This is really a nice project that any serious electronics hobbyist should tackle, or rather not, because it’s really dangerous, uses mains voltages, and emits undue amounts of RF radiation non-complient with all common regulations.
So please, take this for educational purposes only, don’t try at home, unless you are fully qualified, and have a shielded room, with no RF leakage to the outside world.
The coil is made of about 0.3 mm copper wire (magnet wire), and resonant at pretty much exactly 250 kHz. A 2″ aluminum duct is used as terminal capacity, bent to a toroidal shape.
The circuit – it’s pretty basic. A SG3524 is used as the driver, with a 10-turn pot to adjust the frequency (to resonance). A small bit of FM (frequency modulation) can be provided from by an audio signal, fed via a pair of Cinch connector (sorry, no stereo – both channels are combined internally) – turning the solid state Tesla coil into a “plasma speaker”. You can hear the sound of your favorite song, played by hissing sparks, if you dare to hook-up you MP3 player to this apparatus (use a long cable, and an inexpensive player; don’t touch the player, when the coil is energized – you will radiate far too much RF into it!).
The SG3524 output is used to feed a gate drive transformer, which in turn drive the MOSFETs (2 pcs IRFP450, 500 V – 0.4 Ohm – 14 A). The low voltage part/driver is power by a little transformer, the IRFPs are connected directly to a DC voltage derived from the mains input, about 300 Volt (operating from 230 VAC in Europe). Don’t touch the primary winding!
Some VDRs, capacitors and diodes are used to keep transients away, and to keep it running stable.
The final device – it’s working great, but don’t have pictures at hand – will provide later! As I said, don’t try this at home, but I will gladly answer any of your questions.