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1st coils
From: Jim[SMTP:jwbuck-at-loclnet-dot-com]
Sent: Saturday, June 21, 1997 10:50 AM
To: Tesla List
Subject: Re: 1st coils
Thank you for the information & the time you take contributing to this
list.
> >
> > 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've tried smaller secondaries but the spark just gets smaller. The
primary tunes at far fewer taps. I've tried to remedy that by using
smaller caps and even though the primary re-tunes with more turns the
sparks just get smaller. I guess it could be a problem with my caps
since all my HV caps are rolled. I may try to build some multi plate
flat caps & try that.
>
> > 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.
Do you know if anyone has tried driving a TC with an arc transmitter
such as Valdmar Poulsen invented & briefly replaced the spark gap
transmitters of the time?
Thank again,
Jim