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Re: [TCML] Newbie Grounding Question
Hi Terry,
(I've rambled here a little, sorry about that - I'm currently on holiday!),
Field control I work on by changing toroid size (ROC, diameter, and
height). I like to build toroids which are wider than the primary in
their outer edge size. I typically have found that a toroid outer
diameter works well when the center to center outer diameter is equal or
greater than the primary outer turn. Changing the radius of curvature
(the minor diameter) will change the breakout voltage. The minor and
major diameters should be kept within reason. The minor diameter should
be larger than the secondary diameter.
Toroid elevation above the ground plane is important. As far as moving
the toroid above the secondary, this is good to do but not so far above
the secondary that corona develops on the top turns. Another field
control situation is using a corona ring just above the secondary
allowing the main toroid to be adjusted even higher above the secondary.
My main adjustment is the toroid above the ground plane. Not only the
toroid, but the entire coil itself. You don't want the primary next to
floor.
It's a trial and error adjustment and if you only have 1 toroid, you
have to the best with what you have. Toroids are difficult to build.
When I stick to some of the above conventions, I get good field control
with just some elevation adjustments. Tuning really should be a little
high on inductance about 5% above the resonant value. When sparks break
out, the sparks themselves add a slight loading which can result in the
need for a little added primary inductance to stay in resonance with the
resonator as it changes with the spark breakout. Coils really do run
smoother, less racing sparks, etc.. with added primary inductance.
A nice smooth toroid surface is very helpful as well to keep the
breakout voltage as constant as possible. Sparks will want to rise
upward if possible by the thermal rise of the spark channel. But if the
ground plane is near, it will head down. The sparks are no different
electrically than any other conductor. They "will" seek out the lowest
impedance - period. As sparks are given more power, they will issue
further out from the top terminal. As they do that, the ground planes
impedance becomes more and more apparent, so eventually, sparks will
seek the floor. Hopefully, it is far enough away from the primary. If
the coil is low to floor, it will seek out the primary more often at
even lower power, and the primary can be seen as a nice low impedance
target.
I keep my coils primary usually 30" or higher above the floor. Field
control is opinionated and have my opinions like everyone. It's not an
area that has been discussed much on the list. From my personal
experience, elevation above ground is one of the major factors.
Something I have noticed. If sparks have just enough power to hit the
primary and nothing else, there will be more primary strike occurrences.
In this case, toroid diameter can be very helpful to keep the sparks at
bay. Also, larger ROC helps in this situation. Sparks will always start
about 20 degrees above the horizontal center of the toroid. The larger
ROC helps in this regard. If the ROC is large and smooth, a single
streamer at any one time is the result. This is kind of cool. I've had
single streamers move almost halfway around the toroid before another
streamer issued elsewhere. Kind of a cool thing to watch. That
particular case took a large 9" x 30" toroid on a 4.5" diameter
secondary: 3 coil TC (not a true maggy as all 3 coils were magnetically
coupled). But amazing to break out of that size top load on such a small
coil.
Take care,
Bart
Terry Oxandale wrote:
<But first I would try to get some field control on the sparks
themselves.
Take care,
Bart>
Could you expand on this control and how it is affected?
Un-Terry
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