[Radio Wrangler]

Keeping the value of R11 at 470 Ohms for both versions, suggests that the P-Q and P-flying lead windings have the same number of turns. I wonder if someone bodged the wiring to use it for low impedance speakers?

Plenty of people have damaged Quad II transformers before now, so I expect both Ed and Mike will have the recipe for them.

The different winding sections are artfully interleaved to minimise leakage inductance and get best bandwidth, so you really do want to be using the full secondary structure as intended in the Quad II design.

The need for high bandwidth is to keep the feedback loop stable up to a high frequency where the loop gain has dropped to less than unity. This is substantially above the audio range.

David