Flat Spiral And Solenoid Combination Coil

To better understand Nikola Tesla's view of physics, I built a Tesla magnifier coil modeled after his Wardencliffe project.  I want 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 is wound with 21 gage wire.  A 4.5" OD PVC pipe jacket was placed over the windings and sealed at both ends.  The space between the jacket and the windings was filled with transformer oil.  This jacketed coil has absolutely no corona.  An interesting side effect is that a very strong static charge develops outside the jacketed coil for the full length of the PVC.

The flat spiral coil is the Chiron flat spiral coil mentioned on other pages on 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 the 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 heating.

This coil was set up with an eight-point static gap with compressed air quenching, utilizing only three gaps.  It works just as well with a single static gap that is magnetically quenched.

An oscilloscope, signal generator, and voltmeter were used during the coil testing to determine the resonant frequency.  In this setup, the ground of the oscilloscope and the signal generator were connected to Earth's 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 solenoid or flat coils, a combination coil has a single tune point, and it registers as a sharply dipped voltage 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 between 6 and 7 turns.  When the coil was fired up, the tuning point was where it was calculated to be.

This arrangement was unusual because streamers would emit from the terminal when the primary was set at less than 6 turns.  And when the primary was set for more than 6 turns, streamers would emit from the terminal.  But when the primary was set to an 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 brightly 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 solenoid's top to the flat spiral's outside.  The BK Precision 875A LCR meter gave 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 21.43 mH.

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 8 mH to 18 mH.  With the meter still connected, I shut off the power to the house.  The reading was steady at 21.9 mH.  When I turned the power back on, the reading was between 8 mH and 18 mH.  It is apparent that this coil combination is very sensitive to EM radiation.