[Arran]

Arran

Where do you see a feedback?
C14 is not a feedback, it is a filter (notice where the left end onnects other than the grid - to practically GND) and C16 is dumb tone control cap from plate to practically GND.

Mike;
  I see it now, your are right it is a tone compensation cap, it is slightly above true ground but still not a feedback loop, I must have been looking at that late at night, or I am not used to the way the Brand Z draftsmen chose to draw things. Just the same it is a bit of an unusual arrangement since there is also C17 between the plate and cathode of the 6F6 tube. Just like a Philco though, Brand Z chose to use rotary switches for what I assume are bass and treble controls, which would annoy me. I guess it was cheaper then adding a pair of pots like an RCA would have, though I'm not sure why it would be. But then again RCA and Philco liked to connect their tone controls right in the B+ circuit of the audio output tube, which is bad news if the coupling cap on a pot should short out.
Regards
Arran