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Re: LITTLE TC PIX
Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>
Tesla list wrote:
> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Hi Ed:
> PLEASE keep us posted with your little coil progress. I'm just dying to
> start a bug zapper xfmr based TC to further the small end of the coiling
> spectrum, and yours seems to be on that same scale. Is that what your
> xfmr is? I'll probably be using a single blown static gap, have you
> tried adding forced air to your gap?
> BTW, is that a gray METAL box that the primary support is resting on?
> If so, I suspect it will be robbing a significant portion of the primary
> energy as it will appear as a shorted turn closely coupled to the
> Regards, Gary Lau
> MA, USA
1. The transformer is a 3 kV, 18ma jobbie I salvaged from an old vacuum
gauge controller. The only Zapper transformer I have (other than the
one in the back-yard Zapper) is one Terry gave me, and it is capable of
about half as much power. His measurements show 3.4 kV and 7.4 ma with
120 V input, and I measure 7.5 ma and 3.3 kV. I haven't tried it with
this coil yet. The other small transformer here is a 2600 V, 22 ma job.
2. The gap is a Victoreen SGCA-2500D sealed voltage protector once
available from All for a buck each; there was some discussion on them
here at the time. It's about 5/8" OD x 1-3/4" OD (going by memory, too
lazy to go down to the basement and measure it). The 2.5 kV breakdown
voltage is a bit low for this transformer, and I get a significant
increase in streamer length when I substitute a straight gap set to
"just fire" on the transformer voltage alone. There are two advantages
of the sealed gap. First, it is small and required no construction.
Second, it is SILENT! I have plans to replace it with an adjustable
four cylinder gap some time soon, when I have the ambition. There is
room for it in the box I am using. Should give more streamer length
and, unfortunately, more noise. I think that, at this rather small
power level (about 65 watts line input), the cylinder gap will work just
fine unblown. It will be made from four 1/2" pipe couplers mounted
vertically on 1/16" glass epoxy board, to allow some convection
cooling. I think that at the very small spacing of the individual gaps
it will quench OK, not get too hot (melt the board or whatever), and be
fairly quiet. We'll see.
3. The box is indeed metal, but doesn't seem to make any difference at
all in the performance. Get same tuning and output when I remove the
transformer/gap/capacitor assembly from the box and run it bare on the
bench. The box can be approximated by a single low-resistance shorted
turn of about 7-1/2" OD and I think the coupling to the 3-1/2" OD
primary is pretty small; will calculate that and report later.
I'll be interested in following your small TC projects. Keep us
posted. Question for you: Do such small coils necessarily give better
results than larger ones when operated at such low powers? I suspect
the major difference will be in the differences in breakdown voltage of
the upper terminal, which can always be controlled with some form of
"breakout bump, point, etc.", and that the streamer length is dependent
almost entirely on the power input, as Dunc has reported.