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RE: variable inductor primary tuning (fwd)

---------- Forwarded message ----------
Date: Mon, 23 Jul 2007 10:26:28 -0500
From: David Thomson <dwt@xxxxxxxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: variable inductor primary tuning (fwd)

Hi Scott,

> If one was building a small TC or other resonant circuit and wanted
> make a fixed primary (without taps) would one be able to put some
kind of 
> variable inductor in series with the primary coil, and vary the
tuning in 
> this manner?  I would assume this would not be the most efficient
way, but 
> does it actually work this way or not.  Thanks.

I just happen to be building one right now for the same purpose.  I
believe I read that Tesla built a primary-tuning variometer using two
flat spiral coils joined at the center leads, sliding along a
conductive pipe or rod.  He apparently needed this to tune a three
coil system.  The flat spiral windings should be wound in opposite
directions from each other to gain maximum variability in inductance.

There will be a slight loss in power, but that should be made up for
with better resonance. Increasing resonance decreases losses in the
secondary circuit, which increases the available power to do what you
want to do.