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PVC, Re. Bert's response on Pyrex
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From: Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent: Saturday, March 07, 1998 11:14 AM
To: Tesla List
Subject: Re: PVC, Re. Bert's response on Pyrex
Ed and all,
Don't know what happenned to the last part of my message - my "sent"
file is intact. Ah, the wonders of the Internet! I've included the
missing portion of the previous message below.
Ed and Alfred, sorry about my confusion on the pretreatment for Ed's
resonators. Guess I've been too close to large EM fields lately, or
maybe it's ozone overload... :^)
I fully agree that pretreated cardboard works quite well - Ed's system
is one of the best existence proofs I'm aware of! I also see no reason
to think that pyrex (other than being heavy and brittle) would not
perform as well or better for Jim Heagy. Besides, shellac, in addition
to drying faster, also smells a lot nicer than polyurethane.
-- Bert --
The missing portion of my previous post should have read as follows:
========================================================================
<SNIP>
... However, I also suspect that cardboard's voltage-standoff
and leakage current characteristics are not as good as some of the other
materials mentioned. If you saw significant performance differences, I
suspect it was due more to leakage currents than dielectric dissipation.
A portion of your [Alfred's] earlier post is repeated below:
<SNIP>
> 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>
Perhaps lossily, but certainly not leakily yours...
-- Bert --
========================================================================
Tesla List wrote:
>
> ----------
> From: Edward J. Wingate [SMTP:ewing7-at-frontiernet-dot-net]
> Sent: Friday, March 06, 1998 5:16 PM
> To: Tesla List
> Subject: Re: PVC, Re. Bert's response on Pyrex
>
> Tesla List wrote:
> >
> > ----------
> > From: Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
> > Sent: Thursday, March 05, 1998 12:50 AM
> > To: Tesla List
> > Subject: Re: PVC, Re. Bert's response on Pyrex
> >
> > Tesla List wrote:
>
> <large snip>
>
> > Alfred,
> >
> > My original reply was regarding an earlier post to answer a question
> > about Pyrex from Jim Heagy. Although my response was requoted in the
> > last post, it lost some of its context since the earlier posts were not
> > also requoted. It was the earlier posting that directly compared Pyrex,
> > PVC, and cardboard coilforms.
> >
> > However, I still stand by that post. There's a BIG difference between
> > using glass, Pyrex, or PVC as a dielectric in a tank capacitor and using
> > it as a coilform. PVC and Pyrex make excellent coilforms based more on
> > their dielectric strength and low leakage current than their dielectric
> > loss characteristics. Dielectric losses in a coilform are simply more of
> > a secondary (npi :^)) concern.
> >
> > However, the simple fact is that Pyrex, with a loss tangent of 36-40 x
> > 10^-4, has less than 1/20 the dielectric loss of PVC, at 800-1200 x
> > 10^-4. Heck, Pyrex was even used as a coilform by Breit, Tuve, and Dahl
> > for their oil-immersed 5 MV, 100 kHz coil ("High Voltage Laboratory
> > Technique", page 109, Meek and Craggs). While they probably would have
> > used PVC had it been available back then, I doubt that cardboard would
> > have worked as well as Pyrex.
> >
> > I also contend that, although you might be able to measure differences
> > in instrumented Q between identically wound coils on these materials,
> > there will be virtually NO performance difference when the sparks are a
> > flyin', since other factors (streamer losses in particular) will easily
> > drop the effective secondary Q by an order of magnitude.
> >
> > However, if you've got a leaky coilform, that's a different story. I'm
> > not disputing that you can make wooden or cardboard coilforms that will
> > work well after proper pretreatment. And for larger coils there may be
> > no other readily available, affordable alternative. Heck, Ed Wingate
> > gets great performance from large cardboard resonators with no
> > pretreatment! However, I also suspect that cardboard's voltage-standoff
> > and leakage current characteristics are not as good as some of the other
>
> Bert,
>
> I didn't snip the last paragraph. That's the way the post came off the
> list.
>
> I have to say that I definitely DO treat all of my sonotube coilforms
> before use. I first set them near a heater until I'm certain they are
> dry, and then I apply at least three coats of shellac both inside and
> out. I also make sure that the edges are well covered. After the wire is
> wound on the form I then apply another coat or two of shellac to hold it
> in place. I prefer shellac to clear polyurethene because it doesn't
> crack and peel with age as the polyurethane does. Shellac also has the
> advantage of drying faster which makes the whole job go much quicker.
>
> Ed Wingate