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New Primary tested
Original poster: "Jolyon Vater Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
I have tested the new secondary (440t on 3" dia 10 7/8 high) with 4.7nf
saltwater pop-bottle capacitor in primary tank.
with full primary (11 3/4 turns) this resulted in poor spark length -less than
Best results were obtained with very small number of primary turns e.g.. 2 1/2
to 3 1/2 turns, when a circa 2" spark to ungrounded object was obtained.
Calculations suggest the necessary primary inductance to resonate with the
4.7nF capacitor at a secondary self-resonant frequency (no toroid) of , say,
600kHz would be 14.97 uH -this figure looks somewhat dubious since the inner
radius of connected spiral is 1.5" and the outer radius is 5" (the inductance
of this was calculated to be only 1.8148148 uH )- although there are two 1.5
metre lengths of neon cable between the capacitor/ spark gap and the primary.
Might this not account for the missing inductance and if so, could I not in
theory shorten the leads and use more turns on the primary?
Also -since a toroid was attached to the uppermost secondary turn- wouldn t the
actual resonant frequency be lower than the self-resonant frequency and wouldn
t the primary inductance have to be even larger than 14.97 uH to get a match?
How is toroid capacitance estimated? Is there a reliable way of measuring
toroid capacitance -I am wary of "non-referenced" capacitance (isn t
capacitance always referenced to somewhere) and would like to know if/ how
distance from the base of the secondary affects the capacitance of the toroid.
The use of the pop-bottle capacitor in the circuit is precarious -the first one
blew and the second is seen to be engulfed with violet corona under subdued
lighting. I think 4 bottles in series-parallel would be less stressed and more
reliable -is this configuration likely to be OK?