# Re: Extra coil and corona on connection wire

```Don Allen wrote:

> It was suggested that I should be using a larger diameter secondary
> for the driver coil, possibly an 8" coil form. Any ideas how many turns
> of wire, and how much winding area on the driver coilform I should
> strive towards? My current specs are a 15/60, 6" secondary coil
> and a .01 mfd cap using the RQ static gap system.
>
> I wasn't originally aiming at a magnifier, but since it didn't take long
> to wind a second coil I might as well investigate this further. :)
>
> In some of Tesla's schematics listed in the Colo. Springs notes..he
> shows condensers connected at some possible points along the
> secondary. I'm curious what would happen if I connected a 50kv .01
> mfd cap at the top of the free terminal on my working coil and
> connected the other end to either a second coil, or a larger topload.
> What would most likely be the outcome? I'd rather understand the
> theory first before sacrificing a good cap. <g>

You can use the expressions (from my site):

1) w*w*L1*C1 = (2*m*m*k*k+(m*m-l*l)*(l*l-k*k))/(2*k*k*l*l*m*m)
2) w*w*L2*C2 = (l*l)/(k*k*m*m)
3) w*w*L3*C3 = 1/(l*l)
4) L2/L3     = ((l*l-m*m)*(k*k-l*l))/(2*k*k*m*m)
5) k12*k12   = ((k*k-l*l)*(l*l-m*m))/(k*k*(l*l+m*m)-l*l*(l*l-m*m))

Starting from the third coil resonance frequency, that would be
1/(2*pi*sqrt(L3*C3)). This will give you L3*C3, and given l, you
have w from (3). You have also L3, so you can compute L2 from (4).
C2 is obtained from (2), and L1 from (1) and your primary
capacitor.
Choose k, l, and m as (1,2,3), (2,3,4), (4,5,6), etc. (k integer,
l=k+odd integer, m=l+odd integer) and experiment to see what
results in better values (probably 123, 234, 345).
C2 is the capacitor to add in parallel with the secondary coil,
discounting its self-capacitance and other parasitics, as
capacitance to the primary coil. Probably much less than 0.01 uF.
It is proportional to C3, and of the same magnitude order (pF).
A simple top terminal in the secondary coil may be enough if the
terminal of the third coil is not too large.
Once chosen the values, the normal formulas for inductances
and capacitances can be used. The coupling k12 can be estimated
and then adjusted for best results.

I really would like to see experiments with these relations.
For given primary capacitor and top terminal, a magnifier is
theoretically superior to a normal two-coils system, because
it leaves less energy in the coil capacitance, if the self-
capacitance of the third coil is made smaller than the self-
capacitance of the secondary coil in the equivalent two-coils
system. This is also true, although for a small margin, if the
secondary coil of a conventional system is used as third
coil in a magnifier, because the third coil can be mounted
in a high insulating pedestal, far from the primary and
from the ground, what decreases its self-capacitance somewhat.

Antonio Carlos M. de Queiroz

```