Re: New Toroid

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

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

Hi Shaun,

Salad bowls and toroids are not the same. If the salad bowls are say 12"
diameter on largest edge, they
should be only a few picofarads less than the toroids "alone in the
universe" calculated capacitance
value. However, that means nothing. The salad bowls will only lightly
shield the top secondary. The
toroid will shield the secondary to a larger degree if placed in relatively
the same position.

By shielding, I mean how the toroid couples it's capacitance to the coil
and ground plane, and how the
toroid prevents corona development at the top terminal which may promote
premature breakout. It's the
capacitive affect that may be causing a problem for you. If the resonator
and toroid coupled
capacitance is different from your salad bowl setup (which it will be), the
resonant frequency between
the primary and secondary will not be in tune. You need to begin tapping
the primary at different
positions until you find the area where it's tuned.

I'm not saying this is the only possibility to your problem, but it is
definately the #1 place to start
if ther are no other apparent problems or changes to the coil. Whenever you
change "anything" in the
secondary, you should always retune the system. Some coils have a wide
window for tuning, others are
narrow.

Also, consider that the salad bowls have an edge in the center (where they
come together). This edge is
a natural breakout point and will develop corona at a lower voltage than a
radius of curvature like
toroids and spheres. Even with toroids, the breakout will occur near the
center plane of the outer
toroid surface (a few degrees above typically). Because of this and your
system (comparing salad bowl
to toroid), the toroid may need a breakout point even after it's tuned
(probably not, but something to
consider). You may want to tune with the breakout point to a ground rod for
longest arc length, and
then remove the breakout point to see how it reacts. Take your time tuning.
Fine tuning pays off.

Normally, I would be the first to say "tune it at X turns", but theres just
not enough info, especially
with the bottle caps. Trial and error works just as good in the long run.

Take care,
Bart

Tesla list wrote:

> Original poster: "Shaun R. Phelps by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <shaun-at-visorloop-dot-com>
>
> Hi.
>
> I've just completed construction of a new toroid for my coil and am having
> some problems.  Maybe someone can shed a bit of light.
>
> Input: 9KV 60mA
> Secondary: 23" * 4.5"
> Toroid: 4.5" flexible aluminum duct.  19" outside diameter, wrapped in
> aluminum foil.
> Cap: 12beer bottle  + 1 wine bottle SWC
> Primary: 1/4" copper tube, 1/2" spacing, tapped turn ~12.
>
> Previously I used two 12" salad bowls as the toroid and achieved 12" sparks.
> When I replace that toroid with the new one, I achieve no sparks.  If I use
> a breakpoint on the new toroid, I seem to get 4" sparks from that
> breakpoint.  I assume that there is simply not enough voltage present to
> break sparks from this new toroid and that is my problem.  However, I have
> read numerous posts specifying that 'you can never have too much topload.'
> I thought I would be advancing my coil by adding this new toroid and might
> see better sparks, but I see this is not the case.  I'm wondering if I
> should try and increase the input voltage or current to get the sparks I
> desire, and if I do so, can I expect better sparks from the new toroid
> compared to the salad bowls?  In other words, after increasing the input,
> might I expect bigger sparks using the new toroid or the old?  Any other
> suggestions?
>
> Thanks for any advice.
>
> Shaun.