From the "4/69" factory B-15N service manual:
OT-214, 6.5K primary, 8, 16 ohm secondary, 290 ohms pri. DCR, 1, 1,4 ohm secondary, stock # 8950-012
6L6GC outputs: Ep+450VDC, Eg2+445VDC, Eg1-50VDC (fixed bias model, best I've got)
This one has the EQ after the 2nd stage - all 6SL7 signal level tubes.
And I've got one of these myself and it sounds really great - wonderful bass from the 15" JBL and actually nice, in a boomy way, with my '60 Strat. I'm not sure that cathode bias would improve this but who knows?
PI is an "anode follower" driven from unequal divider resistors.
And despite what you may have read elsewhere the Ampeg, of Linden, NJ, rated these beasts at "70W peak, 30W RMS."