THE L3 SYSTEM — QUALITY CONTROL IN MANUFACTURE 995 



and the lateral is placed in this groove. The groove is closed by swaging 

 to fix the lateral in place. In the L3 tubes, the grid lateral wire is ap- 

 proximately 0.0003" in diameter and the grid to cathode spacing is 

 approximately 0.002". A ten per cent change in grid cathode spacing 

 would result in a change in transconductance of fourteen per cent. It is 

 important, therefore, that the control grid be maintained very accurately 

 to insure proper grid to cathode spacing. A conventional grid made with 

 such small diameter lateral wire would not be self-supporting in the length 

 of span required and could not be made with the accurate control of 

 diameter needed. Since the size of lateral wire used and the close spacing 

 of adjacent turns preclude notching and swaging, some other method of 

 holding the laterals in place must be employed. Accordingly, a new type 

 of grid construction is used. This consists of making a supporting frame 

 from two large side rods joined together by cross straps located at the 

 ends of the grid proper. On this rigid frame the fine lateral wires are 

 wound. This frame type of grid was described in previous articles.^' ^ 

 In the L3 grids, the lateral wires have been bonded to the support rods 

 by a glass suspension sprayed along the edge of the support rods. This 

 glass glaze is sintered at a temperature of approximately 700°C to hold 

 the laterals firmly in place. The earlier design used a gold brazing opera- 

 tion to secure the laterals. This brazing was done at a temperature of 

 approximately 1070° C. The newer method at the lower temperature 

 produces less stretching of the laterals and as a result higher residual 

 tension is obtained. This is a distinct advantage in reducing noise and 

 the possibility of grid to cathode shorts. 



With the new method of holding the laterals in place, the grids are 

 gold plated after the glazing operation is completed. Gold plating is 

 necessary in order to minimize thermionic emission from the grid wires 

 due to the closeness of the grid to the hot cathode and the possibility 

 that active cathode coating material may be deposited on the grid during 

 processing and operation. 



3.62 Distribution Requirements 



Distribution requirements haved been place on transconductance as 

 well as the most critical inter-electrode capacitances, the input capaci- 

 tance, Cg.^kg, , for the 435A and 436A tubes and the grid to plate capaci- 

 tance, Cg-p , for the 437A. In the case of the 435A and 437A tubes, control 

 of modulation is also required. Since transconductance is of primary 

 importance, this characteristic has been selected as the one which 

 governs shipment of product. Inter-electrode capacitance and modula- 



