1st post. How to find diy voltage conversion to 240 volts

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Hi,
this must be a real newbie type question as all the YouTube videos I've watched on alternative electrical production never mention how to take the voltage coming out of the device and make it 240 volt.
I'm very mechanical minded being that I was an auto mechanic for many years and have a reasonable understanding of electrics and magnets and am currently building a magnet motor.

During my research I came across some amazing ( and stunningly built) inventions. One so simple to build and cheap and puts out 500 volts. It was solid state as well. Can't remember the name but a bunch of coils down each side of another bunch and some simple electronics to randomly fluctuate the current thru a bank of resistors the current in 2 sets of the windings causing the magnetics to wobble in the third set, ie the output coils. But no explanation anywhere I look on a simple way to convert a voltage that most likely fluctuates up to 500volts. I understand transformers but they general convert a fixed output to a new fixed output.

Not something that converts 300 - 500 volts to fixed 240 .output.

Be very great full if someone can point me to a video or even a relevant search term to use here or in google. If I put any phrase that has volts and convert in it I just get links on over the counter converters for fixed voltage ie 240 to 120 etc.

Thanks in advance
Logan