RE: How to Tune a Flat Spiral Coil

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

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Bart,

>Two things here: First, this sounds like it's "out of tune", similar to the
situation on a helical where an out of
tune coil causes racing sparks. Which to me indicates that it "is tuning".
It's simply out of tune. The secondary should still ring at it's own
frequency. If I'm mistaken, hopefully someone will correct me.

You may be correct.  I don't have enough data to fully support my opinion of
my observation.  I can add, however, that when my flat spirals are out of
tune the spark gap cuts out during operation for a few seconds at a time.  I
didn't run the coil long enough at 2.5 turns to conclusively say that the
spark gap wouldn't have cut out, but it didn't during that time.

>Second, I'm amazed you arc'd through the 1/4" plexiglas. There "must" be
some very high voltages present. Curious, I would imagine the arcs point of
origin through the Plexiglas was near the outer windings?

Yes, the arcs occurred near the outer windings of the secondary.
Particularly the arcs occur at the three points where the three leads exit
the secondary.  I assume this is due to the weaker dielectric.  Although the
outer leads exiting the secondary have 1/4" of hot glue on them, the rest of
the coil is covered with 1/4" Plexiglas.  So there is already 1/2" of
Plexiglas between the primary and secondary for most of the coil surfaces.

Dave