Re: A coil tuning aid

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Weazle wrote:

> Most of us tune our coils by watching for the longest streamers...
> ...I reasoned that by measuring the current in the ground lead
> of the secondary, I could use that to optimise the tuning.

That ought to work really well.

You might note the tap setting when tuned in this way for max probe
reading while breakout is occuring.  Then run at low power, below
breakout, and find the new best tuning point.

Presumably, relieved of its streamer loading, the highest base
current will occur with fewer turns on the primary than when the
secondary is loaded by the extra capacitance of the streamers. 

>From the amount by which the tuning shifts, you might be able to
infer roughly what fraction of your secondary current is circulating
through the streamers.

Further, if the VTVM averages over a few hundred milli-seconds or
so, you might try plotting a graph of VTVM reading verses variac
setting, tuning and adjusting the gap as necessary to max out at
each setting.

Below breakout, you should get a straight-ish line.  Above breakout,
it may level off a little, in which case, from the amount of leveling
off, we might have a shot at working out what percentage of your
RF energy is dissipating in the streamers.  This might be confounded
by the non-linearity of the primary gap, but the approach is similar
to the lamp testing discussed recently.

I'm surprised that coilers don't make more use of base current
measurements for tuning, etc.  There's a lot of info in that signal.
--
Paul Nicholson,
Manchester, UK.
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