Heat treating...

I may be way off line here but you should check the power rating carefully if these are hi-fi type audio amps.

My understanding is that they are not designed to handle continuous sine-wave input those sorts of power levels - only occsional transients.

Linear amplifiers that can handle 2kW continuous sine wave at MHz frequencies are the sort of thing that enthusaistic radio amateurs build using massive transformers and air-cooled valves.

Make sure the amp can deliver continuous sine wave power without overheating.

Now I'll wait for the experts.

To get 42uH in air would require between 20 to 35 turns for a reasonable sized coil. That'd give you 8 Ohms at 30kHz with no iron anywhere near it. Put 1uF of capacitance in parallel with it (series parallel stack of motor run capacitors probably) and drop the frequency to about 24kHz and the impedance goes towards infinity until you introduce a lump of metal into the coil.

Use a smaller number of turns and a larger capacitor and you can, within reason, get any size coil you want.

At that point, you probably want a hall effect current sensor, potential divider and PIC processor to measure the phase angle of the current and trim the frequency to keep the whole lot close to resonance. None of that is particularly challenging electronics or programming. I just don't know if it's a meaningful thing to attempt...

So many ideas. So little time.

Mark Rand RTFM

"Induction heating" under "Amps, Volts, and watts" at