I have an old 2x EL34 amp with a 400-0-400V transformer (current rating unknown) that I modded to take KT88s. It has a little meter on the front showing power tube cathode current with a 0-300mA scale. Even the EL34s could get it up to nearly full scale, but with the new tubes, when I dime it the needle just slams against the end stop. Using the original EL34 OT with an 8 ohm load on the 16 tap, I measured about 110W out before clipping got too bad. The B+ was about 550V off load, sagging to 400V at 100w out.
So I think a 200mA transformer rating could be a bit skimpy, but you probably don't need the 500-0-500.