On the rectifier thing, we need four diodes for a full bridge, since there is no certer tap to ground( the grounded CT, and two diodes is basically two out of phase half wave rectifiers ). Two diodes( one at each end ) form the curent path, one with the banded end to the filter, and the other with the un-banded end to ground. We keep the two with the unbanded ends to ground, and put a pair of vacuum diodes in place of the others, with the cathode( the hot part in a valve, banded end for SS ) to the filter. It is PN-junction noise free due to the vacuum diodes.

this made sense while I wrote it...and still when I read it. I have my fingers crossed.
regards,
Douglas