Page 524, Figs 12.30A and 12.30B, but it is not quite like either one. It is one of a huge family of Paraphase drivers. The Patents and the RDH are bullplop; real designers who had to keep it cheap and keep their job did it as in your schematic.
I suppose they saved a resistor, and I am sure Valco wanted to get as much money as they could from gretsch. I have been going through the Methodes of Exciting Push-Pull amps section of RDH4 this past couple days, I never really spent much time bothering with these since I prefer single ended amps, but its time I learn.
Page 540, section 12.10.G.2, suggests heater CT to a small bias voltage, but does not suggest the output tube cathode. (I suggest that this would be "obvious" to anybody who had spend too much time poking a meter in a tube radio.)
Well thats my problem, I have never poked about a tube radio, just amps, and none this old. No, one tube radio, a big old Hellicrafters I fixed up for a friend, it did not have a center tap on the filament supply.
Betcha it goes to the first stage cathode.
Betcha you are right, last place for it to go.
Scroll down to Gretch in the left column. They don't have your model, but the others have the same mix-n-match pieces.
Missed the Gretsch schematics when I went there somehow, but I did go through the Valco and found a couple that were close.
This is pretty close to ready to try out, just need to run a wire from the tremolo and wire the power chord and output transformer. Although I suspect it is going to need coupling caps replaced. Who ever worked on it in the past just stuck a second cap of the same value in series with the original ones. I can only assume they were dealing with the leaky caps in their own way with that, cant imagine it sounded good with its cutoff shifted up an octave.