Thank you both, I think I know where to go from here on my current build.
My project is a larger bipolar than I have built to date. Secondary is 3.5"
dia. X 24" with .015 mag wire. By the time I built the primary it was 6"
long and I was getting "runners" on the secondary. I think my fix will be
going to a flat spiral primary.
Doug
On Thu, Oct 15, 2020 at 12:06 AM jimlux <jimlux@xxxxxxxxxxxxx> wrote:
> On 10/14/20 6:34 PM, Gary Lau wrote:
> > It also needs to be said that highest coupling is not the goal - more is
> > not necessarily better. Performance will generally increase with
> > increasing coupling, until an ill-defined threshold is reached.
> Increasing
> > coupling beyond that point will result in what's called "racing sparks" -
> > sparks across portions of the surface of the secondary coil that can
> > quickly destroy the secondary. You need to design the coil in such a way
> > that the distance between primary and secondary can be experimentally
> > adjusted to vary the coupling, typically by raising the secondary. For
> > most coils, using a flat spiral primary provides adequate coupling when
> the
> > plane of the primary is near the bottom end of the secondary.
> >
>
> ANd the flat primary also serves as a sort of counterpoise to make the E
> field uniform between topload and primary.
>
> Go back in the archives and you'll see all sorts of primaries,
> solenoids, inverted cones (I did that one), and flat spirals.
>
> The advent of modeling tools (like Inca and JavaTC) that could
> *calculate* coupling and fields pretty much drove the "make it flat" -
> except for ones requiring high coupling (DRSSTC, for instance), where
> solenoid primaries are popular.
>
> There's not much you can do with a conical primary that you can't do
> with a flat or solenoid, with some control of the spacing.
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