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Two layer primary

I would like to rebuild my primary as a two-layer flat pancake.  The reasons
for this are:

1) I am also increasing my secondary inductance so that I can
correspondingly increase my primary inductance to achieve a higher surge
impedance and hopefully further lower my gap losses.

2) The required higher primary inductance would make a single-layer primary
too large in diameter to fit the confines of my base assembly.

3) By making a two-layer primary, the same inductance can be achieved with
fewer feet of tubing, thereby further lowering primary losses.

I'm drawing a blank on how to begin this construction.  The two layers will
be joined at the center, so the two terminals will be at the outside of each
spiral.  This means that the full primary potential (and much more if there
are unused turns!) will be present across whatever gap separates the two
spirals, so extra care must be taken to insulate against surface flashovers.
Obviously a Lexan plate must be built between the layers, and there can be
no holes through this plate, as I suspect a flashover will find such holes.
The no-holes rule complicates plans to mount the two spirals.  I don't like
the idea of gluing - it's potentially messy, and mistakes and changes are
made and glue is kind of permanent.  Short of using two back-to-back
insulating disks with holes that are offset, I'm short of good ideas.

Has anyone done this before, and can you point to any URL's that illustrate
how it was done?

Gary Lau
Waltham, MA USA