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Re: V-27 tube coil: latest results
In a message dated 99-12-18 01:35:09 EST, you write:
<< Original Poster: David Trimmell <davidt-at-pond-dot-net>
> Hello,
> This is a interesting thing about CW (at least tube based, in my
> experience), to get really high voltage (long sparks!) you must have a
> sharp breakout point extending several inches from the coil, or coil and
> top C.
Hi David, all,
Duane Bylund did some antenna-type voltage measurements of the
output voltage of his solid state CW coil. He found that the voltage
goes higher to about 125kV when he uses a ball on top of
the resonator, then the voltage drops to about 65kV when the spark
emits. When he used a point instead of a ball, the spark reached
only 65kV, but the spark length was the same in either case. The
higher voltage with the ball in place is to be expected because of
the greater voltage hold-off of the larger ROC presented by the ball.
The ball was relatively small on Bylund's TC BTW. (The voltages I
mentioned might not be exact....I'm writing this from memory.)
>Now, I have obtained spark breakout from a "relatively" smooth
> toroid, but only with extremely nasty kickbacks to the tubes (some sparking
> between plates and filament/grid) or back to the transformer. I cannot see
> any reason to use a toroid in a CW (tube) coil except for a corona shield
> and/or to assist with tuning (I use it for both), only use a protruding
> breakout point.
When I use the toroid with the point on top, the spark looks a little
hotter to me (vs, no toroid) and it might have more of a tendency to
aim the sparks more in an upwards direction rather than outwards.
The toroid may actually behave as an electrostatic focusing element,
forcing the sparks upward. The combo of the hotness, and the
upwards-aiming might help to make the spark longer. But it is also
possible that CW coils also benefit from a little top C in the same
way that spark gap TC's do. The extra C may help by acting as a
current source for the spark growth. This is speculation on my part.
In any case, I gain about 1" in spark length when using the toroid
beneath the point. I did a careful comparison with and without the
toroid, and retuned using a variable tuning cap, etc, and I got longer
sparks with the toroid, at least when using my small 3" by 12"
secondary. (Confounding factors are that the frequency is lower
with the toroid in place, and the tank Q changes some, due
to the way I retuned by using more tank C. So it is possible that the
toroid is bringing those parameters closer to an optimal operating
point, and benefiting the spark length in that way, so that's another
possibility.)
I kind of like the way the coil looks with the toroid on top also. And
when the sparks reach about 29" or so, a toroid or corona shield is
needed to prevent the sparks from breaking out from the top winding.
Undoubtedly, more work needs to be done to analyze why various
types of sparks look the way they do.
Regards,
John Freau
>Have such a different response with CW -vs-
>Disruptive coils (spark gap...)? Any body ever try to determine the voltage
>of CW coils? I doubt a spark length comparison with disruptive coils would
> be very close...
>Regards,
> David Trimmell >>