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BELL SYSTEM TECHNICAL JOURNAL 



amplifier using the nominal Type A transistor adjusted in this way gives 

 the following results: 



Assuming an adjusted value of collector resistance of 36000 ohms to be 

 satisfactory for stability, then the iterative input impedance is 2300 ohms, 

 output impedance 4000 ohms, and insertion gain about 21 db per stage with- 

 out transformers. Three-stage stable amplifiers having power gains of about 

 55 db have been operated. 



Without feed back i^ln = 0): 



Iterative impedance Rg = ^22/<p^ Rl = fjlu 



Circuit determinant A = (9\u "1- 9^22/'^^)- 





Insertion Power Gain G/ = 



Maximum when f-j^u = f-)\22/V 

 G/ 



9in _^yj^^- 



Nominal Type A Gain: without feed back = IS''* 

 with 9vi2 normal = 17''* 



Fig. 18 — Synopsis of grounded base cascade with transformers. 



Another interesting feature of the grounded emitter amplifier is the ease 

 with which negative feedback may be applied to it. A resistor inserted in 

 the emitter lead gives local negative feedback analogous to the cathode 

 feedback of tubes, while feedback mvolving several stages is also obtainable 

 by common-lead methods analogous to common-cathode resistors familiar 

 in the tube art. By such means, as is well known, distortion instability or 

 gain variation may be reduced, or power output increased. 



Theoretical study of these and other iterative amplifiers, particularly at 

 higher frequencies, is conveniently carried on with the aid of the formulas 



