beefed up champ clone

[tubby]

I'm planning to do a beefed up Champ circuit, single-ended, adjustable cathode-bias which will take everything from 6V6 to KT88. B+ around 400V.

I'm not really sure about the OT's impedance on the power tube side. I understand a vintage champ uses around 5k?
I'm aware that I'll have to compromise when I want to use different power tubes. Any recommendations as to the OT's impedance?

Thanks!

[stokes]

Something in the area of a 5k primary should be okay,just get one that will handle more power.Make sure the adjustable cathode resistor is hefty enough as well.I have a 500ohm 25w in one of mine.