Each mag has its own waveguide with a rotating antenna at the end that extends into the oven cavity. 2 of the waveguides are at the top of the cavity firing down and the third is at the bottom firing up. The HV transformer primaries are wired so that the top 2 mags fire on the positive alternation of the AC sine wave and the bottom mag fires on the negative alternation. The top 2 antennas are driven by a single timer motor with large plastic gears (complete with timing marks) so that they both are pointing the same direction at all times as they rotate. The HV transformers have tapped primaries so that the oven can operate on either 208 or 230 volts with no change in output power. Also there is a small 208-230 volt boost autotransformer that boosts the voltage for the cavity lamp, cooling blower, and antenna motors when the oven is plugged in to 208. When the microwave is first plugged in it sits for about 30 seconds to (I assume) to sense the supplied voltage and frequency so that it uses the correct taps on the 4 transformers. Oh yeah when the oven is set for less than 100% power the HV transformers are cycled on and off by 3 triacs (1 each) with arc snubbers across them and there is a relay that cuts the power to the triac/transformer circuits when the oven is off. Each mag has 2 thermal cutouts, 3 cut off the power to the respective transformer primary and the other 3 are wired in series and are connected to the logic board which makes the vacuum fluorescent display show HOT and also causes the oven to refuse to operate. There is also a thermal fuse in the oven cavity air discharge duct.
I think I have provided WAY more info than anybody wanted or needed.