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So is the 100ma rating on the power trans adequate to run PP 6v6's?
Yes, but...:-) See some tube data for 6V6 and EL84 (similarly). With "standing current" of about 30-40 mA per tube, and Ua of 250-300V we can expect about 4-5 W in PP triode A class, or about double in UL. Pentode and AB class ~15W or little more. With max. power, our 60-80 mA "standing current" would rise very close to the 100mA, and better use "economical" driver tube that work with only a few mA...
Hey-Hey!!!, I think the L-C filter would gain us something, especially if a conservative rectifier was used. 400 volts @ 100 mA is 40 watts. 3A of 6.3 and 5 VAC is about 30 watts. 70VA core will have more to give the HV is full use of the heater taps is not made. It will not be all that close I suspect. Class A bias with 6V6's in U-L and using the middle taps and a 6BK7B driver pair( figure ~6 mA for that stage or so ) will give B+ of ~240VDC. No biggie.... regards, Douglas