At one time (some 30 years ago) there was a company in the UK called Codar, who
made coil stock like B & W. they did move to a higher temperature material than
polystyrene - from memory, I think it was ABS, but I'm not totally sure of that.
At the kW level, I'm a bit dubious about the old polystyrene rod supported coil
stock: there's a lot of amps involved, and even if you follow Rich's advice and
provide cooling air, I think you could be pushing it. You need something like 12
AWG anyway at LF and thicker at HF. Antenna Tuner coils can run with quite high
working Q's, depending on the circuit configuration, and that can push the
heating. I use 2.5 inch diameter ceramic formers, although fibreglas works well.
Alternatively, a self supporting coil for the higher bands, wound with 1/8 inch
diameter tube. Even with ceramic coil forms, I think it's worthwhile proving
cooling for the tank circuit with a small fan.
Provided you can drill mounting holes, glass jars shouldn't be too bad for a
heat resistant low loss form. You are supposed to be able to cut glass under
water with scissors and drill it under water with a masonry drill - neither of
which I have ever tried!
73
Peter G3RZP
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