290 BELL SYSTEM TECHNICAL JOURNAL 



In commercial practice a single operator runs three units simul- 

 taneously and produces about 90 broadcasting microphone diaphragms 

 a day. These diaphragms require a gold spot on both sides which 

 necessitates breaking the vacuum and turning the parts over. The 

 time not occupied in loading the fixtures and operating the equipment 

 is taken up in preparing diaphragms for sputtering, marking, and 

 packing the finished product. It requires about forty minutes to de- 

 posit from three to five mg. of gold per spot. Although this deposit 

 is not more than .001 mm. thick, it is very continuous, adherent, and 

 altogether suitable as a microphonic electrode surface (Fig. 6). 







Fig. 6 — Typical magnified gold surfaces after three months' service. The spot on the 



left was produced by electrolytic plating and shows many blisters; the 



one on the right was produced by sputtering. 



This equipment has been in successful operation for a number of 

 years in the production of microphone diaphragms. 



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