Re: Primary not quite stacking up

On Fri, 8 Oct 1999, Kent & Kim Schaffer wrote:

> Hello Everyone!
> Let me first start out by saying that we have three "will be there"'s
> (including both hosts) and two "trying to make it"'s for the MidOhio
> TeslaFest and we're still looking for more participants.  Also, for
> anyone that's ever hosted a Tesla Coil event, are there any tips,
> tricks, format suggestions, etc? 
> Now on to the main topic. 
> I've been working on primaries and some things just don't stack up.  I
> currently have: 
> 12" x 3" Secondary with a brass doorknob as toroid 7.25" id x .250"
> Copper tubing x .200" spacing x 9.6 turns flat primary 15Kv -at- .030 ma
> Xfmr .006 uf SW Cap tank 6 gap Static Gap
> This unit really dings!!  12"-14" discharges!! 
> Dave, and employee of mine, and I are starting on several new coils (for
> the 'Fest) and started plugging in numbers into WinTesla.  According to
> WinTesla, we have a primary with an inductance of .0328 mH.  Yet, while
> following the formulas found at www.pupman-dot-com for this coil we need a
> primary inductance somewhere in the area of .0198 mH.  What's the deal? 
> It almost seems as though this coil could stand more turns on the
> primary.  What is a good rule to follow when constructing a new coil? 
> Is it just total trial and error?  Do you just throw a bunch of copper
> into a spool on a flat surface and see what happens?  Did I calculate
> the required inductance wrong? 
> I see now that I calculated the primary frequency of .0198 while using
> the 1/4 wave frequency, but when using the resonant frequency in the
> same formula I now come up with .0037 mH.  When using this equation... 
> X(L)=X(C) 
> L=X(C)/2*pi*F
> L=inductance in microhenries for primary X(L)=Reactance of Cap
> F=Frequency in Mhz
>      ...to calculate the inductance needed for the primary coil, which
> "Frequency" should be used? 
> When building a coil, how do you settle on a good design and format for
> a primary?  Does this just come from experience? 
> Thanks,
> Kent