FLEXIBLE REPEATER MANUFACTURE 135 



was checked and units were then assembled into cans and ceramic covers 

 soldered in place. Assemblies were pressurized with air, through a hole 

 provided for the purpose, while the assembly was immersed in hot water 

 to determine if leaks were present. Capacitors were then baked, vacuum 

 dried, impregnated, pressurized with nitrogen, and sealed off. The com- 

 pletely sealed units were then placed in a vacuum chamber at a tem- 

 perature of 150° F, 2 mm. mercury, for 3 hours to check for oil leaks. 

 Capacitance was rechecked and insulation resistance measured. 



After seven days, capacitors were unsealed to replenish the nitrogen 

 that had been absorbed by the oil, resealed and again vacuum leak tested. 

 An X-ray examination was then made of each individual unit to verify 

 internal mechanical conditions. Capacitors were then placed in a tem- 

 perature chamber and given the following treatment for one cycle : 



16 hours at 150°F; 8 hours at 75°F; 16 hours at 0°F; 8 hours at 75°F. 



At the end of ten days, or 5 cycles, the insulation resistance and con- 

 ductance was measured and a norm established for capacitance. 



Capacitors were then recycled for ten days, and, if the capacitance 

 had not changed more than 0.1 per cent, they were satisfactory to place 

 on production life test. If the foregoing conditions had not been met, 

 the capacitors were recycled for periods of ten days until stabilized. 



At that time, 10 per cent of the capacitors in every production lot 

 were placed on "Sampling Life Test", which consisted of applying 4,000- 

 volt dc in a temperature of 150°F for 25 days. At the same time, the 

 balance of the capacitors in the lot were placed on production life test 

 at 3,000-volt dc in a temperature of 42°F for 26 weeks. At the end of 

 this time, the insulation resistance was measured and the capacitance 

 checked at 75°F and at 39°F. The difference in capacitance at the two 

 temperatures could not exceed -|-0.001, —0.005 mf, and the total ca- 

 pacitance could not exceed maximum 0.3726, minimum 0.3674 mf. The 

 capacitance from start to finish of the life test could not have changed 

 more than plus or minus 0.1 per cent. 



If all of the preceding requirements had been satisfied, the particular 

 lot of capacitors described was considered satisfactory for use. 



The foregoing examples are typical of the procedures evolved for 

 insuring, to the greatest degree possible, the long, trouble-free life of all 

 apparatus used in the repeater. 



Radioisotope Test 



There were many new and involved tests which were developed and 

 applied to the manufacture of repeaters. One of the most unique is the 

 use of a radioisotope for the detection of leaks under hydraulic pressure. 



