Re: Tuning Isis and Osiris

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

Original poster: "Nicholas Field by way of Terry Fritz <twftesla-at-qwest-dot-net>" <nick.field-at-hvfx.co.uk>

> I finally got the primary coils tuned in.
> I connected the two primary coils in series with a 500 Ohm resistor and
the
> signal generator. I put my good Tek 2246 across the resistor. The coils
are
> spaced around 9 feet from eachother.
> Tuning is from the bottom up with Cp. I'll send you an attachment if you
> wanna
> see the circuit. I spent several daze trying to dip the circuit with a RMS
> digital mA
> meter in place of the resistor and scope. I finally read the fine print
for
> the meter to discover that
> the darn meter poops out at 100 kc. This was causing all sorts of spastic
> parasites
> and artifacts in the measurements. I also had the sig gen in parallel
until I
> began
> to suspect that I might be loading down the generator excessively.
Learning
> slowly.
> I tuned the coils by clipping the leads from Cp onto the coil, using the
same
> spot on each coil. I then adjusted the sig gen to find the arbitrary F
res.
> If too high,
> I added Lp, and if too low, I removed turns. I kept twiddling until I
zeroed
> in on
> the exact spot where F res for the primaries is 151 kc = F res for the
each
> secondary with its topload.
> Can you find anything in all this where I am still screwing up something?

Sounds good to me.  Although it is important to remember that the 'ion
cloud' and streamer load add an enormous amount of top capacitance
to the secondaries, so the operating and static tune points may differ
considerably.  A meaured tune point will give you a good starting point,
but expect to have to tune out further for maximum arc length.

> You were certainly correct when you said that tuning a twin coil is the
most
> gul durn
> cantankerous thing ever. I thot it would be simple. Now I gotta put the
beast
> back together and fire it up for the 100 inch sparks.
>
> Q:
> What's happening here? F res for EACH secondary is 151 kc. I have tuned
the
> two primaries in series and across Cp. That's how they are connected in
the
> twin. But
> I have tuned the two primary coils in series so the TWO of them resonate
at
> 151 kc. Then we
> are going to wrap each primary around its secondary with the two primaries
in
> series
> and across Cp. Is each primary resonating at 75.5 kc? The primaries are
far
> apart and the bases of the secondaries are tied
> together and grounded to the power line ground. And to make things even
> funnier,
> We will have to find the electrical zero point by trial and error. All
very
> funny, I wish I understood the joke.

You'll get the joke about the same time you see those 100" arcs!

The primaries form a series resonant circuit at 151kHz. Although on this
basis I have yet to, satisfactorily, explain the apparent 'tuning' of
individual secondaries except perhaps as a coupling adjustment rather
than an actual tuning process.  I would be interested in any modelling
work that proves/disproves this hypothesis.
The grounding issues can be easily solved by connecting to an RF ground -
mains ground is not a good idea.

Safe Coiling
Nick

_______________
Nicholas Field
Director,  HVFX
www.hvfx.co.uk

>
> Happy day,
> Ralph Zekelman
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