ARMSTRONG, OPERATING FEATURES OP THE AUDION 



221 



effect of high-frequency oscillations in the grid circuit on the wing cur- 

 rent will be reversed. The amplitude of the negative part of the high- 

 frequency oscillations in the wing circuit will exceed the amplitude of 

 the positive part and the condenser C\ will become charged, but in the 

 opposite sense, the side connected to the battery Bo becoming negative. 

 The discharge of the condenser through the telephones will therefore be 

 in the opposite direction to the flow of the continuous current of the wing 

 circuit, and will constitute a decrease in the telephone current. Dia- 

 grammatically the action is as indicated in Fig. 9. 



Oscillograms bearing on these actions were obtained in the matter indi- 

 cated in Fig. 10. Oscillations were set up by the discharge of the con- 

 denser r" through the inductance U, which was coupled with the in- 



FiG. 13 



ductance L of the tuned grid circuit. To permit the use of an ordinary 

 General Electric oscillograph, an oscillation frequency of about fifty 

 cycles per second and a group frequency of two or three cycles were em- 

 ploj^ed. The action of the audion is the same, regardless of frequency, 

 provided that the circuit constants are suitably modified to fit the fre- 

 quency employed. In this ease the oscillation frequency of the circuit 

 C'jC' was fifty cycles and the circuit LC was accordingly tuned to the 

 same frequency. The capacity of C^ was selected to correspond to the 

 'low frequency employed. Figs. 11 and 12 show oscillograms taken as 

 indicated in Fig. 10, with the grid potential adjusted respectively to the 

 lower and the upper bends of the operating characteristic. It will be 

 observed that the telephone current reaches in Fig. 11 its maximum 

 value, and in Fig. 12 its minimum value, when the oscillating current 

 has almost died away. This effect would be shown more plainly with a 

 higher oscillation frequency, but even at the frequency used it is quite 

 evident. 



