Nikola Tesla Books
HIGH FREQUENCY APPARATUS LEAKAGE Fig. 8.-Type E transformer with tongue of iron to increase magnetic leakage between windings The transformer core in each case should be of thin sheets of silicon steel, .014 in. thick, and made expressly for use in transformers and other alternating current apparatus. In the directory of materials, in the back of the book, the prices of this steel will be found. It is practically as cheap as the so-called transformer iron and, if results count, it is much cheaper than stove-pipe iron. The construction of the core is simple. The silicon steel can be bought in sheets or, preferably, in pieces cut to size and ready to assemble. The rectangular pieces are placed one upon the other to make piles of the required thickness for the assembled core and then firmly gripped with a binding of tape. The windings are made on simple wooden forms, either in a lathe or else on a hand winding device. The winding is invariably that known as the layer method. The "pie" winding, described in so many of the older books on radio construction, has been tried out thoroughly by the author and by many of his colleagues; the result is a wholesale denunciation of it, bag and baggage, as it were. True, a modification of the pie winding is seen in many of the designs presented in this book but the pertinent fact is that the directions do not call for an annulus of wire, held together by wax, and with the turns laid on any-which-way.
