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A Trap For The Unwary
---------- Forwarded message ----------
Date: Mon, 13 Oct 1997 11:08:25 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: tesla-at-pupman-dot-com
Subject: A Trap For The Unwary
Hi all,
I made a fool of myself when testing a coil this weekend. I
carefully measured the resonator frequency and then proceeded to
measure the primary and in the process reomove some of the tubing for
clearance reasons. Checked the coupled system on the scope and
everything looked Jake. Powered it up single shot, and imagine my
surprise when I got a measly 3" spark to a grounded rod. Went out and
watered the ground - same result. Then I removed the primary and
proceeed to re-arrange the lower half of it (stacked pancakes from
one piece of tubing). I imagined all sorts of contortions the coupled
fields might be going through despite having seen a nice high Q peak
on the scope. Turned out to be totally illogical and the original
should have been just fine.
I should have known better - that resonator with its topload
should have been resonating well below 200kHz rather than the 230 I
had noted. I even went back and checked to make sure I hadn't tuned
into one of the higher order resonances. I even had the ballpark
frequency recorded a few pages back in my notebook. I should have
b****y well checked before hacking into the primary. As a result, I
am going to braze the primary pipe back into one piece today before
rebuilding the original.
The problem? Despite the obvious pressure the contacting wire
going from the top of the secondary was exerting on the toroid, it
wasn't making contact due to oxidation. Of course it did with the
first few real volts going in thereby completely detuning the thing.
Having discovered that, I hastily stuck a larger cap on the now-
hacked up primary and scored about 11" single shot to a grounded rod.
So repetitive firing with the smaller capacitance was out and my
coiling was over for the day (no welding torch handy :( BTW, as I
noted in another post, that spark became close to 20" at 3BPS which
was the best the flyback test supply could do at its power level.
That was about 3/4 the resonator length. Spark was hot and bright
blue white.
:(
Malcolm