THERMIONIC VACUUM TUBES 



47 



(about 10X10" 12 farads) but is approximately 120X10 12 farads. 

 Fig. 16 shows that the effective conductance is also greatly increased 

 above that clue to r x . This increase in conductance means an in- 

 creased absorption of input energy by the tube which, of course, is 



■ jnce r;ir»0htri5. 



Fig. 16 



i 

 l 



I 



Output Re** 



Fig. 17 



not dissipated in the grid circuit but passes through the path supplied 

 by the condenser C 3 to be wasted in the plate circuit. 



In case Z 2 is a pure inductance L 2) the effective input conductance 

 of the tube is negative and not positive as in the preceding case. 



?0000 30000 JO0O0 50000 



teadaice LjmOtnu 



: r:-;c 



.:;■:■: roooo 



Fig. 18 



Fig. 19 



Fig. 18 shows the variation of this negative conductance with L 2 , and 

 Fig. 19 the variation of effective input capacity with L 2 . A negative 

 input conductance means that the grid circuit draws power from the 

 plate circuit; if the negative conductance is large enough, a tuba in 



