ELECTRON TUBES FOR A TRANSATLANTIC TELEPHONE CABLE 183 



6.6 

 6.5 



6.4 

 6.3 

 6.2 

 6.1 

 6.0 

 5.9 



Ljj 5.8 

 U 



Z 



1^5.7 

 (J 



O 



o 



1 5.5 

 ir 



5.4 



5.3 



5.2 



5000 10,000 15,000 20,000 



LIFE IN HOURS AND YEARS 



25,000 30,000 



Fig. 10 — Behaviour of a group of 50 tubes deliberately left with a "gas gen- 

 erator" (tube type 6P12). 



free to recover from transconductance failure when the gas attack has 

 passed. In Fig. 10 is shown the behaviour of a group of 50 tubes which 

 have been deliberately left in possession of a component capable of gen- 

 erating carbon-monoxide over a prolonged period of time. The curve 

 shows the characteristic recovery of a platinum-cored oxide-cathode with 

 the gradual passing of what is thought to be a typical gas attack. 



One problem that has attracted much attention at Dollis Hill is the 

 actual manner in which a platinum-cored cathode recovers from a gas 

 attack. The mechanism must involve the dissociation of a small fraction 

 of the oxide cathode itself with the retention of barium metal in the 

 oxide lattice and the evolution of oxygen. That such an essential mecha- 

 nism does in fact exist has been proved by the slow accumulation of barium 

 metal in the platinum core. This accumulation takes the form of a dis- 

 tinctive alloy of barium and platinum and only occurs when the cathode 



