Re: Information Unlimited BTC30 coil ??

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Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi  Jay,
(snipped out old stuff for bandwidth),

> How would I make a capacitor at 0.013uf   If I already had about 100 
> 7 by 5in aluminum flashing rectangles and I could buy a dielectric 
> from HomeDepo or someplace similar?
You mentioned improving this coil originally. Thus, I would recommend 
building an MMC. It will be the easiest to build and will perform and 
last longer than a homebrew cap. I'm unsure of your transformer size, 
but I seem to remember it was about 20 or 30mA at 9 or 12kV. The MMC 
capacitance will need to be determined on your transformer specs. But 
I think you will only require 1 string of MMC's, so it will be low 
cost. For example, if the transformer is a 9kV at 30mA, you could use 
the well tested 0.15uF Cornell Dublier caps. Hook 11 of these caps in 
series for a total capacitance of 0.0136uF.
> And how would the new capacitor effect the primary?
If the cap to the same capacitance of the current cap, it won't 
change the primary at all. However, if you change your primary, then 
you will need to adjust the cap accordingly. For example, if you wind 
a 10 turn primary as opposed to 5 turn primary, then the primary 
inductance will increase. Thus, the cap should decrease accordingly 
to satisfy the resonant frequency requirement (as determined by the 
secondary circuit). Fr = 1 / (2 x PI x SQRT(L x C)), so as L 
increases, C must descries to maintain the same frequency, and vice-versa.
> Would a conical primary work a little better than raising a spiral up a bit?
Nope. Raising the secondary will increase the proximity between the 
two coils causing the coupling and mutual inductance to decrease. 
With using and conical (inverse cone where the inside of the cone is 
lower than the outside and is the typical cone configuration), the 
overall mutual inductance and coupling will increase because the 
average proximity has increased. This will not help a high coupled 
secondary problem, but will increase the frequency of the problem behavior.
If the conical coil was an actual cone (inside of the primary coil is 
higher than the outside), then yes, the average proximity would 
decrease causing coupling and mutual inductance to decrease. However, 
this is particular configuration is no better than simply using an 
easy to wind flat coil and simply raise or lower the secondary as necessary.
Take care,
Bart