Nikola Tesla Books
20 20 HIGH FREQUENCY APPARATUS LEAKAGE Fig. 4. Typical closed core transformer arranged for power and lighting circuits. Close coupling of primary and secondary prevents excessive drop in secondary voltage when load is applied literally blew out the arc as soon as it formed; and various devices which mechanically separated the electrodes to a point where the arc was extinguished. The most familiar form of the latter device is the common rotary spark gap. As the work progressed, the experimenters discovered that by placing an impedance coil, consisting of a single winding of copper wire on an iron core, in series with the primary of the transformer, the arcing was materially lessened and the various blow-out devices were rendered unnecessary to a certain extent. This procedure is illustrated in Fig. 5, which shows the impedance coil in series with the primary of the transformer, the windings of which are closely coupled. This was the first step in the direction of the celebrated "Type E" wireless transformer which was patented by Mr. Melville Eastham of the Clapp-Eastham Company, and which has been copied in various forms by dozens of manufacturers since its introduction. The design of the Type E transformer introduces the very quality that the makers of power transformers seek to avoid, namely, magnetic leakage in the core. When the secondary of such a transformer is short circuited by
