Ah, an induction heater. The thing it seems to fail to mention (though admittedly I only skimmed through it) is that it requires HIGH FREQUENCY alternating current. You can't just plug it into the wall socket (for several reasons). Definitely a fun project though. I remember seeing an induction heater set up in much the same way that was able to turn ice cubes red-hot before they melted. Think the video's on youtube somewhere.
Thanks for sharing!
Matt
EDIT: Just read the last part more thoroughly--they are using an inverter to supply AC current at 204 kHz. They DID mention the high frequency, I just didn't read it carefully enough
By "amplifier stage" do you mean "transformer stage"? I have often heard of people using inverters or even automotive ignition coils to drive the coil. I think the webpage said an inverter was used for this particular one.
Wouldn't know where to begin guessing about the power usage.