Subject: Secondary Progress
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Wed, 11 Oct 1995 05:30:00 GMT
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Quoting Scott Myers <102505.61-at-compuserve-dot-com>:
> You wrote;
> Since you are winding an eight point five inch (8.5") diameter
> secondary coil, your secondary inductance is going to be nice
> and high. As such you will not need a very steep angle of
> inclination in your primary winding to get critical coupling.
> Fifteen degrees of slope, rising from the inside turn of the
> primary (which is level with the bottom turn on the secondary)
> up to the outside turn, should put you right in the ballpark
> for good coupling coefficients. RQ
> I thought you advocated using flat primaries with coils over a
> certain diameter. This 8.5" unit is pretty big.
You are correct if this coil is going to operate a pole pig power
levels with high quality tank circuit capacitance and well
quenched spark gaps. While the coil may certainly end up in that
configuration, it will most likely start out at 2 kVA or under
with a neon power supply. I would rather have a coiler build a
system that will couple a bit snugly at lower power (perhaps with
cobbled together caps and gaps) which allows better power
processing efficiency, than see someone disappointed with the
initial fire up and tune-in performance. Nothing is worse than
seeing the new coil project perform weakly when first fired up
and tuned in, regardless of the reason.
As proficiency, tune, and peak powers improve; the coil will
over-couple. The solution is to raise the secondary a couple
of inches, which is easily accomplished.
I guess what I am saying is that the coil will "critically"
couple at lower powers, and can be adjusted to critical coupling
when it is peaked out. I feel this is better than a system that
is coupled too loose at lower powers (or with less than prime
quality capacitors and spark gaps in the tank circuit), where
only major changes in the coil designs will improve coupling
coefficients. At lower powers typical of a neon bank, and with a
decent sized toroid, a 15 degree primary will work beautifully.
If the coiler were going to throw a pig on this coil to start,
and already had plenty of first rate capacitance and lots of
experience with high performance spark gaps, I would advise
building a flat primary with no angle of inclination.
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12