Flat Spiral And Solenoid Combination Coil

In an effort to better understand Nikola Tesla's view of physics, I built a Tesla magnifier coil modeled after his Wardencliffe project.  I would like to give special thanks to Floyd Purcell who helped make the components for this coil.


The tall solenoid coil has a winding length of 48.125" on 3.5" OD PVC pipe and wound with 21 gage wire.  A jacket of 4.5" OD PVC pipe was then placed over the windings and sealed at both ends.  The space between the jacket and the windings was then filled with transformer oil.  This jacketed coil has absolutely no corona.  An interesting side effect is that a very strong static charge develops on the outside of the jacketed coil for the full length of the PVC.

The flat spiral coil is the Chiron flat spiral coil mentioned on other pages in this site.  It is 25.25" OD with a .25" ID radius.  A .25" threaded brass rod is molded into the center of the coil and provides the connecting point for the tall solenoid coil above.  The flat spiral coil is wound with 12 gage magnet wire and is covered with several coats of polyurethane and two coats of polymer coating.  Over the top of this coating are two .25" layers of Plexiglas that separate the flat spiral from the conical primary winding.

The primary winding is 8.25 turns of .25" OD copper tubing on a Plexiglas stand.  There is about .375" between windings.

The capacitor is two sets of multiple caps wired for .04µF and arranged in series for a total of .02µF.  The multiple cap assemblies are immersed in Plexiglas tanks of transformer oil to reduce corona.

The transformer is a 15KV 60mA NST with no protection circuits.  When this coil is tuned to resonance, the transformer operates for hours without the least bit of heating.

This coil was setup with an eight point static gap with compressed air quenching but only utilizing three of the gaps.  It works just as well with a single static gap that is magnetically quenched.

During the coil testing an oscilloscope, signal generator and voltmeter were used to determine the resonant frequency.  In this setup the ground of the oscilloscope and the ground of the signal generator were connected to earth ground.  The positive leads of the oscilloscope and signal generator were connected to the outer lead of the flat spiral coil.  The voltmeter was connected with the ground lead to the outer lead of the flat spiral coil and the positive lead to the terminal of the tall solenoid (the copper capacitance ball was removed.)

Unlike either solenoid coils or flat coils alone, a combination coil has a single tune point and it registers as a dip in voltage sharply between two voltage peaks.  This coil combination registered clearly at 145KHz.  There was no other resonance for this coil in the range of 1Hz to 1.1MHz. 

The primary coil was designed to have resonance at between 6 and 7 turns.  When the coil was fired up, the tuning point was where it was calculated to be.

What was unusual about this arrangement was that when the primary was set at less than 6 turns, streamers would emit from the terminal.  And when the primary was set for more than 6 turns, streamers would emit from the terminal.  But when the primary was set for exact tune, a few sparks would at first emit but then the coil would run continuously without emitting any sparks from the terminal.  All the power remained fully inside the resonator.

When fluorescent tubes were held in my hand they lit, and they lit quite bright when touched to metal surfaces in the surrounding area.  The larger the metal surface, the brighter the bulb would be.

During the coil testing, the inductance was measured from the top of the solenoid to the outside of the flat spiral.  The BK Precision 875A LCR meter was giving a wide range of rapidly changing inductance readings.  The readings varied from 4mH to 30mH.  The individual coils did not have this problem.  The flat spiral coil measured 4.75mH from the outer lead to the center of the flat spiral coil.  The solenoid coil measured 16.68mH from the bottom to the top of the coil (no capacitance or any other connections were made to the coils during the test.)  This gave a total added inductance of 21.43mH.

During a recent thunderstorm the power went off in my lab.  So I measured the inductance from the outside of the flat spiral to the top of the solenoid.  This time the inductance measured a steady 21.9mH.  When the power came back on I measured the inductance again for the combination, and this time the inductance reading was everywhere from 8mH to 18mH.  With the meter still connected I shut off the power to the house.  The reading was steady at 21.9mH.  When I turned the power back on the reading was once again between 8mH and 18mH.  It is apparent that this coil combination is very sensitive to EM radiation.