[Synchrodyne]

Assuming that the input side of the power amplifier is as originally intended, then it does look as if each half of the push-pull output had its own driver stage (EF37A), and that the phase-splitter should then have been in the tuner/control unit section.

But the latter shows no apparent signs of housing a phase-splitter stage, which logically would have been the last stage in that unit. Rather that circuit appears to end with the bass and treble controls, each with its own output buffer stage, V12 for bass and V13 for treble. One would expect that the two buffer outputs would be mixed, but as it stands, they’re not. Only the treble side makes it to the apparent output, the bass side going nowhere.

I wonder if originally, both tone controls fed into V12, and V13 was the phase-splitter. Or V12, following both tone controls, fed one output directly and the other via V13, which did the inversion. The latter would explain why V13 has a cathode resistor bypass capacitor, assuming that it is original.

Is there any evidence that the tuner/control unit originally had two audio outputs? One would have come from the anode of V13, the other from either the cathode of V13, or perhaps more likely, the anode of V12.


Cheers,