High Frequency Apparatus Page 108

108 HIGH FREQUENCY APPARATUS not so long; the comparatively low potential secondary is cheaply and easily built and insulation difficulties are lessened materially; for electro-therapeutic work, the quenched gap in connection with the low potential transformer gives a current of very high milli-amperage which is of value in cases where the blood pressure of the body must be reduced by auto-condensation in a short time. The instrument to be described is of 2 k.w. capacity and it delivers a secondary current at a potential of 2500 volts. The power factor is about 85 per cent. and at full load the primary of the transformer draws 23 amp. from the line on a 110-volt circuit. The winding specified is for 60cycle circuits but the data for other frequencies may be calculated as described on Page 27. As the construction of transformers has been covered so thoroughly in preceding chapters, no attempt will be made to cover the method of procedure. The core of the transformer is 3 in. square in crosssection and the core irons are to be provided in two sizes, i. e., 3 by 8 in. and 3 by 12 in. Each leg of the core will require 130 irons to build up the required three inches and accordingly 360 pieces of each size of iron will be required for the core. The core iron weighs approximately 94 lbs. for this transformer. This core is generously proportioned and the instrument may be overloaded to a considerable extent without ill effects as the core is not worked nearly to the point of saturation on a 60-cycle circuit. The primary winding consists of 152 turns of No. 9 D.C.C. magnet wire wound on a round form. As the winding space on the core is 5 in. the primary coil may be 4½ in. in length overall to provide the necessary ½ in. of space on either side for insulation. The winding may be tapped at the 125th, 135th and 145th turns if it is desired to have a convenient means of over-loading the instrument. When