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From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Wednesday, June 25, 1997 3:31 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Building a new coil

Hi Rod,

> From:   Rodney Davies[SMTP:rgd872-at-anu.edu.au]
> Sent:   Wednesday, June 25, 1997 12:25 AM
> To:     Tesla List
> Subject:    Re: Building a new coil

> > > I'm designing a new small TC for my neice to build for her high-school
> > > science project.
> > 
> > Way to go :) I guess she won't have too many problems 
> > attracting/repelling the blokes in a few years.
> 
> :-) not like she's got the problem now... :-)
> 
> > > I've done a few rough calculations, plus using a few rules of thumb, I've
> > > come up with this design -
> > > 
> > > Secondary:
> > > ----------
> > > Sealed 4" diam PVC pipe, 22" long.
> > > 740 turns of 22 guage enamel coated copper wire closewound.
> > > Winding length of 20".
> > > (I take it that #22 wire is 0.67 millimetres thick?).
> > > 
> > > Estimated self resonant frequency (unloaded): 317kHz.
> > 
> 
> > I get about 570kHz unloaded.
> 
> Bugger, everyone's getting 500Khz+...  I used the formula -
> 
>         300,000
>     f = ----------------------------
>         T x w x Pi x (0.9144/36) x 4
> 
> Where T = 740 turns
>       w = 4"
> 
> I get 317Khz....???

I threw those old formulae away years ago. Best to use Wheeler for L 
and Medhurst for C.
 
> > > (Frequency should drop to a lower frequency with top toroid.
> > >  BTW, does anyone know how to do a rough calc of a secondary res.
> > >  freq. with a known capacitance of a toroid and height above
> > >  top secondary turn?)
> > > 
> > > Top Terminal: 12" x 3" toroid. (approx 12.95pF)
> > 
> > My (educated) guess on that toroid above that coil would be about 10pF
> > additional C which would make about 18.5pF total so I'd say it would 
> > resonate about 380 - 390kHz all up.
> 
> Hmmm, not too bad of a frequency either, probably get thin long hair-like
> streamers...and lots of them...

Actually, high frequencies aren't as bad as some suggest when it 
comes to attached streamers. The ones I get from the mini coils at 
around 1.3MHz look pretty much like the ones I've gotten on my 
largest coil. The air streamers are quite different though but at 
very low break rates. But that's at 1.3MHz.

Cheers,
Malcolm
<snip>