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Re: BIG resonance! - thoughts...



>Original Poster: Jon Rosenstiel <jonr-at-pacbell-dot-net> 
>
><big snip>
>
>Just after I had installed a brand new 6" secondary I got a couple of
>strikes to the primary while fooling with a small toroid and "poof", there
>went my 15kV 60mA NST. I tried to rebuilt the 15/60 but ruined one of the
>secondaries trying to remove it from the core. I couldn't find any more
>15/60's so I unpotted a couple of 15/30's, removed enough shunts to make
>them 15/48's and threw them in a oil bath. With the 15/48's in parallel,
>(96mA), I thought that my present .011 tank cap was too small and better
>performance could be had by having the "proper" sized cap. (for 15kV -at- 96mA
>that calculated out to .017uF).
>
>I spent quite a bit of time and effort constructing 4 extended foil rolled
>caps that had a total series value of .006uF  which when added to my
>original .011uF cap gave me .017uF. Imagine my suprise when my coil's output
>dropped with the .017uF combination! Couldn't understand why! Then I read
>your answer to Alex' questions and the light came on!
>
>I already had several .008uF-at-5kV caps lying around so I wired them in
>various series / parallel combinations so that I could test the resonant
>rise characteristics at various capacitances. It turns out that my 15/96
>transformer(s) still work best with a .011 tank cap.
>
>I fed my transformers 2Vac, got out 250Vac with no capacitor attached. I
>tested various capacitances and recorded the voltages, (made a nice graph in
>Excel).( I can send the graph if you want). All very, very interesting!
>
>I then hooked my Tesla tank caps to the transformers and got the following:
>
>     C                    Eout
>.011uF            1650Vac, (original cap)
>.017uF            606Vac, (original cap + new .006uF cap)
>
>No wonder my spark length dropped!  1650Vac is 6.6 times the 250Vac output
>that I got with no cap! I hope that the 6.6 times doesn't scale up linearly.
>If it does I think that my coil would have self destructed long ago.
>
>Now on to that larger toroid and a way to increase the coupling in that
>never-ending quest to achieve the longest possible spark!
>
>Regards,
>
>Jon

It sounds like knocking out NST shunts doesn't alter what their
mains-resonant capacitance wants to be.  Perhaps the only way to be sure
is to feed in a sine-wave function generator and sweep in the
neighborhood about 60 Hz.  I did this with my 15/60 NST and .01uF cap and
found them to be resonant at 60.5 Hz.  Not too far off the mark!

Gary Lau
Waltham, MA USA