Re: "best" former material?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Ray von Postel by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <vonpostel-at-prodigy-dot-net>
> 
> John:
> Thank you.  The information is helpful.
> 
> > > John:
> > >  What is it about the materials you mentioned that make them suitable for
> > > coil
> > >  secondary
> > >  formers?  Is it their dielectric constant, lack of water absorption, or
> > what?
> >
> > Ray,
> >
> > I mentioned Polystyrene, polypropylene and polyethylene for their
> > low dielectric loss at TC frequencies.
> 
> Isn't this the same as saying that from the standpoint of dielectric loss
> at the operating frequency, we could just as well go back to cardboard
covered
> with shellac?  After all, it has low dielectric loss at the low operating
> frequencies
> of Tesla coils.

	The measured unloaded Q of several of my small coils (3.15" dia x 14"
long) measures about 350 at 300 kHz. They are wound on dried and
shellacked (is that a word?) cardboard forms.  Bigger coils would
obviously have much higher Q.  In any case, the loaded Q is so much
lower that I can't see where losses in the from make ANY difference in
performance.  PVC pipe is nice and round and easily available.......

	The influence of the wire insulation on Q isn't often discussed here,
but there is a lot more capacitance turn to turn than there is between
the form and the wire, the insulation losses should dominate.  I
maintain they're negligible and that the form is also unimportant from
the standpoint of loss.  Mechanical considerations are far more
important.

Ed