ELECTRON TUBES FOR A TRANSATLANTIC TELEPHONE CABLE 165 



the continuity of service depend on two essentially independent strings 

 of tubes has been carried over to the repeater design for the Clarenville- 

 Sidney Mines section of the transatlantic cable. 



In the Post Office system containing 84 tubes in the submerbed re- 

 peaters, five tube failures randomly occurring in the system will result 

 in slightly over fifty per cent probabilitj^ of a system failure; one tube 

 failure in the 306 tubes in the Newfoundland-Scotland section of the 

 system will result in certain system failure. It is not surprising, therefore, 

 to find the tube designed for the Newfoundland-Scotland section of the 

 cable to have extremely liberal spacing between tube elements in order 

 to minimize the hazards of electrical shorts. This results in a lower trans- 

 conductance than is found in the tubes designed for the Nova Scotia- 

 Newfoundland link. Other factors in the design will be recognized as 

 reflecting the different operating hazards involved. 



Early models of the British Post Office and Bell Laboratories tubes, 

 together with the final tubes used in the cable system, are shown in 

 Fig. 1. 



mmmm 



ifc 



Fig. 1 — The final designs of tubes for the Nova Scotia-Newfoundland section 

 of the cable (right) and for the Newfoundland-Scotland section (left). Earlv 

 models of each type stand behind the final models. 



