flat vs angled primary

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