1/4 lamda and intial sec design parameters

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


Using a large top load capacitance, ie 2-4 x the dia. of the sec coil, helps
force the best resonant point near the 1/4 lamda point.  Also, the large top
load, sphere or toroid, reduces considerably the values of the minor
resonances and allows the experimenter to get maximum gain and performance
at a single frequency.

German experimenters first published these ideas in the 1930's--- most of
the publications are written in German but one can clearly see the large
toroids they used on resonance transformers.  Tesla of course using some
toroids to keep his ceiling exit point (his high antenna) from setting his
wooden pole building on fire, but the German group was the first to see it's
value to control the electrostatic field of the sec. inductor and reduce
unwanted resonances.


Our TC design procedure is like this:

(1) Keep in mind the larger the radius (dia.) of the sec. coil the better
the gain (voltage multiplication) is.  For this reason I always use a
reasonably large dia.  With a NST I would use 6-8 inches.  With pole xmfr
powered coils I always use 18-36 inch diameters and 40 to 72 inch diameters
on really large systems.

(2) I use a 4.5:1 height/dia ratio for almost all coils.  I always suspected
pi or 0.9 h as being the best but it causes too many sec to primary strikes.

(2) With a given dia. this gives the correct lineal winding length.

(3) Next, knowing the correct winding length, divide this length by 1,400
turns.  This will give you the OD size of the wire to use.  I always use 200
degree C wire as it has excellent insulation in coils that will be "pushed"
a bit.

(4) 1,400 to 1,500 turns on the sec gives excellent performance from almost
all coil designs.  Magnifiers can use 1,600 to 1,800 turns for good
performance.  Use 200 degree C wire on most designs up to 18 inch dia and
then switch to mil spec D 3 kV PVC at 18 inch dia and above.

(5) Allow enough distance from the coilform end to the first turn.  1-3
inches works well for most NST coils and 3-4 inches are required for 10-14
inch dia. coilforms.  At 18 inches dia we use 7 inches and 9 inches for 24
inch dia. coilforms.  This sets the proper coeff. of coupling for optimum
performance without the need to raise and lower the sec.

(6) Use a top load cap of 2.5 to 4 times the sec. coilform dia.

(7) Use John Couture's TC program, or Bart Anderson's JAVA TC, or R. Scott
Copperfield's WinTesla program to finish off the design.  These programs
will do an excellent job of providing you with pri turns, pri cap size, xmfr
size, and other data necessary to match your pri to the sec system.

(8) I always start by designing my sec coil (as listed above) and then match
everything on the pri side to fit.

(9) Use a sig. gen and oscope for initial tuning.  Always use a scrap wire
pri for initial tuning.  Save the nice looking copper tubing (expensive
part) until you get everything optimized --- then replace the scrap wire
pri. and always add 2-3 extra turns when using the copper tubing in case you
miss the resonant point.


No racing sparks --- works every time!

Happy coiling!

  Dr. Resonance

 >
 >
 >  >  >   > > There is only one fundamental resonance.
 >      I may be lifting this too farout of context, but....
 >
 >      Essentially any resonant system, especially _system_
 >      Will have more than one resonance.
 >       (Yes, only one will be The Fundamental,
 >        the others are quite real...)
 >
 >      The trivial case of a quarter wave straight wire will have
 >      f, 2f, 3f, etc
 >
 >      Wind the wire up and the stray capacitance and others effects
 >      will change the fundamental, the harmincs and add a few nearby
 >      ones.
 >
 >      Add a capacitance top hat and another set is _added_.
 >
 >      Set a resonant primary tank nearby and the complications,
 >      the real world, real realities get numerous...
 >
 >      (OK: I had unfair advantage of a tracking generator/spectrum
 >       analyzer to observe these, they can be seen with any
 >       equipment, and enough patience....)
 >
 >      Some/one will be stronger/strongest, the others exist,
 >      and affect things.
 >
 >      best
 >       dwp
 >
 >
 >