Richard's set

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Coherent Cortical Stimulator 


It all began during a late summer visit to Richard Hull’s physics laboratory in Richmond Virginia. I had been invited to meet with a group of experimenters for a day of fellowship, fun and food. A Tesla coil demonstration was scheduled for the afternoon.

After signing the guest book, I looked around the room. There, mounted on a stand in the middle of the laboratory, loomed a huge vertical coil capped with a large silver toroid. At its base was a circular spiral coil of copper tubing, shaped in the form of a shallow dish.

Though no energy flowed through its coils, it looked impressively powerful. The fun had begun, it was time to START THE BIG MACHINE! After donning ear protectors, lights were turned off and power was gradually applied to the primary circuit. As the transformers began to hum and the rotary spark gap increased its speed, lightning leaped further and further from the toroid. At peak power, the room was filled with tremendous lightning bolts striking the walls, ceiling, workbenches and floor. Florescent lamps glowed with an eerie light. Continuous lightning and thunder filled the room while ozone tinged the air.

It was an awesome sight and a memorable experience. (Frankenstein would have loved it.) Some time later, while thinking about the nature of Tesla’s ideas and his use of resonant circuits, the parallels with crystal set circuits suggested a somewhat unorthodox approach to crystal set coil design. The result is described and pictured below.


This crystal set consists of three separate circuits. They tune the antenna, detector and wave trap. The antenna tuner employs a capacitor (on the left) with a common rotor and two stators. One section is paralleled with the dished spiral coil and connected to the antenna. This circuit is then coupled to ground through the second capacitor stator. A second parallel tuned circuit (detector) consists of a single section capacitor (on the right) and the coil atop the vertical column. A third parallel tuned circuit (wave trap) employs the middle capacitor and the coil situated below the antenna coil.

Similar coupling is provided for the wave trap coil by positioning it along its support column.

Both the detector and trap coils are wound with 420/44 Litz wire, 30% turn spaced over polystyrene coil forms. The antenna coil is #16 silver-plated, Teflon coated stranded wire, 100% turn spaced on a Lexan form. PVC tubes support the antenna and wave trap coils. The detector coil is mounted on a plexiglass tube.

The capacitors are (NOS) Hammarlund brass types. The antenna and detector capacitors are isolated from hand capacitance and all are tuned with National “Velvet Vernier” drives.

The set employs dual galena detectors, mounted on a granite base for dimensional stability. Once a sensitive spot is selected, it holds adjustment. The small brass sphere on the granite base is connected to a quick-change diode mount on the underside of the wood platform. This provides a means of rapid initial tuning before switching to the galena or experimenting with different diodes as desired. The detector arm is a Philmore unit that can be positioned anywhere on its neodymium magnet base to easily reach any crystal.

An impedance matching transformer (100k/100), for sound powered phones, is mounted on the underside with dual audio jacks for shared listening.

Nylon spacers and polystyrene tubes provide isolation for the capacitors and wire “feed through” isolation from the platform which is sealed with several coats of polyurethane.

Four, 4” legs raise the set to a comfortable visual height for the dials and provide additional isolation for the coils.


During the DX Contest, comparison testing with my “big set” showed Nemesis II to be very sensitive. Very weak signals were heard but the band was quite crowded. Difficulty was experienced achieving the increased selectivity expected from Litz coils.

During initial concept testing with solid wire coils, minimum coupling was within range of maximum coil separation. Litz coils require a greater separation than solid wire coils to achieve this minimum coupling. With the new coils, excessive coupling limited Nemesis’s ability to achieve a clean separation on adjacent channel stations.

Removing the ground wire restored 10 khz selectivity but the cost was lower signal strength and an increased tuning interaction between the circuits. I was somewhat surprised it received as well as it did without a ground, but attribute this to increased coil coupling.

Overall, I’m well satisfied with the set’s performance and plan to replace the support tubes with longer units to realize its full potential. It was fun to build. I now have a rather unique “Art Nouveau” crystal set for visitors to experience and enjoy. Eventually, it’s destined for my grandson to play with.