Put together here a few steppers as Alternators high frequency high voltage oscillators for testing .
Using one half of them voltage range is up to 100 volts on the best one running half the stepper and 200 no load on correct wiring
So there are 3 Alternators here ...4.5 khz 5.5khz and 5.5 khz on load the wired up one gives 6.5 khz that is lighting the 240 volt bulb i found so far putting a 1 k resistor across this increases the frequency to 6.9 khz might be worth testing this with a pot .
They would be half this frequency running one side of the stepper ///there are 2 ways to double the frequency and voltage either short 2 windings from the unused side of the stepper or connect one lead of the unused side to the used side of the stepper same result it seems ...
Well mixing 1 alternator both half's frequency doubles wonder if using 2 alternators mixing the frequency does the same worth a shot also there to test Stepper motors i come across
I have used a passive frequency doubler in the past but it does drop the voltage as i recall got up to 16 khz last time i tried
Need to also look at if there are Harmonics this could be useful in this case///
They are a bit noisy for this go doing this video
youtu.be/vnGuei1zgz4