Off-Axis Primary Tuning

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Original poster: "Justin Hays by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hi All,

There was a post here a few days ago (Nov. 27th) regarding the use of
off-axis inductors for tuning a TC. I'm a little late but did want to
add my 2 cents here.

Anyhow, yes! If you have "run out of turns" on your primary, you can
add a coil in series with your primary (on either end, it doesn't
matter) to get things back in tune. My friend Aron and I have used
this technique tens of times to tune larger toploads.

Aron purchased a variable inductor at a hamfest last year, the
conductor itself was 1/4" tinned copper bar, wound flat (pancake
primary style) on a 12" phenolic baseplate. There was an arm and
roller that made contact with the copper, and brought it out for a
separate connection. There was also plenty of separation (40kVDC
worth probably) between each end of the inductor, and we both
speculated that a motor-drive arrangement would work quite well. It
would have made a beautiful primary had we removed the mechanical
stuff.

When I first implemented the off-axis technique, I wondered about a
possible decrease in efficiency due to the extra copper and unused
inductance. It turns out that the decrease (if any) was not
perceivable, but actually resulted in better sparks if a larger
topload was tuned.

Examples of off-axis inductors:

1. Bare copper wire wound around a section of PVC pipe
2. Insulated wire wrapped around something as a form, then
tie-wrapped together to hold it all. This makes it difficult to tap,
but it's very quick and simple!
3. Another primary coil in series ; )

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P.S. Lot's of new stuff on our website!

Take care,

Justin Hays
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com

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Justin Hays
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com