Cathode bias in 4x6V6 output stage (caps, resistors?)

[MWJB]

"As you can tell, I'm more of a ball-park guy than a precision guy. One could crunch numbers all day long and fritter away time arguing over biasing techniques or whether the tone is better when the amp faces magnetic north or if tubes that have been dipped in chocolate sound better than those dipped in caramel. I don't really care about that. Really, I don't."

Then why ask? Threads take on a life of their own, fact of life, live with it. Whilst I'm enjoying sparring with Kleuck, if you hadn't asked...it wouldn't have happened. So you inadvertantly started a needle match, wasted whatever effort was put into the thread, and now you don't really seem to care if there is an answer...& you were making up any voltages anyway...& you refer to contributors as "trolls"...(people in glass houses & all that)...marvellous innit?

[SRT]

Really? I *wasted* effort? I got exactly what *I* wanted and asked for (the answer from Gingertube - thanks again, Ian - relationship between tube curves and Rk value). I didn't ask for anything more. That was *all* you guys.

[kleuck]

Not "that" accurate, as this calculator is intended for fixed bias amps, where the plate voltage is the "plate to ground voltage"
With a cathode biased amp, plate voltage is "Plate to cathode" voltage, so more like 395-400 volts for your amp.
And actually, the plate voltage will not be B+ minus the cathode voltage, cause you will have a voltage drop in the primary of the OT (and choke), obviously i don't know precisely what it will be, depends on the OT's quality, construction, power handling, but it can be of 10, 20 volts, more perhaps, actual plate voltage can therefore be as low as 380 volts.
The calculator gives 26 mA for 70% at 380 volts.
Almost a 12% difference, not trivial, as MWJB said before, it would be a cold bias.