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Re: My 8" secondary



Hi Ed, All,

Thanks for the kind words from a professional coiler. If it works as good as
it looks (pictures will be available on my website some time end of the month)
I will be happy. A 8"x 50" toroid would be really HUGE (whew !!). I donīt know
if I can find AL dryer duct hose with a 21 cm diameter. I would hate to use
plastic stuff and wrap it with aluminum (doesnīt look very pretty) foil or
tape.

I was planning on powering the coil with 6 NSTīs (voltage matched, in
parallel) Total current would be around 600mA, but due to german law, only at
a relatively low voltage (7.5kV; 10.6kV PtP). If this doesnīt work, I will
rewind an old 8kVA welder transformer (Iīve already taken it apart, started
making new wire formers, etc) for high voltage (Input: 380V (across two
phases: keeps the input current low) // Output:12-15kV-at-300-500mA). 

For starters I planned on using a multiple static gap made from 6-7 pieces
(5-6 gaps) of 35mm (1.3") copper pipe each about 4-5" long. Maybe two of these
in parallel to keep the heating effects down to a minimum. I also plan on
building a SRSG sometime in the future.

My capacitors will be homemade rolled PE type. I asked Siemens over here what
a 0.1uF 30kV ceramic cap would cost and they told me depending on end design
somewhere around $2500-$3000. (Yes thats $$īs, not DMīs. Theyīre crazy !!!
Esp. if the cap goes poof after a few seconds of operation). I was thinking of
using somewhere between 50-100nF for this coil. A mains reso cap would be too
big (somewhere around 254 nF) and as I have 4.5kVA input power at my disposal,
I donīt think it would be necessary. With 50-100nF I should be able to up the
break rate to 400-500 BPS (later with the RSG) and still be able to fully
charge it with my NST psu. Oil used will be either Shell Diala-X or castor
oil. Castor has a much higher K value (4.5), but Iīm not sure how long castor
oil will "last" as it oxidizes when in comes in contact with air. 

Malcom told me he had designed a 100nF cap for his 9.9" coil: 
Malcom wrote:
"Details of construction are online on Jim Fosse's homepage. There are 
(from memory) 12 plates, each 1 metre long. Dielectric between the 
plates consists of 2 layers of 0.25mm polyethylene. A 12 metre long 
roll of cooking foil just does the job."

I would be interested in having a look at Jimīs site. Anyone know his web URL?
Jim: Are you out there? 

The only thing which "bothers" me is the very small (0.5mm=19.68 mils)
dielectric distance. I was thinking of somewhere around 48-55 mils for my
7.5kV input to play it safe. However, I donīt know  what voltage Malcom was
using to power his coil.

BTW: Does anyone have a formula that allows you to calculate the physical size
(diameter) of a rolled cap (given total thickness of everything before
rolling)?

What I am not sure of yet is the primary coil design. A helical coil will give
me too much coupling, plus it would invite flashover (unless I build a monster
primary size-wise). However, I donīt know if I should go for a conical primary
(low angle, say 15°) or a flat primary. I donīt know if the flat primary would
give me enough coupling. A conical coil would be a little harder to wind (as
it is supposed to perfrom well AND look good)

My RF ground consists of 4 pieces of 40mm galvanized (1/8+" thick) T-iron
(each about 4+ ft long). I smacked these about 4 ft apart into the soil (all
except the last one, which is 2" out of the soil) about 8" under the sod level
(with ease) and interconnected them with 10mm^2 wire. From the RF ground to
the coil I run 16mm^2 flexible welding cable. I think this ground should be
"ground"-able enough.

Coiler greets from germany,
Reinhard 
 
<< 
  BTW: I just finished my 8" secondary:
  
  Coiler greets from Germany,
  Reinhard
   >>
 
 Reinhard,
 
 Sounds like a great secondary.  This coil will take a monster toroid if you
 have a large enough power supply to drive it.  I would think a 6 to 8" radius
 x  50" diameter toroid would not be too large.  What kind of supply do you
 have?  Rotary gap?
 
 Ed Sonderman