Jumping in with both feet?

From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Friday, January 30, 1998 8:51 AM
To:  Tesla List
Subject:  Re: Jumping in with both feet?

Tesla List wrote:
> ----------
> From:  SBJohnston-at-aol-dot-com [SMTP:SBJohnston-at-aol-dot-com]
> Sent:  Wednesday, January 28, 1998 12:59 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Re:  Jumping in with both feet?


> >You may want to make a simple small toroid from 3-4"
> >aluminum dryer duct - check the archives for details.
> Thanks for the tip -- I downloaded some material on toroidal terminals and
> I'll check it out tonight.  Any suggestions on the diameter of a dryer-duct
> torroid for this rig?

Try 3" or 4" diameter material to start with and make the outer diameter
a bit larger than your coil diameter. For example, if you make a 4" x
20" top terminal you're going to add around 15 - 16 pF of topload
capacitance. This is probably about the most you can drive and still be
resonant with the primary, since the new topload will drop your
secondary's frequency down to around the 120 kHz level that the primary
appears to be tuned to. This should prevent premature breakout from the
top of the secondary. If your system won't break out with the new
toroid, you can make a little "bump" on the outer surface of your toroid
from a piece of taped-on aluminum foil to promote breakout. With the new
topload, you'll need to use all of the primary winding.

> I'll have to try and see if I can find any markings on these strange-looking,
> finned capacitors.  Perhaps they could not handle 15 kV, so he used half the
> output winding.  Or it could be that he wanted to ground the case of the
> transformer for some reason -- in this unbalanced circuit that would make it
> impossible to use the other half of the winding.
> Oh - how about this... If I cut one cap loose, that would drop the total C to
> 0.015 uF - closer to what you spec for a proper transformer load.  This in
> turn would change the res freq of the primary to about 140 Hz (with the full
> 11 turn primary coil).  Sounds about perfect!  Hmmm..?
> Thanks for all the excellent information, Bert.
> Steve Johnston
> sbjohnston-at-aol-dot-com

Sounds like it's be worth a try - go for it! You'll need to add the cap
back in if you add the toroid though. Good luck, and welcome to the
world of coiling!! 

-- Bert --