Re: Certain s.s. phenomena

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>

Ken,

Maybe the coupling is not as tight using just one turn?  Did you
measure and adjust the couplings when using various numbers of
primary turns?  Maybe impedance matching becomes an issue?
Impedance will be very different before breakout than after, so I
guess some sort of compromise is at work.
>  
>  1.1  With the 3-turn configuration, spark appearance is essentially
>  identical while mains current, for the same spark duty-cycle, is reduced
>  by ~20%.  

Maybe the 3 turn arrangement gives tighter coupling, and/or a better
Z match?

>  2.4  The conclusion might be that if one wants to use a smooth 6" x 24"
>  toroid without a break-out point, one would definitely want a space-wound
>  primary, and with that spacing greater than mine--which averages ~.03"
>  betwen turns.  Either that or liberally slather on epoxy or the like and
>  hope that that substance withstands the voltage.  Is that what people do?
>   I'd hesitate to do it since a breakdown within that coating could be a
>  pain to repair.

I think CW coils have more of a problem with racing sparks for a given
toroid size and spark length than spark gap TC's.  I know that many
folks get long sparks using huge toroids with relatively small secondaries,
and do not get racing sparks.  This is little or no coating on the coil.

I noticed on my 36" spark tube coil, there was a lot of corona on
the primary, and I was using a breakout point.  With a big toroid,
the corona would have been much worse.  Yet, on my spark gap
coils, with even longer spark outputs, from the same coil, I didn't
have the corona problem.

In another test, I used a 7" dia by 9" tall secondary (28awg).  The
spark was reduced slightly, but i still got 34" sparks or so.  So
these were tube coil sparks that were almost 4 times the length
of the secondary.  Of course I use a breakout point.  This would
not have worked with breakout from a toroid.  (I may have posted
this before, I'm not sure if it was lost with the list-server crash.)

In any case, it would appear that tube coils of the typical design,
have to have a breakout point for longest spark output.  This seems
to be because of the double-tuned design, the resultant frequency
splitting, the changes in Q and bandwidth with breakout, and 
probably related Z matching factors also.  
>  
>  3.  Finally, a parenthetical observation of interest:  Since I can make
>  just 1 spark-event occur at a time if I wish, I can see that, often, more
>  than 1 spark will appear at the same time, i.e. during a given
>  pulse-burst, from the surface of the toroid.  As best I can tell by
>  closely watching the coil's E-field as displayed on the nearby
>  oscilloscope, such event is accompanied by a very sharp drop in the
>  E-field, at the instant of break-out and only on a negative half-cycle of
>  that field; never on a positive one.  Subsequent to that very sharp,
>  apparently negative-half-cycle, reduction, the E-field diminishes
>  uniformly, as expected, and is flat for the remaining duration of the
>  pulse-burst.  Anyone care to explain that?

The large drop in e-field with two simultaneous breakouts may 
just be due to the extra resistive streamer loading of two streamers.
I have no idea about the negative half-cycle thing, but it's interesting.
I notice that my pulsed coil with a point on top also sometimes
creates two sword-like sparks instead of one.  Maybe this is also
caused at a negative half-cycle breakout?

Regarding what you said about the spark being basically unchanged
with the 3 turn secondary.  I'm not sure what you mean.  You also
say above that the spark was the same, but mains current was
20% lower, which suggests better efficiency at least overall.  Can
you raise the mains current to what it was with the 2 turn coil, and
see how the spark behaves?

I wonder how long the spark would grow from a sharp point sticking
out from the toroid's edge?  The spark would not be as thick, but
may grow longer?

John Freau

>  
>  Ken Herrick