Re: First light...Sort of

In a message dated 9/16/99 4:04:39 AM Pacific Daylight Time, tesla-at-pupman-dot-com 

> Original Poster: Aric_C_Rothman-at-email.whirlpool-dot-com 
>       I started up my complete coil for the first time, with disappointing 
>       results.  Vital specs (from memory) are:
>       Power Supply:      15 kV NST
>       Tank Cap:          0.01 uF styrene
>                           (0.04 uF 40mil dielectric x 4 in series)
>       Primary:           18 turns, 30 degree inverted cone
>                          1/4" soft copper tubing, 1/4" spacing
>       Secondary:         4.125" dia. x 51" long secondary
>       Top Load:          4" x 32" toroid
>       Spark Gap:         RQ style, 1/2" Cu tubing, 0.02" gaps, 10 gaps      
>       First off, I know the secondary is way too long.  It was the first 
>       part of the project I assembled and I didn't know what I was doing 
>       (not that I do now ;)
>       I tried several different tap locations on the primary, and managed 
>       get a few anemic purple sparks from the top load to the ceiling 
>       1 foot).
>       The PVC tubing around the RQ gap buckled, causing most of the gaps to 
>       short out, once this happened, no further sparks from the top load 
>       were produced.
>       I'm going to build up a new gap, probably consisting of a series of 
>       tube section glued to a sheet of phenolic.
>       As a first attempt to improve performance, should I slice out a 20" 
>       section of the secondary and use that?
>       Aric

I ran some quick calculations on your coil.  Assuming 51" winding length and 
5.5" I.D. on the primary, even using all 18 turns of the primary, I calculate 
that you need about 10% more capacitance to tune this coil.  I would cut 30" 
off of the seconday so the winding length provides a 4.5 : 1  or 5.0 : 1 
maximum ratio of winding length to diameter.

I would start with 5 or 6 series gaps with each gap set at .020 to .030".  I 
also recommend that you do some calculations to make sure what you plan to 
end up with will allow the primary and secondary to tune with somewhere 
around 70 to 80% of the full primary turns in use.  This makes sure the 
design is going to work and allows extra primary adjustment for adding more 
power, larger toroids, etc.

Since you are using a 30 degree primary, I would start with the lowest 
secondary winding set about 2.0" above the first turn on the primary.  Once 
you get everything running well you can lower the secondary in small 
increments to get the optimal coupling.

Ed Sonderman