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Re: NE555 driven coil WAS:Re: SCR driver coil...



Hi Paolo,
         Here are some details from memory (notes at home):

> Original Poster: Paolo <pagaiard-at-geocities-dot-com> 
> 
> Hi Malcolm,
> thanks for this fine information:-)
> 
> > 
> > Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
> 
> >     A couple of years ago I scored 6" p-p sparks in a mini-twin
> > disruptive coil running a 30W input power. I'd recommend this mode of
> > operation any day.
> It will be ok if can keep the resonance freq around 100-300KHz,
> what was the resonance frequency and physical dimensions of your
> mini-twin coil arrangement?

Resonators: 7"H x 2"D  (I think I think - I know the 7" is right) 
            0.3mm dia copper wire closewound.
            
Primary cap: 2 x Sangamo micas in parallel (3.9nF each).
Max voltage 6kV peak  (safety gap set to 7) 
Gap single static 1/4" tungsten carbide tipped brass, fully 
adjustable while running.

I built a flyback SMPS to power the system safely from a mains source.
Max cont. output was about 30W.

Primary 4.5" dia  about 4 turns closewound 1.5mm copper wire.

In twin configuration, I used the bottom of resonator 2 as the earth 
for the driven resonator.  Fr ranged from about 1.1MHz no load to
800kHz with a couple of small stacked toroids topped by a 3" ball.
Pretty broad tuning which made it great for experimental stuff. I 
think I scored best length with a 2" dia ball on top of each coil
and the gap set to around 4.5kV. Power input was constant so BPS went 
up as the gap was closed. Most spectacular display with single 
earthed resonator was obtained with a 3" ball on top. There was a 
ball of wispy streamers extending down to the spark gap cover. 

BTW, I've since sold this system and to my knowledge, the Sangamos 
are handling this abuse just fine. The other day I chased up a US 
firm which sells them to the RF market and was horrified to learn 
they cost somewhere around $80 - $100 each!! No wonder - excellent 
coiling caps they are! I was given a bundle by someone who obtained 
them surplus from a broadcasting outfit and had them lying around in 
a basement for yonks.

Malcolm