ELECTRON TUBES FOR A TRANSATLANTIC TELEPHONE CABLE 173 



LU 



o 



z 



LU 



cr 



UJ 



u. 



105 



100 



z 



LU 



u 



LU 



^95 

 < 



5 90 

 Q 



Z 



(J 85 

 ^80 



75 

 70 



20,000 



40,000 



60,000 



80,000 



100,000 120,000 



LIFE IN HOURS AND YEARS 



Fig. 6 — Results of life tests on eighteen 175HQ tubes operating at two differ- 

 ent current densities. 



The cathode temperature is one of the most critical operating vari- 

 ables affecting thermionic life. As mentioned above, the early develop- 

 ment objective was a cathode power of 5.0 watts which corresponded 

 to 710°C for the cathode design used at that time. The results of op- 

 erating at this condition are illustrated in Fig. 7. No tubes have been 

 lost from the test where the direct cause has been failure of emission. 

 Several tubes were lost because of mechanical failure resulting from 

 design defects which were subsequently corrected. It will be observed 



120 

 110 

 100 

 90 

 80 

 70 

 60 

 50 

 40 



20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 



LIFE IN HOURS AND YEARS 



Fig. 7 — Results of life tests on sixteen 175HQ tubes operating at a cathode 

 temperature of 710°C. 



