Tesla Coils Resurrected

You Can Get 24-inch Spark from Oudin High Frequency Coil

This article describes the complete construction of an Oudin and all the other incidental apparatus needed for its effective operation; data being given for the building of the high-voltage condenser, rotary spark gap and exciting transformer. Spectacular demonstrations can be given while you play with this harmless current of extremely high voltage and frequency.

The Oudin high-frequency coil is a blood-brother of the well-known Tesla coil and in fact, the only real difference between them lies in the manner in which the primary and secondary windings of the two coils are connected. In the Tesla coil the secondary is not connected to the primary, and the primary winding is centered over the secondary. In the Oudin coil, the lower end of the secondary winding is connected to the primary in the manner shown in the accompanying diagram.

The Oudin coil is particularly suited to lectures and demonstrations as a veritable “tree of sparks” leaps from the ball atop the coil, with a loud crackling sound!

In other words, the voltage rises to a maximum at the upper or free end of the Oudin secondary; causing a single-pole “crashing” spark discharge to take place about the ball shown in the picture. Sparks 18 to 24 inches in length “leap out into space” in a very spectacular fashion, especially in a darkened room; and vacuum tubes may be lighted by holding them in the hand, sparks allowed to jump to a piece of metal or wire held in the hand and numerous other startling experiments performed.

For exciting this Oudin coil, a 60-cycle transformer of the usual step-up type and having a primary designed for 110 volts 60 cycle A.C. and a secondary delivering from ten to fifteen thousand volts or more at one kilowatt input, is desirable. Heavier sparks will be produced if a 1 1/2 to 2 K.W. exciting transformer is available; but very good results have been obtained with a 1 K.W. transformer.