flat vs angled primary

From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Saturday, April 18, 1998 11:28 PM
To:  Tesla List
Subject:  Re: flat vs angled primary

to: Tristian

Overcoupling was probably the culprit.  Check your coeff. of coupling and
keep in the 0.18 to 0.22 range for most coils.  Most coils thus require a
flat spiral to prevent overcoupling effects which produce standing waves
that can surge back into the primary and create your gap firing problem.


> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Subject: flat vs angled primary
> Date: Saturday, April 18, 1998 6:10 AM
> ----------
> From:  Mad Coiler [SMTP:tesla_coiler-at-hotmail-dot-com]
> Sent:  Friday, April 17, 1998 10:53 AM
> To:  tesla-at-pupman-dot-com
> Subject:  flat vs angled primary
> Tesla List,
>   I have recently built a new flat spiral primary coil for my small 3" 
> diameter TC. Previously I had a vertical helical coil (wound strait up). 
> The old primary was 5 turns of 1/4" copper tubing, and for my previous 
> setup was tapped at about 4.5 turns and the coil produced about 15"-21" 
> sparks. This setup is seen in the pictures that is on Chip's webpage. 
> The main problem was that with only 5 turns I couldnt put a bigger 
> topload on the coil. Also, there was always a problem with primary to 
> secondary arcing, even with the 6" PVC sheilding. Safety gaps accros the 
> NST seemed to be firing too often for my taste.
>   I built a new primary, flat spiral, #12 solid wire, about 12 turns 
> spaced at about 1/4" between turns. With the same setup and the new 
> primary coil (after tunning) the coil produced just a couple inches less 
> thean old coil. One thing I noticed right away is no safety gap 
> activity. I brought the gaps about 1/8" closer and still no firing of 
> the safety gap. My next test was to take off the 10" sphere I had and 
> put on a larger toroid. I took the top half of the sphere off so the 
> toroid could sit on the bottom half that was already connected. With a 
> 6" x 22" aluminum ducting toroid, (after retuning) the output increased 
> to 29" sparks. There was still no safety gap firing. I guess I should 
> try and bring the gaps a little closer. I think this coil is about at 
> max because the secondary is only 15" tall and the 29" sparks are 
> looking as though they want to come out of the top and bend around 
> almost getting back to the primary.
>   I was wondering why the helical primary caused much more safety gap 
> firing. I thought of two possibilities. One was just because there was 
> slight corona discharge between the pri and sec coils that could be 
> placing an unwanted potential in the primary circuits. The other was 
> that the helical coil was more tightly coupled to the secondary and that 
> the secondary could then be inducing a higher current into the primary 
> circuits by mutual coupling?  
> Comments are appreciated,
> Tristan Stewart