Nikola Tesla Books
192 HIGH FREQUENCY APPARATUS The core may then be set aside to await the primary and secondary windings before having its magnetic circuit completed with the remaining sheet iron strips D. For winding the secondary, a form of square cross section similar to that shown in Fig. 7 should be employed. This form may be of wood and solid in construction. The corners should be slightly rounded. The dimensions are given in the drawing. After the form has been mounted in the lathe between a spur-chuck and a center, it should be covered with a winding of a single layer of cord. Over the cord is placed a 1 inch thickness of oiled paper, then a layer of inch flexible mica and finally 4 or 5 additional thicknesses of paper. Each layer of this insulation should be tightly secured with thick shellac in order to make a solid core or base upon which to place the secondary winding. The latter is done in two sections, wound in opposite directions and having their inside ends joined together. This end is attained by first winding one section and then reversing the secondary core upon the form and starting the remaining half of the winding by joining the wire from the spool to the starting end of the first section. It will be noted that the two sections of the winding are divided by an insulating shield of mica which is cut to fit over the core and placed in position when the first section has been completed. The starting and finishing ends of the winding are soldered to pieces of thin copper ribbon about 4 inch wide. After both sections have been completed the finishing layer in each should be covered with oiled paper to a thickness of 1 inch. The secondary winding consists of 3,525 turns of No. 25 enameled wire wound 75 turns per layer and 41 layers deep in each half of the secondary winding. Each layer
