IRF540Z single transistor RF induction heater

Using just one IRF540Z transistor, you can assemble a high-frequency generator that can heat thin metal to red heat.

Coil L1 has 6 turns of approximately 1.5mm diameter wire with a coil diameter of 20mm. Coil L2 has 14 turns of 1.5mm diameter wire with a coil diameter of 4mm. The IRF540Z transistor, type IRF540, may not work properly; it should be marked with a Z as it handles twice the current. Capacitor C1 should be a high voltage capacitor and can handle a lot of RF power. Capacitor C3 is made up of three 470pF capacitors. These capacitors will also transfer a lot of power and will get hot, so I built it from three parts. The oscillator is tuned with a variable capacitor, it also needs to be able to handle the power and not fail due to high frequency sparking. I used a variable capacitor from an old vacuum tube radio; its capacitance is somewhere between 15 and 150pF, but I can't say for sure. A 1W zener diode, transistor should be mounted on a heatsink. The power supply must be rated for at least 5 A and 9 V.

Setting up the generator. Set trimpot R2 to the middle position and apply power. The current draw should be approximately 250 mA. By adjusting the capacitance of the variable capacitor, achieve a current draw of approximately 1.8 amps. Also adjust the resistance of the trimpot. Hold a fluorescent lamp close to coil L1; it should glow in your hand. Take half of a blade and insert it into coil L1. The blade should instantly become red-hot, and the current draw will be approximately 4 amps.

Next to the L1 coil, a high-frequency probe with an LED and two diodes should glow brightly.

I connected an antenna with a 10-watt incandescent lamp to this generator. The lamp glowed brightly, but the frequency would fluctuate and drift. This is an unstable generator and is not suitable for a radio transmitter.