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BELL SYSTEM TECHNICAL JOURNAL 



TABLE II 

 Western Electric No. 264B Tube 



of the No. 102G, the lower microphonic response and the lower power 

 consumption make it a more desirable tube to use in input stages of 

 certain high gain amplifiers. 



No. 262A Tube 



This is a three-element tube having an indirectly heated cathode. 

 It is designed to give a microphonic response to mechanical and 

 acoustical shock ^^ still lower than that of the 264B. Except for 

 frequencies below 200 cycles per second it was found that no acoustic 

 shield was necessary for this tube even when working at extremely low 

 levels. Although this tube is designed to have a low hum disturbance 

 resulting from alternating current for heating the cathode (the inter- 

 ference from this effect can be held to less than 7 X 10~^ equivalent 

 input volt), direct current power was used in the measurements here 

 described. 



The operating conditions and noise data for the No. 262A tube are 

 given in Table III. 



No. 259B Tube 



This is a four-element, screen-grid tube having an indirectly heated 

 cathode. Its comparatively high amplification factor makes possible 

 a relatively large gain per stage so that when it is used in the first 

 stage of a high-gain amplifier succeeding stages contribute nothing to 

 the total noise. 



Noise measurements on the No. 259B tube show that the signal-to- 

 noise ratio is approximately independent of the plate voltage over a 



