Re: Disappointing Results

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "David Kyle by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<dave-at-kyleusa-dot-com>
> 
> I fired up the desktop model T spark coil powered coil with very
disappointing
> results. It appears that the pulse caps I am using simply short out the spark
> coil as I get no spark across my spark gap even when it is nearly closed. So
> here is the question: is it my choice of capacitor or have I selected too
high
> a capacitance value for such a low power coil.

> The spark coil might be good for about one milliamp but I had not
expected .01
> would short it out. What value might be more appropriate? Would a
doorknob cap
> be a better solution for a very low power coil?
> 
> 
> 
> Dave

	Your capacitor sounds way, way too big.  It's been a long time since
I've used a Model T coil with a TC, but a few years back I played with
using an EXEL (SP?) coil and 12 V battery-powered driver.  That coil has
a lower output impedance than the Ford one, and got best results with an
0.0033 ceramic doorknob filter capacitor.  Plain gap spacing was around
0.05", and I could get 4" streamers with about 12 watts input.  At the
time I built that I did try a Ford coil, but it wouldn't drive that much
capacitance so put it back on the shelf.  Do intend to use it again and
try to duplicate the little TC I built in high school, circa 1941.

	Bottom line is that if I were you I'd start with something like 0.001
ufd and wind a higher-inductance primary; you'll probably find the
maximum gap spacing isn't much over 1/32", if that much.  You might be
able to use a bigger capacitor later, but you should get something out
with that value.

Good luck and report your progress,

Ed

Ed