990 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



■CELLS- 



LOWER MIDDLE UPPER 



UNIT CAPACITANCE 



Fig. 10 — A summarized frequency distribution of a 310.5-mmf mica condenser 

 at various stages of manufacture. 



3.32 Quartz Disc Capacitors 



The quartz disc capacitors are made by the addition of a silver coating 

 to fused quartz discs which have been lapped to an exact thickness. The 

 final adjustment for capacitance is obtained by the mechanical removal 

 of small areas of the silver before the application of a protective finish. 

 The nature of the manufacturing process and the quantities produced 

 requires the three-cell method. A typical requirement is 9.8 ±0.1 mmf 

 which requires the measurement and classification of the product into 

 cell widths of 0.067 mmf each. Capacitance measurements, including the 

 use of reference standards, combined with careful adjusting procedures, 

 have resulted in shipping approximately 99 per cent of the capacitors 

 produced. 



3.4 BORO-CARBON RESISTORS 



3.41 Introduction 



The stringent requirements for L3 carrier line amplifiers and imped- 

 ance matching and balancing networks prevented the use of commer- 



