Re: Off-Axis Primary Inductance

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Nick,
         Intellectual honesty impels me to mention that at least one 
other person (Mark Barton) thought of the idea independently and I 
passed it on to Richard during conversations we had prior to his 
writing the paper. I *may* have been first to implement it as an 
integral part of a working Tesla coil but it was used many decades 
ago in radio transmission gear.
     FWIW, I'd encourage its use. It's a great way to get more bang 
for buck (tubing cost-wise) in terms of primary inductance and total 
primary size.

Regards,
Malcolm

On 7 Jul 2002, at 12:49, Tesla list wrote:

> 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
> >
> >
> >
> >
> >
> 
> 
> 
>