Push-pull audio output transformers do not have the gap, because the flux due to the DC current flows in opposite directions toward both plates, thus cancelling out their respective fluxes in the core.

It is technically possible to use a power transformer as a push-pull output transformer and your calculations are basically correct for impedance, voltage, etc. The HV output windings of most power transformers are usually split so, you could use the HV windings for the plates and the filament windings for the speaker. But, again, it cannot be used in a single-ended application.

Furthermore, power transformers are designed for efficient power transfer at 50/60 Hz without regard to frequency response. Audio transformers are designed specifically for a wide (audio) bandwidth. You might get good bass with a power transformer as an output transformer, but that’s about it.

Bottom line: you really need a single-ended audio output transformer designed for the tube you plan on using and the power level you plan on producing.

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The secondary, where the speaker is connected, would be the 6v or 12v winding.

I lost my tube manual (tossed it) long ago. But from memory, I’d use 6L6s for the drivers, they should still be available, and have a lot of power.

How well will this work? Don’t know. give it a try.

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