Re: Off-Axis Primary Inductance

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

Original poster: "Nicholas Field by way of Terry Fritz <twftesla-at-qwest-dot-net>" <nick.field-at-hvfx.co.uk>

Hi Steve

The demo you describe, removing one resonator from a twin coil and operating
it, in effect, as a single coil with 50% of inductance off axis works fine.
My Isis will throw about 6-7 feet of spark in this mode.  The only penalty
to off axis inductance is the lower k it entails, which lengthens the
notches and therefore increases gap losses.  Certainly when running Isis
single ended the rotary gap runs noticeably hotter.

For realtime tuning I would suggest the stacked primary topology, as
developed by Malcolm Watts and Richard Craven.  It offers several
advantages - lower DC resistance, because of the higher inductance/length
and lack of a conventional tapping clamp, fairly constant k factor over the
tuning range and ease of mechanical implementation (compared to some other
realtime tuning techniques).  Richard's IEE paper has a section covering it,
I think.

Safe Coiling
Nick
_______________
Nick Field, HVFX
www.hvfx.co.uk

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, July 05, 2002 6:28 AM
Subject: Off-Axis Primary Inductance


> Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<youngs-at-konnections-dot-net>
>
> Hi Coilers,
>
> For my next TC, I am thinking of having a fixed number of turns in a flat
> spiral primary, and some additional off-axis variable inductance in series
> with the primary.  The variable inductance will be used to fine tune the
> primary resonance as the coil is operating.  I am thinking the off-axis
> inductor will be two smaller spirals parallel to each other, with the
> spacing between them variable to change the mutual inductance.
>
> Can any of you help with the following question?
>
> Let's say the primary is of inductance L.  Let's say I start decreasing
the
> primary inductance a few percent at a time, and compensate for it by
adding
> off-axis inductance to maintain the same L.  About what percentage of the
> total inductance can be off-axis before coil performance noticeably
> degrades?  Anyone have some practical experience with this?
>
> I seem to remember a few years ago someone described an experiment of
> removing one secondary from a large twin coil, so the remaining coil had
> half it's primary inductance off-axis.  I believe he said the performance
> was still very good.
>
> Thanks,
> --Steve Young
>
>
>
>
>