The Turn Of The Century Electrotherapy Museum
(C) Jeff Behary 2010 

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Testing a Pancake Coil under Cast Silicone and Paraffin Oil

For this crude test, GE615 Silicone was used.  When mixed properly under vacuum it remains optically clear.
As seen, I didn't mix it properly...need a vacuum pump and oven.  Until then, "this is just a test"...
.024 mfd was used for these tests, 4kV.

Sectional View of Secondary Coil, Dimensions In Inches

Low power

On increasing the voltage and power, arcs start to form in air bubbles along the turns of most resistance (outer turns).
While the voltage is much higher in the middle, the resistance is less and arcing on the outer turns is typically witnessed,
though contrary to what most would imagine!  

This sparking is occuring where an imperfect seal was made between wax and silicone...

Also note the track starting to form on top of the coil...

Sparks continue, but tracks do too!

So, next test involves hacking off the top of the silicone casting

and replacing it with paraffin oil

Its an oily mess, but works better!  Removing air helps a lot!!

Roughly 5" discharge.  With a closer-coupled primary coil, this could easily produce 6" arcs or greater...

...which is a lot, considering the distance from innermost to outermost turn is only just over 1 1/8" !!

More to come!

(C) Jeff Behary, 2010