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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: Tuesday, March 03, 1998 8:53 AM
To: Tesla List
Subject: Re: PVC, Re. Bert's response on Pyrex
Tesla List wrote:
>
> ----------
> From: Eleanor Flood [SMTP:eflood-at-bellsouth-dot-net]
> Sent: Wednesday, January 14, 1998 6:10 PM
> To: Tesla List
> Subject: PVC, Re. Bert's response on Pyrex
>
> Tesla List wrote:
>
> 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 --
>
> We are now using afore mentioned coated cardboard tubing for secondary
> coil. Planning a PVC one shortly. Note a reference to proper
> pre-treatment. Please, how?
> Plan to make coil as open air as possible by cutting slots lengthwise in
> PVC about 1/4' apart, this is just a thought, would it be worth the
> trouble?
> Any advise on use of PVC in this manner would be appreciated.
> Thanks much.
> H & E
Harold & Eleanor,
Welcome aboard! The funet site at
ftp://nic.funet.fi/pub/sci/electrical/tesla/
has a file authored by Richard Quick containing both text and diagrams
of coilform preparation - download coilbld.zip for details.
To summarize, PVC while being an excellent insulator when dry, also
tends to absorb water out of the atmosphere. Pretreatment consists of
drying the coilform either via heatlamps, or if a small coilform, in an
oven to drive out the moisture, then sealing it with a coat or two of
oil-based clear gloss polyurethane finish. (BTW, this will also work
with simple cardboard coilforms, but the voltage standoff capability is
not as great as for PVC).
Pretreatment is not necessary if you use a polystyrene, polycarbonate,
or acrylic coilform. Cutting 1/4" slots is not necessary, and may
actually limit your coil's capability to handle very high output
voltages. Leave the coilform intact - the losses from the PVC are
minimal and you need the insulating properties that a continuous
coilform provides.
Safe coilin' to you!
-- Bert --