ELECTRON TUBES FOR A TRANSATLANTIC TELEPHONE CABLE 175 



celerated aging tests which showed it to be superior to melts 60 and 

 G3 from an interface standpoint. 



The interface problem will be discussed further in a later section. 



As the development of the tube proceeded, both the processing of the 

 parts and the cleanliness of the mount assembly were impro\'ed and the 

 cathode emission level increased. Life tests indicated that better therm- 

 ionic life might be obtained by operating at a lower cathode tempera- 

 ture. Accordingly a cathode power of approximately 4.0 watts was 

 adopted, which corresponds to a temperature of 670°C. A life test, now 

 45,000 hours or about 5 years old, shows the results in Fig. 8 of operating 

 groups of tubes at three different cathode temperatures. This is a well 

 controlled test in that the tubes for the three groups were picked from 

 tubes having common parts and identical fabrication histories. It may 

 be noted that the average of the 725°C lot has lost approximately 5 per 

 cent of the initial transconductance, whereas the 4.0 watt group after 

 about 5 years has lost essentially none of its transconductance. The 3.0 



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CATHODE TEMPERATURE =670° C 



10,000 20,000 30,000 40,000 50,000 



LIFE IN HOURS AND YEARS 



Fig. 8 — Results of operating thirty-six 175HQ tubes divided equally among 

 three different cathode temperature conditions. For each of the curves the cathode 

 core material used was half from melt 60 and half from melt 63. The conditions 

 in cable operation are essentially those represented by the center curve. 



