ELECTRON TUBES FOR A TRANSATLANTIC TELEPHONE CABLE 187 



Second, all tubes were subject to intensive visual scrutiny in which 

 some 80 specific constructional details were checked for possible faulty 

 assembly. 



Third, the Ufe characteristics of transconductance, total emission and 

 working point were examined over the test period of about 4,000 hours 

 for unsatisfactory trends. Although this type of specification is more 

 difficult to define precisely, its application is probably more rigorous and 

 exacting than any of the previous specifications. 



Only if a tube passed the conventional test and the three supple- 

 mentary tests was it considered adequate for inclusion in a repeater. 



Fig. 1-1 — View of interior of a 6P12 type tube. 



