///(;// rREQuriiVcy ami'liiieks 



ia3 



At lii^liiT lRM|iii'nrics suflirii-iiil\- liigh inipcdanrfs ran otiK- he 

 obtaiiu'tl by workiiij; at the natural frccimniry of llu" iransforniiT, and 

 to illustrate this we shall in the followini; i;i\e some results of experi- 

 ments made with ordinary tuned circuit aniplitiers, choke coil ampli- 

 fiers and loosely coupled transformer amplifiers at high frequencies. 



Tl'NED riR(l IT ANT) ClIOKI'; ("(HI. .XmI'MI" IKRS 



In E'it;. 2 there are shown to the left two dilTereiit wa\s of conned iiig 

 up a tuned circuit amplilier, and to the right are gi\cn the corre- 

 sptinding etiuivalent circuits. The injiut imjiedance to the next 

 tube is assumed to be a pure resistance Rg. thus neglecting the grid- 



TUBE CIRCUIT 



r 



Pr^¥T^r^ 



cJo^L 



R=R,+R2* R^. I- = L, + L2i-2M, 



EQUIVALENT CIRCUIT 



^9 lui- >'l'"-2 U.-U Co' C ' R ' 



ojo = 2 1tjo, Jo~^^5onani: frequency 



Fig. 2 — Schcm.Ttic of Tuned .Amplifier Circuits 



filament capacity and the grid-plate capacity of this tube. The 

 effect of the grid-filament capacity, however, will only be to detune 

 the circuit a little and can, therefore, he compensated for by retuning 

 the condenser C (or Ci and C;) and the effects of the coupling through 

 the grid-plate capacity of the second tube will be treated specially 

 later. 



Fig. 2 gives the well-known formulas for the equivalent series re- 

 sistance R' of the circuit at resonance and for the impedance of the 

 circuit Za-h measured between points a and b at resonance. 



