RE: Tap tunable secondary

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>

Hi Terry:

Here's an untested idea.  Make the secondary in two equal but disjoint
halves, wired in series.  The separation between the two may be adjusted
from zero to a couple of inches, which would vary the coupling and mutual
inductance between the two, effectively making the total Lsec continuously
variable.  Unknown is what effect the discontinuity between the two halves
might have on corona, but perhaps a very small field-shaping toroid could
be placed at the joint.  Shorted turn???

Regards, Gary Lau
MA, USA

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

I am having problems tuning my CW coil.  It is run off a variable frequency
900 watt, 325 to 375 kHz, industrial plasma power supply.  I can wind
matching transformers on big 3C8 cores to fix input impedances, but the
frequency is a problem.  It has a master oscillator frequency control so it
does not track with fancy feedback, PLLs or anything like that.  But I can
adjust the frequency by hand.

The problem is the secondary frequency.  If I place different top loads on
it (like the power arc tonight) It tends to drop the optimal resonant
frequency too low and I can't get to the optimal frequency given the power
supply's range.

So I was thinking of making a new secondary with tap points on it so it
could be taped at different frequencies.  About 5 inches on one end will
have a bunch of wire loops coming out.  I don't know if it would be best to
put these taps at the top or bottom of the coil.  I am worried about
autotransformer action and other problems with the unused windings.  

Any thoughts on this are welcome.  I don't remember anything like this
being discussed before but maybe the long time tube coilers have run into
this and have some ideas.  I want to pump the full 900 watts forward (plus
250 reflected if needed) into a power arc to see if I can make the sparks
Richie got.

Cheers,

	Terry