FLEXIBLE REPEATER MANUFACTURE 121 



fections visible under SOX magnification were permitted. This resulted 

 in a process shrinkage five times that experienced in normal crystal plate 

 manufacture. 



In this use, the crystal units were required to meet performance tests 

 at currents as low as one-thousandth of a microampere — far below the 

 current values usually encountered. Improved soldering techniques had 

 to be developed for soldering the gold plated phosphor bronze and nickel 

 wires used, because it was found that the electrical performance of the 

 units was directly related to the quality of soldered connections. 



Although one-seventh of Western's production of quartz crystal units 

 are in glass enclosures, the applicable techniques in glass working re- 

 quired a complete revision. Glass components such as the stem and bulb 

 purchased from established sources were found to be far below the stand- 

 ard required for this crystal unit. For example, the supplier of the glass 

 tubing used in the manufacture of stems was reciuired to meet raw mate- 

 rial specifications that embodied coefficient of thermal expansion, soften- 

 ing point of glass, density, refractive index, and volume resistivity. The 

 glass stems made from this tubing by regular manufacturers were found 

 unacceptable and the processes used by these sources could not be readily 

 adapted to meet the desired specifications. The glass stems contained 

 four lead wires made from 30-mil Grade "A" nickel wire butt welded to 

 16-mil light borated Dumet wdre. To assure the quality of the metal to 

 glass seal, each wire was inspected under 30X magnification for tool 

 marks and other surface imperfections. The finished stem assemblies 

 were inspected under SOX magnification for dimensions, workmanship, 

 cleanliness and minute glass imperfections, then individually stored in a 

 sealed plastic envelope. 



The glass bulb in this crystal unit is known as the T921 design com- 

 monly used in the electron tube industry. The high quality required, 

 however, made 100 per cent inspection necessary. Examination under 

 SOX magnification resulted in rejected bulbs for presence of scratches, 

 open bubbles, chips and stones. Physical limits for inside and outside 

 diameters as well as wall thickness were causes for additional rejects. 

 Only one per cent of the commercial bulbs were found acceptable, and 

 these were also stored in a sealed plastic envelope. 



The final major assembly operation consisted of sealing the glass bulb 

 to the stem which had had the crystal sub-assembly welded to the nickel 

 wires. The techniques for "sealing in" used in quartz crystal or electron 

 tube manufacture were unsuited. Two important factors in this crystal 

 unit, which required the development of new processes, were the prox- 

 imity of soft soldered connections to the sealing fires and the demands 



