My first TC was ‘discovered’ while running a spark spectroscopy project (above) in high school 40 years ago. This used about 10 kV from multivibrator excited dual ignition coils through 10 turns of an air cored radio coil to quench it. The other end of the 130 turn coil developed a corona visible in the dark spectroscopy room. It was a truly amazing sight.
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The spark spectroscopy setup in use (but not in operation as a Tesla coil). The original high voltage setup with the spectroscope shown open and the HV diode, air cored coil and cap made of 6 x 0.0033 uF 3 kV ceramics in series to give 550 pF. The spark gap with clips to hold the metal being examined spectroscopically is also shown.
Somewhat remarkably, this was an inadvertent Tesla coil complete with spark gap, tank cap and air-cored coil AND it worked unintentionally.
Above shows a reconstruction which took about an hour to make in May 2005. It uses the same size cardboard former as the old one 45 x 100 mm which had to be reinforced with PVC. (Toilet rolls are not as strong in 2005 as 1972) The wire gauge is 0.40 mm (prev 0.6 mm) and is wound to 130 turns with multiple taps between 10 and 20 turns. The caps were 6 x 0.01 3 kV = 1600 pF (prev 550 pF) and power supply was my SIDAC driven twin ignition coil setup. Spark gap was about 2mm as anything higher gave racing arcs!
Reproducing my Tesla coil discovery was harder than the original. Spark length was only 1 cm but corona was visible with dark adapted vision.
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Briefcase Tesla coil
Mini Tesla coils
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Photo Date: Jan 19, 2003