340 BELL SYSTEM TECHNICAL JOURNAL 



The principal operational problems encountered in the 3J21 magnetron 

 were the occurrence of so-called "gassy tubes" and some difficulties with 

 "moding." Despite numerous precautions taken during fabrication, gas, 

 identified spectroscopically as hydrogen, was evolved during operation 

 in a discouragingly large number of magnetrons during the developmental 

 work. By the use of a zirconium getter attached to the cathode support 

 cone the difficulty could be circumvented. Also it had been found possible 



Table IV 

 The 3J21 Packaged Magnetron at 1.25 Centimeters 



N 18 



re (in.) 0.048 



ra (in.) 0.080 



A (in.) 0.186 



Magnet gap (in.) . 290 



Weight (lb.) 6.6 



Resonator system "rising sun" 



Resonators vane type 



Resonator X ratio 1-8 



X(cm.) 1.25 



/ (mc/s) 23986 ± 240 



Nearest modes m = 4, w — 8 



X separation (%) +25, - 10 



Qo 1400 



Oext 580 



nc (%) 70 



Output circuit wave guide with X/2 



stabilizing cavity 

 Stabilization factor 2 



V (kv.) 15.0 15.0 



/(amps.) 15 15 



B (gauss) 8000 8000 



t(A) 0.5 0.25 



pps 1000 2000 



A(kw.) 60 60 



r,{%) 26 26 



r,A%) 37 37 



PF (mc/s) 17 17 



to "clean up" a gassy tube temporarily by running the cathode very hot. 

 This led to a pumping cycle which greatly reduced the occurrence of hy- 

 drogen. 



Considerable effort was expended in attempting to track down the source 

 of the hydrogen evolution. The iron pole pieces were found to be the 

 major offender, but some hydrogen was evolved from other parts including 

 the cathode. Cleaning and plating solutions release atomic hydrogen 

 which readily permeates the iron pole pieces and other parts. Various 



