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magnifier vs. classic tc (magnifier modeling)


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From:  FutureT [SMTP:FutureT-at-aol-dot-com]
Sent:  Saturday, March 21, 1998 10:43 PM
To:  tesla-at-pupman-dot-com
Subject:  Re: magnifier vs. classic tc (magnifier modeling)

Antonio, Malcolm, Bert, all,

I've added more C2 as suggested by Antonio, by installing one of
Lou Balint's variable tune caps across the secondary coil.  This gives 
me a cap range of 38pF to 164pF (and maybe more).

I used the 1.5mH secondary with the 11.2mH extra coil to try to keep
the voltage across the cap limited to reasonable levels.  I left the pri
tap at the same point (turn #19) that I used before without the tune 
cap.  A 1 1/2" by 5" toroid was used with a sharp point on top.  The
strongest sparks occured using the full 164 pF.  (The cap can be
set up to give more than 164pF, but it's voltage capability then drops
to half...so it may arc internally...I didn't try it).

I can see strong beating effects in the after-quench ringdown 
waveform on the scope.  This beating changes drastically as I 
adjust the variable tune cap. The beat period can be made long or short,
by adjustment of the tune cap.  The beats before the quench are 7uS
long when the variable cap is tuned for best spark *without* the sharp
point.  This suggests an effective coupling of k = .28 or so, which 
represents a significant tightening from the earlier *no cap* tests, 
which showed a k = .18 effective coupling (but...see below).  This
tune point also corresponds to the formation of *well formed* beats.
The tune cap has to be readjusted (to 38pF [minimum cap]) for best
spark when the point is added to the top of the toroid.  When this
point is added, and the cap tuned for best spark, the beats blur
together. Maybe when the point is not in place, delayed streamer
breakout permits stronger beating to occur between the secondary
and the extra coil before breakout.

In one case, the RF formed what looked like a beat that was
34uS long which would imply an effective k = .06.  Calc. is about 
k = .14.  In still another test, the beat period seemed to be 24uS, 
but in both cases, there were visible beats within the main beats. 
So the effective k depends on which beats you look at.  When the
point is installed on the toroid, then the RF rings down lower and
lower as each beat occurs.  But when the point is not installed, the
RF rings up over a number of beats, then down over a number of
beats.  This is what gives the appearance of one long modulated
beat (and there are a number of these large ones too, these long
beats ring only down from beat to beat, never up).

Regarding the effective k = .28 above however (no point on toroid),
it would seem to me that the energy might not be fully transfered
during these beats, these may be false *pseudo-beats*.  I have to
look at this again. 

I also tried tuning the primary at turn # 20, results were a little
different, but I have to recheck this.  The only other tune point I
tried was around turn # 24, but no sparks were obtained.  The
variable tune cap doesn't seem to affect the overall frequency very
much.  But tuning of the variable cap was very critical in all these
tests.  I didn't recheck to verify that Fo was somewhere around
500kHz.

Some variable cap adjustments resulted in a modulated appearance
in the sense that two beats would be strong, then two were weak,
then two were of intermediate height, then two were weaker yet, etc.

I also ran the coil without the variable tune cap, and I can see that
the beats *are* occuring after the quench even with the small self C
of the secondary (or it certainly looked that way).  The spark output
is a little weaker without the variable cap, but tuning is probably not
as precise.  Without the variable cap, the beats were about 10uS.

I may try using the 5.75mH secondary coil, but oil breakdown may
occur in the variable cap.

More work is needed.

John Freau