mail VREQVEXCY .IMl'l.niliKS 



199 



As an illustration of the I'lTect i)f this "feed back" action, tiu-re are 

 Riven in Kig. 12 some curves obtained for a two-stage high freqiienc\- 

 antplitier with loosely coupled transformer stages. The input circuit 

 to the amplilier consisted of a loop antenna circuit tuned to the fre- 

 quency of the induced signal. 



Curve .4 shows the straight high frecjuency voltage amplification 

 of the set, as measured with resistance input to the grid of the first 

 high frequency amplifier. (Same as curve shown in Fig. 11.) 



Curve B gives the actual resistance of the loop used with the set. 



Curve C gives the resistance introduced in the loop due to "feed 

 back" action from the first stage. 



Curve D gives the resulting apparent resistance of the loop (Curve 

 B + Curve C) and 



Curve E shows the "feed back" amplilication of the set. (Curve 

 B: Curve D.) 



Curve F shows the total amount of amplification obtained by the 

 set which is the product of the orrlinarx- voltage amplification (Curve 



DM 



|Cb 



(a) 



iCg-p 



I-6MWWV — I 



I WMAM 



- (b) 



Fig. 13 — Schematic of Balancing Condenser .\riion 



A) and the "feed back" .uiijjlific.itioii (Curve E) and it is thus seen 

 that the feed back action makes the total amplification vary irregu- 

 larly in a very undesirable manner, and also makes the set "sing" at 

 certain frequencies. 



In order to avoid this, it is necessary to provide some means of 

 balancing out the effect of the grid plate capacity of the tubes, and 

 Fig. 13 (a) shows how this may be done.* The filament of the tube 



♦See Patent No. 1,183,875 issued to R. V. l,.'Hartlev. and Patent No. 1,334,118 

 iwued to C. VV. Rice. 



