ELECTROX TUBES FOR A TRANSATLANTIC TELEPHONE CABLE 177 



mately 28 tubes made. The data were taken after 5,000 hours of aging. 

 A sharp improvement in thermionic emission was noted at a point on the 

 chart where about one half of tubes had been fabricated. An examination 

 of the records, which are very carefully maintained, disclosed that the 

 windows of the assembly room were sealed and air cleaning and condi- 

 tioning was put in effect at the point indicated on the chart. No other 

 changes in processing or materials occurred at this time. A second definite 

 improvement in thermionic emission occurred when the work was moved 

 from the location in New York City to the new and better controlled 

 environment at Murray Hill in New Jersey. 



Fabrication and Selection 



All assembly operators on the 175HQ tube program wore nylon* 

 smocks to keep down the amount of dust and lint that might otherwise 

 leave their clothing and get into the tubes. Rayon acetate gloves were 

 worn when handling parts as a protection against perspiration. Rubber 

 finger cots did not prove satisfactory because they covered too little area 

 and once contaminated they did not absorb the contaminant. 



The tubes for the Newfoundland to Scotland section of the cable were 

 made at Bell Telephone Laboratories under the extremely close engineer- 

 ing supervision of many of the original development engineers. All ma- 

 terials going into the tubes were carefully checked, and wherever possible 

 they were tried out in tubes. Experience under accelerated aging condi- 

 tions was obtained before these materials were used. For example, al- 

 though during the development period all glass bulbs were used as re- 

 ceived without any failures resulting, less than one-cjuarter of the bulbs 

 bought for the actual cable job passed the inspection requirements. Each 

 batch of heaters was sampled and results obtained on intermittent and 

 accelerated tests before approval for use. 



The fabrication of the tube was carried out with extreme care by op- 

 erators especially selected for the job. If normal commercial test limits 

 were applied to the tubes after exhaust, the yield from acceptable mounts 

 would have been about 98 to 99 per cent. Yet only approximately one 

 out of every seven tubes pumped was finally approved for cable use. 

 All tubes were given 5,000 hours aging and electrical tests were made at 

 six different times during this period. The results weighed heavily in 

 the final selection. For example, a correlation between thermionic 

 life and gas current had been established during the tube develop- 



Trade name for DuPont polymide fibre. 



