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>

The new caps came in and with a few modifications I got them fitted to my
battery powered Model T spark coil powered Tesla Coil. I put the two
doorknobs in series for a value of 1000PF at 80KVDC (well at least the caps
should never fry from over voltage!). I fired it up and with a few
adjustments to the spark gap got consistent firing with about a 1/8 inch
gap. Being totally out of tune I did not expect much but was pleasantly
surprised when I could draw 1/2 inch sparks from the top load. No breakout
but it did light a florescent tube a few feet away.

This seems entirely consistent with Ed's results from several days ago. It
also suggests my original problem was in fact way too much capacitance for
such a low powered coil. At .01uf I was effectively showing the spark coil
a short. In fact 1000pf is probably the maximum this one can go and a wider
spark gap could no doubt be had at 500pf.

Now to tuning and primary geometry: 

I am going to have to rebuild the primary since I had never planned on such
a small cap and have far too few turns to get it in tune. At present it is
a 45 degree conical primarily because I couldn't decide between a spiral
and a helix (it seemed a good compromise at the time and it does look cool :-).

Since I probably need all the coupling I can get, I am now leaning towards
a helix. What say you all, spiral or a helix?

The only downside that I can see to a Helix is that it takes far more turns
to tune with a helix. Using JavaTC I find I need 26 turns with a spiral and
58 turns with a helix. Does this seem correct and why?

Thanks again for all your help,

Dave

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