stage Amplifiers 



195 



A METHOD OF MEASURING THE AMPLIFICATION OF 

 TWO OR MORE STAGE AMPLIFIERS. 



R. R. Ramsey, Indiana University. 



The method here explained is an adaptation of the potentiometer 

 method of measuring the amplification constant of an electron tube. 



In figure 1 (Audio Amplifier) the negative terminal of the filament 

 is connected to the middle point, b, of a potentiometer made of two ordi- 

 nary resistance boxes. This negative terminal may be connected to the 

 earth also. An alternating E.M.F., generated by a buzzer working- 

 through a telephone induction coil, is connected to the terminals, c, c, 



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of the potentiometer. The point, a, is connected to the grid of the first 

 tube and the point, c, is connected through a suitable B battery and 

 telephone to the plate of the last tube. 



The tubes are carefully connected with audio frequency coils. The 

 coil must be so connected that when the potential of the grid of tube 

 No. 1 is made positive the potential of the second and of all other tubes 

 is positive. When the grid potential of the first tube is made positive 

 the plate current of all tubes must increase. A second B battery must 

 be used for the plate potential of all tubes except the last. 



When the potential of the point a is positive the current runs from 

 a to c through b. The potential of c will be negative, since the potential 

 of b is zero. 



If the potential of the grid of tube No. 1 is raised, the current 

 in the plate circuit of the last tube is increased unless the plate poten- 

 tial is decreased. When the plate potential is diminished enough to 

 keep the plate current constant there will be a minimum sound or no 

 sound at all in the telephone. 



"Proc. 38th Meeting, 1922 (1923)." 



