On 7/23/2012 4:38 PM, Gudguyham@aol.com wrote:
> Other than ceramic, can anything else be used as a coil form? Heathkit
> used a fiberglass form in the SB-220. At least I think it was fiberglass.
> Seems to have worked OK. Dentron used what looks to be some type of
> phenolic material. Not really sure what it was. Anything out there that
> can be
> used that does not cost an arm and a leg? I am looking to make a coil for
> RF about 1 1/2" to 1 3/4" dia about 6" long. Not to be used for plate
> chokes. Lou
> ____________________
To me an air wound coil is not left on the form, and many not even be
wound on a form. I say that as I used to wind (by hand) both pancake
and solenoid air core coils to handle up to 30 or 40 Kw. I did wind
coils for 125 Kw and up, but those were so large they were usually wound
on pipes of various sizes and then slid off. They were heavy enough we
had to insert ceramic spacers between the turns to keep the turn spacing
uniform.
With 1/8" and 3/16ths inch tubing we'd stick poly styrene strips on a
piece of pipe, heat the tubing and wind it under tension. The hot
tubing would sink about half way into the strips. Often it'd take some
one with a small torch to heat the tubing and it was not uncommon to put
the strips into slots milled into the pipe.The milling had to be pretty
smooth to slide the whole coil off the end of the pipe with the milled
slots. If the surface was rough the strips and hence the coil would just
become part of the pipe. One thing that helped was to put a thin layer
of DC4 compound in the slots so over heated plastic would not bond to it.
BTW these looked very much like B&W coil stock if done correctly.
73
Roger (K8RI)
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