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PVC, Re. Bert's response on Pyrex
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From: Greg Leyh [SMTP:lod-at-pacbell-dot-net]
Sent: Wednesday, March 04, 1998 4:25 PM
To: Tesla List
Subject: Re: PVC, Re. Bert's response on Pyrex
Malcolm Watts wrote:
> In the light of this response, I have a question to ask of Greg Leyh:
>
> > [snip]
> > NO! If I understand you correctly you are talking about laying the wire in
> > precut groves in the PVC, this will increase the distributed capacitance
> > and thus lower the secondary output.
> >
> > -Alfred A. Skrocki
>
> Did embedding your new secondary in resins etc have any effect on
> frequency and output and if so, by how much?
During the design phase I had predicted Fres to be 38kHz,
and it actually measures 37.92kHz, with the topload.
I consider this to be a lucky guess for the most part.
If you consider the electric fields around the coil,
they emanate outwards from the winding surface at roughly
90 deg, then slowly bend downward, raining towards the
ground. If you examine the trajectory of any one of these
emanating field lines, you can see that only a _very_ small
percentage of the trajectory goes thru the outer fiberglass
shell of the coil tower; most of it goes thru normal air.
Therefore, the 'sheet capacitance' of the secondary to
ground stores less than 1% of its energy in the fiberglass
medium, and it would be far less than that if the
fiberglass tube was on the _inside_ of the sec, where the
electric field is considerably lower.
The turn-to-turn capacitances in a coil are negligible,
as these values are small to begin with, and they must
add in series when it comes to bending the freq of the coil.
-GL