Re: Tube coils

In a message dated 99-03-03 05:35:05 EST, you write:

<< > Original Poster: Michael Tucknott <Michael.Tucknott-at-virgin-dot-net>
 > Hi all
 > Why is it that tube coils don`t use a torroid???
 > Thanks in advance
 > Mike Tucknott >>


That's a good question.

On my small tube TC (19" spark), I gain about 1" of spark output
when I add a 1.5" by 6" toroid and retune slightly as needed.  On
a larger tube coil (36" spark), adding a 3" by 10" toroid didn't help
the spark length.  In both cases, I installed a sharp metal spike
projecting well above the toroid to provide a spark emission point.

Since tube coil output is CW, the peak output power and voltage
is lower than spark gap TC's, so the spark may build up it's length
more by build-up from secondary Q, and ion trail heating.  The 
toroid is used not so much to delay breakout, but simply to supply
a capacitive load when used on a tube coil.  If the toroid on a tube
coil is too large, the operation of the coil can become raspy and
inefficient.  The toroid tends to increase the current in the spark,
and this may sometimes help the spark length a little.  But if
overdone, it draws a lot of extra power from the power supply and
can lower the overall efficiency, and may overheat the tubes.

John Freau