504 BELL SYSTEM TECHNICAL JOURNAL 



The cathode, spacer, and grid comprising the cathode-grid subassembly 

 are riveted together under several pounds of force maintained by the 

 molybdenum spring on the bottom of the assembly. The rivets are three 

 synthetic sapphire rods fired on the ends with matching glass. In Fig. 4, 

 the parts comprising this assembly are shown in appropriate pile-up se- 

 quence at the left, and the completed cathode-grid subassembly is shown 

 at the right between the bulb and the press. The grid-anode spacing of 

 .012" is easily obtained by means of an adjustable anode plug the sur- 

 face of which is gauged relative to the bulb grid disc. 



Fig. 5. — Spectrum formed by the grid of the 1553 microwave triode. 



Table I 

 Low-Frequency Characteristics 



For Vp = 250 V, Ip = 25 ma, Vg = -0.3 V 



g„ = 50,000 MHihos 

 M = 350 

 r„ = 7000 ohms 



Ckg = 10 finf 



Cgp = 1 . 05 ^l^if 

 Ckp = .005 nnf 



The higher current density of 180 milliamperes per square centimeter, 

 the thin dense cathode coating, and the very close spacings, posed a 

 problem in obtaining adequate emission and freedom from particle 

 shorts, and had to be solved by quality control methods because of the 

 large number of factors involved and the precision required. Tubes, sub- 

 assemblies, and testers have been made in batches and studied by statis- 

 tical methods. To achieve a state of statistical control on emission, and 

 freedom from dust particles, it is necessary to process the parts and 

 assemble the tubes in a rigorously controlled environment. Completely air- 

 conditioned processing and assembly rooms operating under rigorous con- 

 trols have been found necessary^ Under such controlled conditions, good 

 production yields with satisfactory cathode activity have been obtained, 



•R. L. Vance, Bell Laboratories Record, 27, 205-209 (June 1949). 



