High Frequency Apparatus Page 127

PHYSICIANS' OFFICE EQUIPMENT 127 Each unit of the condenser is composed of 10 plates of 8 x 10 photographic negative glass coated on both sides with 6 x 8 in. sheets of tin foil with lugs projecting alternately first on one side and then on the other as the units are assembled. The construction of this type of condenser is thoroughly covered in other chapters of the book. The Vacuum Tube Oscillation Transformer.-This oscillation transformer is of the Oudin type comprising a secondary of 200 turns of No. 18 annunciator wire in a single layer wound upon a cardboard cylinder 8 in. in diameter and 13 in. long, and a primary helix of 10 turns of edgewise wound copper strip having an inside diameter of 10¾ in. The primary turns are supported by rectangular pillars of fibre or hard rubber preferably mounted upon an independent base in order that the complete transformer may be removed from the table without difficulty. The top turn of the secondary winding is connected with the brass ball surmounting the coil while the bottom turn is connected with a common ground terminal which is mounted upon a copper bar running the entire length of the table. The bottom turn of the primary helix is likewise connected with this ground terminal. The X-Ray Oscillation Transformer.-This coil is of the oil-immersed type. Fig. 7 shows clearly the method of construction and the reader will note that the transformer is a combination of the Tesla and Oudin types. Two secondary coils are wound upon 6 x 8 in. cylinders of cardboard and the winding is to be of No. 22 D.C.C. wire wound in a single layer until 200 turns are in place on each of the cylinders. The turns are either to be spaced in a lathe or else wound with a coarse thread between, for it is essential that they be separated fully the thickness of a piece of the wire in order that the very high potential between turns may not puncture the insulation. Both secondary coils are,