[AI2V]

I just thought of a likely reason for the resistor- it greatly increases the current through the speaker field coil and hence it affects speaker operation. Anyone have any comments on this idea?

Since both the resistor and field coil are open and the audio output is transformer badly unbalanced, I'll be installing a PM speaker temporarily; I'm going to leave the resistor out and limit the B+ with other more practical resistors (if necessary) and see what happens.