Let me clarify the circuit: The negative feedback from the
output-transformer secondary goes to the stage that precedes the phase
splitter, in the usual way. The positive feedback that originates at a
6V6 grid goes to the stage that precedes the stage where the negative
feedback is applied. The loops are not nested. This is why I mentioned
that the positive feedback applies a somewhat distorted signal, since
that signal is taken from within the negative-feedback loop but
applied outside it.

Weird, huh?

Brian