RE: Model T First Light

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

Original poster: "David Kyle by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-kyleusa-dot-com>

Hi Bart,

Thank you for the feedback. I had not made the connection regarding a
helix primary diameter and Coupling Coefficient but of course now that
you mention it, it is so obvious. I am kicking myself for not seeing
that before. This is a learn as you go hobby and it sure helps to have a
few masters around to show the way.

I have been reading up on theory in the archives, what a treasure trove,
and I came across some posts regarding optimal Coupling Coefficient (k).
As I understand it between 0.15 - 0.28 k is considered optimal although
it is possible to operate outside those values and many do. Are these
values still considered the norm?

So then I jump to what value would favor a small coil and what might
favor a larger one. Logically I would infer a smaller coil might benefit
from a higher k since it needs maximal energy transfer and being low
power is less likely to be plagued with racing arcs and other symptoms
of over coupling. Where as a larger coil with a big power supply might
require a smaller k to avoid the pitfalls of over coupling. What part
might the coils frequency play in this?

All, please feel free to comment if I have this all wrong.

Dave

=========================================
Dave Kyle
Austin, TX USA
Email: dave-at-kyleusa-dot-com


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com] 
Sent: Friday, March 15, 2002 7:31 AM
To: tesla-at-pupman-dot-com
Subject: Re: Model T First Light

Original poster: "Barton B. Anderson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi David,

Great to hear the smaller caps are working!

Regarding helix and spiral:
When you run the spiral, check the coupling. When you run the helix,
check
the coupling. If you
don't increase the inner diameter of the helix, K is going to climb way
up.
You need to adjust
the diameter to get the coupling back down. Once you adjust coupling,
you'll much fewer turns,
but also, you'll see just how wide that helix needs to be (you may not
like
it).

The number of turns from spiral to helix is large in your case because
the
new cap is now
"really small" and your making up for this in more inductance. The
number
of turns between
helix and spiral (not changing coupling via diameter) will is dependent
on
frequency and
primary cap size. Once you adjust coupling, you'll have much much fewer
turns (actually, you'll
probalby end up less than a spiral because the helix will need to be
quite
wide - try it,
you'll see what I mean).

My preference is a spiral. A spiral will induce the secondary just as
well
as a helix as far as
coupling is concerned. Might as well build a simple spiral and keep the
primary as far away
from the spark as possible.

Take care,
Bart

BTW, updated JavaTC to version 9.1 to repair an issue with primary to
secondary height which
John Corture made me aware of (it's good for 4 inch adjustments above
and
below the secondary,
but falls off with values beyond this). May need to reload the browser.