1118 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



418A tube. The L3 frame grids are illustrated in Fig. 12, together with a 

 conventional control grid from the 6AK5 tube and the control grid from 

 the 404A vacuum tube. The conventional grid consists of two large side 

 rods, usually of nickel, around which is spirally wound the grid lateral wire. 

 The lateral wire is joined to the side rod at each intersecting point by first 

 knifing a groove into the side rod, laying the lateral wire into the groove, 



GETTER 



CATHODE 



-• PT--MICA DISK 



PLATE 



-FRAME GRID 



■rh MICA DISK 



Fig. 11 — Cutaway view of the 437A. 



and then swaging the groove closed. Since, in these conventional grids, the 

 lateral wire is usually larger than 0.0008" diameter, the grid is self support- 

 ing and needs no strengthening members. For the high figure of merit tubes, 

 control grid lateral wires of the order of 0.0003" diameter are needed. Wire 

 of this diameter is not self supporting in the necessary lengths and for that 

 reason the two large side rods are first joined together by the cross straps 



