Re: tweaking

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Nick,

On 4 Aug 00, at 11:26, Tesla list wrote:

> Original poster: "Nick Slaymaker" <nick.slaymaker-at-lineone-dot-net> 
> 
> 
> Hi Richard, All
> 
> I find this interesting because my first TC was a BT3 kit from Information
> Unlimited that has never, of course, achieved the spark length they claim.
> They make a big point that the primary tapping point is super critical.
> 
> However, I find it very boring to have to move the tapping point, then keep
> varying the toroid to ground distance to measure the max. spark; it's such
> an approximate procedure and never seems to proceed monotonically.  I would
> much prefer to read some kind of meter [as has been suggested recently on
> the list].
> 
> If I plot the [isolated] primary and secondary resonances, I deduce I need
> to tune the primary to one eighth of a primary turn!  This sensitivity
> implies that the routing of the primary tap wire is very important.  Of
> course, the tuning will be broader when streamers are streaming and the
> coils are coupled.
> 
> I'm also aware that many coilers build big coils and use a computer to
> predict the tap point and basically leave it at that [or set the primary
> small signal resonant frequency 5% lower] - it seems to work well but how do
> you know you're getting the absolute maximum?
> 
> Bob Golding and I recently fired up our big coil and got satisfying 72"
> sparks almost straight away.  We mucked about with the tuning a bit but it
> didn't seem to make much difference.
> 
> Can someone who has solved this uncertainty enlighten me?  Just how much
> tweaking do others do and what sensitivities do they notice?  Richard, I've
> just noticed you're with Freeserve so I guess you live in the UK; I'm in
> Hertfordshire.

One of the best solutions is to use a variable tuning inductor 
that can be remotely adjusted. The Tesla primary needs to be 
set to less than optimum to give the tuning inductor the range 
needed to do its job. If it is cored, the core needs to be a 
very low loss material at several hundred kHz. You won't need 
that much inductance anyway. A compressible air-cored type 
might be the best option.

Regards,
Malcolm