Re: 2 layer primary puzzle

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

Original poster: "James T by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jamest2000-at-att-dot-net>

 Thanks to ALL you guys!
I got to play with my 2 layer primary tonight. I was able to get the proper
inductance by connecting the
top/inner to the bottom/outer turns. I also fliped the bottom coil and that
also did the trick, exactly
as described.
 I thought it was interesting that I could rotate the top coil and this
would vary the inductance quite
a bit. It would be a mechanical challenge the make an adjustable primary by
rotating the two primarys
about the axis.
 Anyway I am back in business on this project. Thanks for the help. Malcoms
comments below are exactly
why I went for the dual primarys.

> Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
>
> Hi Harvey,
>            This seems like an incredibly complicated reply to a
> rather simple problem ;) :).
>      FWIW, I routinely used stacked spiral primaries, mainly because
> it costs a lot less for copper pipe to score the same inductance as a
> single spiral. It is also far more compact. The next primary I build
> for an impending 12" coil will have three layers.

> Thanks to mutual
> inductance between the layers, you can score around 70% more
> inductance using two layers using the same length of pipe and
> allowing for some clearance between the layers (e.g. an acrylic sheet
> with a centre hole).

Measured top pri         40 uh
Bottom coil                 27uh
Both                          113uh

Now thats some mutual induction! This is at 1.25" space between.
Best Regards,
 James