Re: 1st coils

Subject:  Re: 1st coils
  Date:   Sun, 15 Jun 1997 04:32:45 +0500
  From:   "Alfred A. Skrocki" <alfred.skrocki-at-cybernetworking-dot-com>
    To:   Tesla List <tesla-at-pupman-dot-com>

On Wed, 11 Jun 1997 23:51:07 -0400 Jim
<jwbuck-at-loclnet-dot-com> wrote;

> Hi everyone
> I just subscribed to this list a few days ago.  Actually I just got my
> first true TC built yesterday.  Anyway a few weeks ago I saw a picture
> of a TC on the net.  The primary looked just about like the insides of
> one of my ham radio antenna tuners.  I then looked around a little and
> found a schematic.  Well even the circuit looked similair to the tuner

A Tesla coil looks so similar to an antenna tuner because it is the 
grand dady of all tuned circuits!

> so I took a few hours and wound a secondary on 18" of 1 1/2" PVC pipe. 

Way to long! Tesla coils should typicaly have a length/diameter ratio 
of 2-1 to 4-1 .

> I put a metal strip on the bottom and soldered the wire so I could
> electrically connect the bottom of the secondary just by setting it in
> the tuner.  I connected a dummy load to the antenna terminal and
> proceded to tune the tuner with the TC secondary installed.  It worked
> best at 3800 khz but even then only gave off 2" sparks with the radio at
> full power (100W).

Small Tesla coils typicaly yield 12 inches of spark for every 300 
watts of input power so for a 100 watt unit don't expect better than 
4 inches on a GOOD design. I also doubt that that coil is resonating 
a 3.8 MHz you probably tuned to one of the coils upper harmonics 
which also would yield lower output.

> Since I really don't want to run the coil with the radio I built
> another coil in the last few weeks complete with primary & HV caps.
> I am driving this new coil with an old ignition coil connected to a
> 555 timer driving a SCR. Anyway when I ran the smaller coil with the
> HF rig at 3800 khz the sparks acted more like flames and I could touch
> them and not feel a bit of a shock (although I did burn my fingers a few
> times).  With the new coil,running at a much lower frequency, the sparks
> are way different. They are blue and shocked me when I touched one with
> a pair of pliers. They also make  noise where the first coil all I heard
> was the modulating signal I fed into the radio.

Your observations are typical of the comparison of a High frequency 
driven coil as copatred to a lower frequency. High frequency coils 
hiss and their discharge is flame like. The lowerer frequency coils
are noisey and theri sparks are longer for the same voltage and tend 
to rample around and branch. The reason the High frequency driven 
coil didn't hurt where as the lower frequency coil hurt is because of 
what is called the skin effect. At higher frequencies the current 
flows through a thinner and thinner depth of the conductor. So the 
current probably didn't penetrate your skin deep enough to contact 
the nerve endings. Also your nerves have areaction time and if a 
series of pulses hit the nerves quicker than the nerve can recycle 
then you can't feel it.

> Has anyone here built a high frequency driver for a TC?  I'm trying
> to figure out the best way to do it and I don't really want to have
> to build a high power,100% duty cycle radio transmitter.

A number of us are experienting with using R.F generators of 
various types to directly feed a Tesla coil and the idea of using a
radio transitter is not really a bad idea! The general reason to try 
directly feeding R.F. into a Tesla coil is to elimnate the noise and 
losses of the spark gap. Tube Tesla coils have been built but have 
thus far proven to be poor performers. Richard Hull has been 
experimenting with a Thyratron I think, on his latest magnifier and 
with very good results.


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                           Alfred A. Skrocki
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