Re: The 1500t secondary myth (long)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Ed,

Very interesting.  I fired up my 15KV 60ma 8 inch coil with a 120pps SRSG  a
couple of weeks ago at the Denver TC meeting and got 67 inch arcs (one
witnessed a 74 inch arc that I missed seeing).  Tonight I calculated the
secondary (with 6x24 toroid) impedance to be 47Kohms (so maybe I should try
a slightly larger toroid).

I had this thought experiment tonight that might explain the 36Kohm sweet
spot.  If one lets the secondary be a thevenin voltage source with a "fixed"
source voltage,  one would expect that maximum power transfered to the
streamers would occur with zero source impedance (think of varying the
source impedance instead of varying the load impedance).  However, as one
lowers the source impedance of the secondary, either Ls gets smaller or Cs
gets larger.

If Cs gets larger and Cp stays the same, both Ls/Lp and Cp/Cs would get
smaller.  The "fixed" source voltage is no longer fixed and would also get
smaller.  Eventually we lose more due to loss of source voltage than gain
due to lower source impedance.  Conversely, if we increase the impedance to
try to increase the source voltage, at some point we lose more due to source
impedance than we gain in increased source voltage.

If Ls gets smaller and Cp and Cs stay the same, (Im neglecting the portion
of Cs that is in the coil for this purpose) then Lp must get smaller to stay
in tune.  Currents in the primary go up and losses increase.  At some point
we lose more in losses than we gain due to source impedance and so on.

Maybe the optimum point can be determined analytically.

Gerry R.


> Original poster: Ed Phillips <evp@xxxxxxxxxxx>
>
> "The new theory that I have been working on (with a lot of input from
> Terry,
> Malcolm Watts, and others) suggests that the sweet spot is not any
> particular number of turns, or even any particular inductance. Rather,
> it's
> when the resonator has a characteristic impedance (Zo) of around 36,000
> ohms. Zo is a function of both secondary inductance and secondary/toroid
> capacitance:"
>
> It sure sounds reasonable to me that there should be an optimum value
> of Zo.  I haven't been following things enough to see where the 36k came
> from but assume it goes with a more or less constant streamer impedence
> (????) and some desired value of loaded Q.
>
> It's fortunate for TC nuts that there is a such a wide latitude in
> parameters which will yield satisfying results!
>
> Ed
>
>