Nikola Tesla Books
148 HIGH FREQUENCY APPARATUS From the working drawing, the core is seen to be built up from pieces of sheet iron or silicon steel .014 in. thick and 74 in. long by 2 in. wide. This is for the 60-cycle transformer. The same general directions apply in the case of the other frequencies, therefore the description will be confined to the one only. In all, 460 pieces will be required. If silicon steel can be obtained from some transformer manufacturer it should by all means be used as it is not expensive and its permeability is very much higher than that of ordinary sheet iron. The core irons are laid up alternately in piles until each has assumed a thickness of 2 inches, after which end pieces are fitted in the spaces left in the ends of the piles as shown in Fig. 2. Friction tape should be wrapped around the pieces of iron to hold them in place. The primary coil consists of 350 turns of No. 12 D. C. C. magnet wire wound upon a form which will give the opening in the coil a diameter of 3 inches. The primary may be wound to a length of 4½ inches and after it has been removed from the form it should be carefully taped. The secondary is wound in 2 sections, each containing 16,000 turns of No. 34 enameled wire. These sections also have an opening 3 inches in diameter to permit their being placed over one leg of the core. The winding is in 80 layers and has 200 turns to each layer. A strip of oiled paper 2 inches wide separates each layer of wire from its neighbor and as the 200 turns will occupy a space of approximately 1½ inches, it is obvious that a space of 1/4 inch will be left as a margin on each side of the paper. The starting end of the winding of each section is soldered to a strip of thin copper ribbon which extends beyond the edge of the coil. The finishing end is likewise connected to a piece of ribbon which should come out on the opposite side to that of the starting end. The final layer
