High Frequency Apparatus Page 76

76 HIGH FREQUENCY APPARATUS not come quite out to the end of the layer of insulating cloth; this affords ample protection to the end turns which are subjected to maximum potentials. The larger of the coils is shown in detail in Fig. 5. The core is 634 in. long and ½ in. in diameter. The winding is of No. 20 D.C.C. wire wound two in parallel. Each layer comprises 84 double turns and there are 14 layers in all. The same rules as to insulation apply as in the case of the small coil. The Condenser.-This is of the glass plate variety in the present design. If the builder cares to invest in mica plates of the same size, he will effect a material saving in space and weight. The glass to be used is of the variety known as “lantern slide cover glass." As the name implies, the glass is used to cover the photographic positive in a lantern slide. The cover glasses are thin and perfectly free from bubbles and the usual defects. They may be purchased from almost any photographic dealer and the standard size is 3 x 4 inches. For the condenser at its maximum capacity, 200 plates of glass will be required. While this large capacity is not always in use, still it is essential for certain classes of work and it should therefore be provided. The conductor for the condenser is heavy tin foil. This comes in sheets 6½ x 8½ in. and 27 sheets weight a pound. For our condenser 200 pieces are to be cut 3½ x 44 in., and for this operation a photo trimmer is well adapted; lacking this, the foil may be placed on a large sheet of glass and cut with a sharp knife. The condenser is to be assembled into 20 units of ten plates each. This makes for convenience of adjustment. Each little unit will have a capacity of approximately .005 mfd. and the entire condenser therefore reaches .1 mfd.