It would be interesting to know the phasing of the
transformer windings.

Since it's voltage fed and there is no output inductor
I would have guessed it was a ZVS flyback supply with
active recovery of the leakage inductance energy. A
flyback is a constant power output topology by nature,
so it's a natural for powering a magnetron. But the
waveform in the pdf concering the oven looks like a
forward converter. Maybe it's the result of the active
clamp?

I've designed flyback converters with outputs of a couple
KW for TWT tubes but they were hard switched with multiple
rectified outputs on the transformer stacked series to
reduce the voltage stress. At low output voltages a flyback
is unsuitable for much power because of the high peak current
developed in the rectifiers and switches.

Sorry to babble on about this but I found the oven circuit
fascinating. The white goods guys are very clever.

I hope you can get it working as a power supply for your
amplifier.