[Amps] FW: Re: tank coil heating

[Peter Chadwick]

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Chuck asks:
>What is the issue(s) with using only toroids for a tank circuit?<
One problem you can have is being able to get thick enough wire on to the core. At 1500 watts, you can have a lot of current in that coil, so you need a hefty conductor. You also need a large enough core that you can ensure it doesn't get anywhere near saturation, becasue that's real bad news. You also need to evaluate the unloaded Q of the inductor, and the losses in the core, because you will get core heating, and you need to make sure that the watts dissipated in the core aren't enough to cause heating problems. When cores get too hot (past their Curie point) the permeability drops to zero, although with dust iron, I'd expect it to literally catch fire first when the organic binder gets going. When a toroid iron dust core catches fire, it's quite spectacular (been there, done that, never again!)
Down at the 100 watt level, it's very practical, but up at 1500 watts, it's a bit more complicated, and I'd suggest you need to do a number of calculations before jumping in. The biggest problem I see is the total unwieldyness of winding really thick wire on to the core. Incidentally, you'll be stuck with using dust iron, and you need polytetrafluorethylene (trade mark name is Teflon) insulation on the wire, or in suitably thick 'cheeks' on the toroid. At the end of the day, at 1500 watts, I think that the air wound coil is rather more practical, although I'm aware that amps have been done with toroids.
Hope this helps
73
Peter G3RZP