The Precise Measurement of Output Potentials in a Tesla Type Air Core Resonant Transformer System

(continued)

Experimental Techniques

After applying these calculations to their coil systems, some experimenters will be rather disappointed with the results. A Tesla system producing a high frequency discharge of 16 feet is actually only producing one million volts. The actual D.C. pulsed discharge from such a system is only 5 feet in length. Once this initial corona path is established, the next pulse conducts to this ionized path as if it were an extension of the discharge terminal, and then discharges an additional 2-3 feet. The actual additional length is dependent upon the energy in the system (1/2ce²).

A Tesla system produces high pulse repetition rates, and the spark actually appears to “grow” in length within 200-800 microseconds after initial application of power to the system. This “antenna phenomenon” increases as the power to the system increases. High speed photography reveals the initial discharge in the first 10 microseconds represents the true output of the system. We, at Resonance Research, Inc., are currently investigating this “antenna growing” phenomenon in greater detail, and will present a paper on this subject at a later date.

The only accurate method of easily determining the approximate output of a Tesla oscillator is to rectify the output of the power supply transformer, and then pulse the oscillator system with direct current at periodic intervals:

Some of you might cringe at this procedure as it sounds expensive, but it's not! A high voltage diode is available from Varo through local electronics jobbers for $3.36. Ask for Varo VG-20. This diode will rectify 20 kv PIV at 40ma, and will handle the pulsed mode output of even a 60ma neon sign transformer without any problems. Varo recommends oil-immersing or epoxy-encapsulating this diode at potentials above 10kv. However, a piece of heat-shrink tubing snuggly fitted over the diode will hold off up to 20kv without incident.

Resistor (R₁) is a 10 watt high voltage resistor in the range of 20-50 megohms. The exact value depends on the capacitance in your capacitor bank, and the discharge rate you wish to pulse your system at. We usually calculate the rc value through the resistor to charge the capacitor bank to its firing potential every 2-3 seconds. This resistance also serves to limit the charging current in high powered systems. These special high potential resistors are available through local jobbers for around $10 per unit. If you are really on a budget you can substitute a series string of one watt carbon resistors encapsulated in epoxy.