, 10k:8 is *EASY* and inexpensive( and I like PP better anyway so far ). I'm thinking a little cathode feedback from a tertiary winding, a bit of plate-to-grid with the E-Linear driver, and I'll be in good shape.

I can take a core with ~5 square inches of good Iron and get good 20-20 performance out of it to more than 60 watts. Been looking for an excuse to try the new amorphous C-Core. Probably best to R&D with M6 in the early stages.

too many cool things to do, that's for sure. The 813 ought to be good practice for a PP amp running TX pentodes at 350W/plate dissipation...
regards,
Douglas