The Turn Of The Century Electrotherapy Museum
(C) Jeff Behary 2006

Testing a modified "Jackson" Pancake Coil

Working with electrician Howard Jackson of the Swett & Lewis Company, Thomas Burton Kinraide developed "The Jackson Coil".  This was a thin flat coil that gradually rose in the middle to create a gradual Pancake-to-Conical Coil.  This allowed the use of a thicker wire (less resistance) and more turns than a traditional Pancake or Kinraide style Coil.  In this example, I wound a 7" OD .75" ID flat spiral coil with 1.5" wide paper interleaves made from several rolls of "cash register" paper.  It had roughly 200 turns.  The The flat coil was laid upside-down in a glass form - actually an inexpensive light fixture from a hardware store.  The outside of the glass was painted with a non-conductive red alkyd paint to simulate bakelite.  A Primary was wound on the outside that consisted of 3 turns of 12 AWG solid copper wire.  The whole glass container was poured with a very hot mixture of beeswax, rosin, and boiled linseed oil.  The output is quite interesting... 4000V and .016 mfd.

The brush discharges are 8" in length.  Kinraide and Jackson's original apparatus used a 30,000V transformer and a special patented spark gap.

Click here for a movie of the above coil in action!

Bottom of coil, showing Primary

Finished Coil

Induction-melted Wax and Rosin mixture!

(For those wishing to not to use wax and rosin, please look at the end of this page at the burned out version of this coil!)

(I tried to use a modern resin...apparently it didn't saturate the interleaves quite good enough...!!!!!)
(Wax and rosin works really well, even 100 years later.  No need to reinvent the wheel here for me!)