High Frequency Apparatus Page 50

50 HIGH FREQUENCY APPARATUS are theoretically correct in design. The proportions for cones may vary from a perpendicular equal to the diameter of base to a perpendicular 1.5 times diameter of base. The latter is better for long sparks. The windings of cones should contain from 100 to 500 turns of wire for short and thick, or long and compartively thin sparks, respectively. For the very closely coupled coils such as the pancake form, where the winding is in layers, and the coil sealed in, the number of turns may run up as high as 1500 to 2000 turns. The coil is of comparatively small diameter in this event. The layers of wire should never be very wide as the insulation will not hold up. The conductor for the secondary windings of all types of oscillation transformers should be of soft, pure copper wire. The insulation may be of cotton or silk but not of enamel. The use of the latter for high frequency secondaries has given the author great disappointment in the construction of several large and comparatively expensive coils. The insulation on the wire is of no value whatever except to provide a mechanical separation for the turns 3 a Fig. 5.-Showing proportions for Tesla and Oudin secondaries of any desired size