The heart of the circuit is a ferrite-core flyback transformer that you can find in an old black-white TV or a malfunctioned monochrome monitor. Even though color TV and monitors have stronger flybacks, their secondaries contain additional windings and built in diodes usually whole coated with plastic that makes them hard to deal with and just because the diodes cause inconsistency on output voltage and voltage multipliers formed with capacitors and these diodes create dangerous voltage + current + frequency combinations I do not recommend this ones at the beginning. Find the simplest, single wound secondary transformer. Check out if it’s secondary is ok with an analog multimeter. If there is a resistance (about a few hundred ohms) then you may think it is not burned (yet)
Second step is the removal of the primary windings. An old but sharp enough knife would do this so quick; just cut them and clean the winding area.
Now you only have the secondary, although it looks innocent, is capable to produce thousands of volts if you wind 5-6 turns of wire on core and then connect and disconnect it to the power supply rapidly to watch the secondary convert your high current / low voltage input to low current / high voltage output. There’s no need to remind you not to touch secondary terminals while doing this. Otherwise you’ll get nasty shocks on your fingertips as a natural warning
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