FLUCTUATION NOISE IN VACUUM TUBES 



647 



The conditions found most suitable for quiet operation of the No. 

 102G tube and the corresponding average tube characteristics are 

 given in the first two columns of Table I. Under these conditions the 



TABLE I 



Wfstern Electric No. 102G Tube 



average equivalent tube noise voltage, referred to the grid circuit, is 

 given in the last column of the same table. These noise data are given 

 in terms of Rg, the experimentally determined equivalent noise re- 

 sistance of the tube, and in terms of Vf^, calculated by means of 

 equation (14), for each of the four frequency ranges shown in Fig. 4. 



The No. 102G has the lowest noise of all the tubes tested and was 

 found suitable for use in the first stage of high-gain amplifiers where 

 tube noise is the limiting factor, provided it is not required that the 

 input capacitance and microphonic response to mechanical and 

 acoustical shock be extremely low. 



No. 264B Tube 



This is a three-element filament-type tube. Due to the rigid con- 

 struction and the short filament which is designed to reduce vibration 

 to a minimum, the microphonic response of the tube to mechanical 

 and acoustical shock is exceptionally low.^* The extensive system of 

 spring suspensions and the heavy sound-proof chamber usually re- 

 quired for shielding low noise tubes may be simplified when using the 

 No. 264B. In addition, this tube has good temperature saturation, 

 low power consumption, and high stability of operation. 



The operating conditions and noise data for this tube are given in 

 Table II. Although the noise of this tube is slightly higher than that 



15 M. J. Kelly, 5. M. P. E. Jour., 18, 761 (1932). 



