MICROPHONIC NOISE IN VACUUM TUBES 633 



ress has been made in recent years in effecting an adequate reduction 

 of leaks economically, and in applications where requirements for 

 exceptionally low noise levels warrant slightly increased manufacturing 

 costs, almost any degree of reduction of leaks may be obtained. 



Conclusion 



The methods which have been outlined for reducing microphonic 

 noise by cushioning and by making use of the quiet tubes which are 

 available are, for the present, adequate to meet all but the most ex- 

 treme requirements. Should the necessity for further reduction be- 

 come sufficiently urgent in the future, however, it can probably be ob- 

 tained either by designing still quieter tubes or by improving the cush- 

 ioning of sockets. The latter course appears to be the more economical. 

 In either case, however, greatest effectiveness can be attained by con- 

 sidering particular types of tubes and sockets in their relation to one 

 another. 



The author is greatly indebted to Drs. M. J. Kelly and H. A. Pidgeon 

 for their kind cooperation and many helpful suggestions in the course of 

 this work. 



