[Synchrodyne]

Thanks for that clarification.

The output from the anode of V10 goes to two places. One is the output P2 pin 4. The other is via V11 cathode follower (non-inverting) to the second volume control, thence to the treble control and V13 (inverting) and on to the output P2 pin 3.

The outputs P2 pin 4 and P2 pin 3 are in antiphase, and so nominally at least suitable for feeding a push-pull output amplifier. But they are not necessarily “equal but opposite”, as one is unmodified in frequency response and fixed in level, whereas the other is modified in frequency response (according to the treble control setting) and level (according to the volume control setting).

Asymmetric inputs to a push-pull stage would I think, be very unusual. It was not unknown because it happens in orthogonal amplifiers (which idea I think post-dated the MC unit). But it is difficult to fathom why it might have been done that way. If it was the original form, then presumably MC had a reason for it, obscure as it may be.

It does seem highly likely that the output of V12 originally went to P2 pin 3. If not, then this output would have had diminished bass. The treble tone control network (C80, R14 and VR1) would act as a first order high-pass filter. (It would have to, to ensure that VR1 adjusted the treble level with but minor effect on the bass.)


Cheers,