A HIGH POWER VACUUM TUBE 



11 



serves to insulate the other tube elements. As in the case of the 

 disc seal, it can be made either with the edge of the metal not in con- 

 tact with the glass, as shown at A, or with the metal sharpened to a 

 fine edge which is in contact with the glass. The glass may be 

 situated either inside or outside of the metal, see B and C. 



The first thermionic tubes in which these seals were embodied were 

 made of. copper and were designed to operate at 10,000 volts and to 

 give about 5 k. w. output. 



A photograph of one of these tubes is shown in Fig. 6; and the 

 filament grid assembly is shown in Fig. 7. 



Fig. 6 



Fig. 7 



The anode consists of a copper tube 1.5'' in diameter and 7.5 long. 

 A copper disc is wielded to one end forming a vacuum-tight joint. 

 The other end which is turned down to a knife edge is fused directly 

 to a glass tube. 



