serves to insulate the other tube elements. As in the case of the disc seal, it can be made either with the edge of a metal not in contact 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 welded 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.
