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Pyrex diss. factor




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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Saturday, February 28, 1998 10:34 PM
To:  Tesla List
Subject:  Re: Pyrex diss. factor

Tesla List wrote:
> 
> ----------
> From:  Alfred A. Skrocki [SMTP:alfred.skrocki-at-cybernetworking-dot-com]
> Sent:  Friday, February 27, 1998 1:04 AM
> To:  Tesla List
> Subject:  Re: Pyrex diss. factor
> 
> On Wednesday, February 25, 1998 1:38 PM Edward V. Phillips
> [SMTP:ed-at-alumni.caltech.edu] wrote;
> >> "Jim,
> >>
> >> I checked "Dielectric Materials and Aplications" by von Hippel:
> >> Pyrex (Corning 7060 - Soda-borosilicate) has a loss tangent of around 28
> >> in the Tesla Coil frequency range of 10^5 - 10^6 Hz. Alkali-Silica glass
> >> (12.8% Na2O, 87.2% SiO2) comes in at around 240-159 in the same
> >> frequency range, and soda-lime silicate is similar, but a bit lower for
> >> the same frequency range (140-100).
> >>
> >> Jim, I also suspect that, other than doing an actual measurement of
> >> secondary Q, you'd be hard pressed to distinguish any performance
> >> difference between these as a Tesla Coil secondary coilform.
> >>
> >> Safe coilin' to you!
> >>
> >> -- Bert --
> 
> > "
> >
> >  One big difference!  The Pyrex won't carbonize in the event
> > of breakdown, and won't be likely to crack with the heat either,
> > so it (the glass form) should be more or less indestructible.  Of
> > course, it will be pretty heavy,,,,
> >
> > Ed
> 
> Glass of all types has large R.F. absorption ie high power factor and
> as such is a poor choice for any part in a Tesla coil! The same poor
> performace yielded from salt water/bottle capacitors and glass plate
> capacitors can be expected from using glass as a secondary form! Much
> better to use PVC or better still polyethylene or the best of them all
> Teflon! Although the last one will bankrupt you for sure. Heck even well
> baked out cardboard tubing that is saturated with polyurethane and allowed
> to dry under heat is superior to glass!
> 
<SNIP>

Alfred,

Got to disagree with you a bit here, Alfred. The difference in
dielectric loss between PVC and glass is really not all that great...
and Pyrex (at about 30) is actually about 1/4 as lossy as PVC. Even soda
lime glass is only 1-2X as lossy as PVC. While using glass, or PVC for
that matter, as a dielectric in a Tesla Coil tank cap would be quite
lossy, use of this material in a coilform is a significantly different
application. PVC, although quite lossy, makes an excellent coilform due
to it's excellent insulating properties after proper pre-treatment. Its
dielectric loss properties have relatively little practical impact on
secondary Q when compared to other losses in an operating system
(streamers in particular...). 

Jim, your Pyrex coilform will work just fine.. and may actually have a
higher Q than if you wound it on PVC.

At no loss for words in Illinois...  :^)

-- Bert --