RADIO COMMUNICATION 263 



Before the tube is mounted on the base, the detector should 

 be procured or made, and provision made for the phone terminals 

 at one end of the base, and for the binding-post for the ground 

 connection on the other end of base (Fig. 119). 



It is suggested that a crystal detector be purchased. This 

 detector may be of the type that can be adjusted or one that is 

 always in adjustment. If it is desired that the detector be 

 made, it would be well to investigate various devices on the 

 market and duplicate one of the numerous types. Essentially 

 the detector merely consists of a small crystal of selected galena 

 or iron pyrites, which is touched with light pressure by a small 

 spring wire known as a "cat whisker." One connection is made 

 to the whisker and the other to the crystal. The crystal may be 

 imbedded in fusible alloy, and secured to the base board with 

 screws. A binding-post may be set in the base close to the crystal, 

 and the whisker secured to the binding-post in such a manner 

 that it loops over with its point resting lightly on the surface of 

 the crystal. 



A small radio-phone condenser should be purchased and 

 mounted at one end of the base between two binding-posts 

 provided with holes to take the terminals of the cord leading to 

 the phones. The spacing of these binding-posts is determined 

 by the phone condenser, which is a small strip with holes in each 

 end for the binding-posts. 



The set is now ready to be mounted on the base board and 

 connected up. As small holes are to be drilled in the base board 

 for the connecting wires, it is advisable to assemble the set first 

 in order to determine the position of these holes before securing 

 the parts permanently. 



The tuning coil is mounted at one end of the base with the end 

 piece one inch from the end of the base and one-half inch from 

 each edge of the base. Wire finishing nails may be used to secure 

 the end pieces of the coil to the base board. The tube with its 

 layer of wire is glued into the grooves with the ends of the winding 

 down. These ends are threaded through holes previously drilled 



