High Frequency Apparatus Page 74

74 HIGH FREQUENCY APPARATUS 0 Wind with 1000 turns of No.22 enameled wire 72 turns per layer 14 layers deep Small choke coil 3" Fig. 4. Small choke coil in detail simple to build, and, as we have already noted, it is universal as regards current supply. The Interrupter.-This is the one weak point in the apparatus. While large and elaborate rotary contact breakers are more reliable in operation, they introduce too much weight and cost in an outfit of this nature. The next best is probably a simple vibrating interrupter with massive contracts similar to that shown in Fig. 3. The posts for the interrupter should be of generous proportions as the drawing indicates. The stock is of 3/4 in. square or hexagonal brass rod. The latter is preferable if the worker is possessed of a lathe as it may be conveniently gripped in the universal chuck for cutting, facing off and drilling. The spring should be of phosphor bronze; the thickness is preferably in the proximity of 1/32 in. At one end of the spring is screwed the armature of soft iron or cold rolled steel rod. This is simply formed by cutting off a 3/8 in. piece of ½ in. rod. A hole tapped into the armature takes the short length of 8/32 threaded rod that serves to hold the silver contact and armature to the spring. The contact is cut from a length of in. pure silver