High Frequency Apparatus Page 97

ONE-HALF KILOWATT TRANSFORMER OUTFIT 97 3 BATTERY ZINC o 7"- Fig. 14. Simple zinc spark gap composed of three units of .01 mfd. each connected in multiple. Each unit is formed by coating both sides of 8 x 10 photographic negative glasses with 6 x 8 in. sheets of tinfoil, and assembling ten of these plates into a bundle as shown in the illustration. Lugs are brought out alternately first to right and then to left in the usual manner and these lugs soldered to a common connector on either side of the unit. The spark gap, Fig. 14, is simple in construction. This design is quite satisfactory, however, for experimental work on small-powered outfits. The electrodes are of battery zinc, ¾ in. diameter. A single zinc cut in two will answer well. The electrodes are held in supports of brass rod, suitably drilled and held upright upon a base that should preferably be of marble. If marble is not available, hard wood will answer. Slate should not be used as the minute metallic veins found in some varieties render the substance unsuitable for this purpose. Connecting and Using.-Fig. 15 shows how to connect the apparatus. The spark gap is placed across the secondary terminals of the transformer. The condenser is