This is the last updated schematic of mine:
https://www.mediafire.com/view/r5vsj666nir2kki/TBOLT_KA2PTE_.jpg/fileSince its using an external 3KV supply, they broke the ground that the filaments were originally tied to
and inserted the "plate" meter inline to register current - actually a cathode meter. I guess for dipping purposes,
cathode current almost equals plate with the difference being grid.
Yes, the one side of the AC coming in is tied common to chassis gnd. T102 and 103 both have one
side of their primary connected to that and I suppose you could say the 2 filament windngs on T102
are "centertapped" now because they share the common gnd.
How is the ground/neutral lead connected to the branch circuit for your Thunderbolt? With the parallel connected primaries of the two lower power transformers, the primary tap on one shouldn't impact the voltage distribution across the other.
The Thunderbolt (along with the Desk KW) were designed in the days when tying ground and neutral together at individual outlets and appliances was considered acceptable. It is simple with both of them to change to a proper isolated neutral setup which is advisable to avoid issues and comply with current code.
Rodger WQ9E