> Subject:      About to begin anew...

DK> I am about to begin begin my 7th Tesla-coil...    
DK> ... here is what I have to work with:

 > 2) 15 kV 60 mA neon transformers for 15 kV -at- 120 mA input

No problem with that.

 > 1) 0.02 microF 120 kV military surplus capacitor

Is this a pulse discharge rated cap with plastic film dielectric? 

 > 1) roll of 1/4 inch (.635 cm.) copper tubing for the primary

I would be moving up to a larger radiating surface primary
conductor for power levels over 1.5 kVA; 3/8" od copper pipe
would be my minimum requirement and I would look real hard at a
primary design using 1/2 od pipe. High tank circuit Q depends on
a high Q pulse discharging capacitor(s), large surface area
primary conductor wound into a high inductance coil, and a good
spark gap. I start with the capacitor and coil, you can always
change out or modify a gap.

 > 8) 18 inch x 1/8 inch (46 cm. x 3 mm) Aluminum plates for a    
 > series quenched gap 

Could you be more specific on this? Over 1.5 kVA  and I look for
some form of active quenching, and I never run even a small gap
without a muffin fan, or something, to aid in removing hot ions
and cooling the electrodes.

 > 1) roll of 24-gauge magnet-wire, polyurethane and polyamide    
 > coated 

Too small. I don't recco 24 gauge wire unless you are building a
tiny coil, you are performing an experiment, or have requirements
for huge amounts of inductance per a small unit volume (like in a
detection or "pickup" coil). 23 gauge wire is an improvement; but
I like #22 gauge or larger.

 > 1) PVC pipe, 10 inches (25.4 cm) in diameter, and 43 inches    
 > (109 cm) long 

Whoa! My largest secondary coil is 10.5 inches in diameter and 32
inches long. I run up to 10 kVA into the tank circuit and my
secondary discharges routinely hit 11 feet (132 inch strikes).
How about looking at an 8 inch diameter coil form? If you decide
to go with a 10" diameter secondary coil, you need to cut about
10 inches off of your aspect ratio. You did not mention anything 
about the number of turns, or the actual winding length.

 > 1) 12 inch (30.5 cm) non-magnetic, stainless-steel discharge   
 > electrode (This is shaped like a toroid... about 4 inches (10
 > cm.) thick. 

Too small for the eight inch diameter secondary, way too small
for a ten inch coil form, and not enough isotropic capacity for
this power level. I would recco a 20 x 4 toroid for starters.

DK> I have always spaced the wire turns in all of the larger      
DK> coils, but now I read that this may not be necessary. 

Not only is this not necessary, but space winding really reduces
the potency and potential of a coil. The origin of space winding
comes from two places: 

1) Classic coil construction materials: wood coil forms, cotton   
   or silk covered wire, and primitive rubber insulations (high   
   in soot and other particulates), were common until well after  
   WWII. If you are winding coils with any of these materials     
   then you will have to space wind because the coil will not     
   withstand high VSWRs in a small volume without electrical      
   breakdowns and excessive corona losses. Making a coil very     
   large in diameter and spacing the turns distributes the charge 
   densities. This in turn reduces corona losses and reduces the  
   incidents of breakdown. Tesla had to do this in Colorado       
   Springs, given his materials and power levels, we don't. 

2) Tesla, in his COLORADO SPRINGS NOTES, wrote about the problem  
   that he had with excessive distributed capacity in his second- 
   ary. This is a problem with very large diameter coils, which   
   Tesla built because of statement #1 above. He increased the    
   spacing between the turns to reduce this distributed capacity, 
   but took a substantial reduction in inductance (and the        
   coupling coefficient with his primary) which reduced the       
   simple transformer action of the primary/secondary coils. He   
   made up for the reduced transformation by increasing the       
   voltage from the supply transformer. He ran very large input
   voltages in Colorado Springs (20-60 kV) for this reason.       
   Tesla postulated extensively, and unsuccessfully, on ways to   
   eliminate 100% of the internal capacitance without reducing    
   the inductance. Eventually he simply learned to live with some 
   distributed capacity in his large coils. 

I submit that by using modern high Q construction materials and
techniques, some of the basic reasons for making large diameter
space wound coils become less valid. High VSWRs and charge den-
sities can be developed in much smaller spaces, without excessive
losses and breakdowns, by exploiting sealed plastic coil forms
and large toriod terminals. Distributed capacity becomes much
less of a factor when HUGE gains in efficiency can be obtained in
other areas: higher ratios of transformation are obtained by
increasing the secondary inductance; proper use of large iso-
tropic capacitances on the air terminal (big toriods) produce
greater base currents and larger VSWRs (with lower corona losses)
and allows much tighter coupling with a larger primary. This
really is a whole different ball game.

DK> I even built a kind of lathe that cuts threads in the forms
DK> in the desired spacing. Should I junk this machine? 

I hate to tell you. You know what I am going to say. 

DK> If any one of you had this same equipment and wanted to build
DK> a coil, what special considerations would you take?

Mull it over. Feel free to get back with any questions.

Richard Quick

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12