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IX. Xote on the Effects of Grid Currents in Three- Electrode 

 Ionic Tubes. By E. V.' Appleton, M.A., B.Sc, St. Johns 

 College, Cambridge *. 



IN the interpretation of the functioning of three-electrode 

 ionic tubes, which are now used so extensively in the 

 reception of wireless signals, we have to consider simultaneous 

 effects in two electrical circuits, which may be defined as 

 follows : — 



(a) The grid or input circuit, which is completed inside 



the tube by the space between the incandescent 

 filament and the perforated grid, and 



(b) the plate or output circuit, which is completed inside 



the tube by the space between the filament and the 

 metal plate. 



The variables to be considered are thus as follows : — 

 Plate current, plate voltage, grid current, grid voltage, and 

 filament temperature, the values of which maybe represented 

 by the letters I, V, i, v, and 6 respectively. The complete 

 working of the tube can only be interpreted when the static 

 characteristic surfaces representing the relations between 

 any three of the above quantities are known. In the case of 

 a tube acting as a relay or amplifier, the main surface to be 

 considered is that represented by the equation /(I, V, v) = 0. 

 Vallaurif has shown how this may be expressed approxi- 

 mately as I = av4 6V + C, where a, b 7 and c are constants, and 

 has applied it to the elucidation of many wireless circuits. 

 Hazeltine t lias recently made substantial additions to that 

 part of Vallauri's w T ork dealing with oscillating audion 

 circuits. In both cases the effects of the currents flowing in 

 the grid circuit were neglected. 



The magnitude of the grid currents involved is known if 

 we know the contour of the (i, v, V) surface. In general, 

 this surface cannot be represented by a simple expression, 

 but for small changes of the quantities concerned we may 

 write 



Ai = K 1 &v + K 2 &V, (1) 



where k x is the slope of the (v, i) Y=Y(t curve and k 2 is the 

 slope of the (V, i) v=v curve. 



The quantity atj may be either positive or zero in a tube of 



* Communicated by the Author. 

 t G. Vallauri, L ' Elettrotecnica, iv. 3, p. 43 (1917). 

 X L. A. Hazeltine, Proc. Inst. Bad. Eng., April 1918. 

 Phil. Mag. S. 6. Vol. 37. No. 217. Jan. 1919. K 



