abbey road d enfer said:
This is typical in most guitar amps. If the amp is not earthed and the meat-puppet killer cap disconnected, noise is dependant on the oreientation of the mains plug. That is because the capacitance between either end of the winding and the secondary/core is different.
I will take your word for it that primary wiring polarity matters for tube guitar amps but AFAIK the notorious stinger cap switch just alternated the chassis cap between line and neutral, not swapped primary polarity too (which would require a more expensive 2 pole switch, and double insulated energized wiring).
The stinger cap in old school guitar amps bootlegged a chassis ground (capacitively) from the neutral (2 wire) line cord pin. This was to shield the high impedance tube circuitry within. Obviously cap coupling chassis to the energized mains lead will have the opposite effect.
The Crown MT1000 was guilty of that. When the earth conductor's inductance was too high (long power lines), there would be a tendancy to oscillation triggered by the program's HF content. The subsequent MT1200 did not have this issue.
The driven rail power amp topology was widely used by many (most major?) amplifier companies. The main attraction is that the amplifier front end can use low voltage electronics, except for the final power devices. Back in the 90's for Peavey I even investigated, reducing this low voltage amplifier front end to a single IC, but the cost/benefit wasn't there... and the junior engineer the IC company tasked to work with us, knew less about internal IC design than I did (I had to explain to him how an OTA worked and why you could just use emitter degeneration resistors to deal with mismatched OTA LTP :
).
I am unsure that the Crown model's driven rail instability is related to mains wiring polarity, but perhaps it could be. Seems to me more like a marginally stable amplifier design. The driven rail amplifiers were always medium to low fidelity because of having to swing the transformer winding (and it's C to ground?) with the audio output, so relatively heavily compensated and slow.
Which is why I even mentioned them in this context. I have used many driven rail amps inside power modules (always mono) and never had a concern about primary wiring lead polarity, but this was a mature technology by the time I got there ('85), so perhaps already sorted and off my radar screen.
JR