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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