Chapter XIV: Effects of manufacturing deviations on crystal units for filters

TLDR: The first telephone use of crystal units in the commercial manufacture of filters was made by the Western Electric Company in about 1936 as discussed by the authors, and the quantitative data collected for this purpose provided the chief source of material for this chapter.

Abstract: THIS chapter emphasizes primarily the need for close control in the manufacture of crystal units for use in filters. The first telephone use of crystal units in the commercial manufacture of filters was made by the Western Electric Company in about 1936. To make such commercial manufacture practical, it was necessary to establish accurate design information and allowable manufacturing tolerances. The quantitative data collected for this purpose provided the chief source of material for this chapter. While the data is quite extensive, it will be observed that there are still some factors which must be treated qualitatively.