1324 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



sis tor may appear to have zero resistance in the emitter to base circuit 

 or a small positive or negative resistance. 



It is evident from the foregoing that the abiUty of a transistor to fulfill 

 the requirements for oscillation is therefore dependent upon both the 

 average a along the load Une and, R\^ resistance in region 1. The rela- 

 tionship of these two factors is shown in Fig. 7. Dots on this chart repre- 

 sent the 1729 type transistors tested that met the requirements for the 

 2N25 transistor. The ambient temperature was +135°F. It is inadvis- 

 able to use transistors having a resistance of much less than 4000-ohms 

 in region 1 since both the average dissipation rate and the peak dissipa- 

 tion rate would exceed allowable limits for continuous operation. This 

 will tend to cause the transistor characteristics to change at a more 

 rapid rate. 



The effect of different values of feedback on the output of the oscillator 

 is shown in Fig. 8. Fig. 8 also shows the variation in output obtained 

 \vith several different values of load resistance. This was done to illus- 

 trate the use of increased load in determining the proper point for ad- 

 justing the feedback resistance. The proper adjustment is the minimum 

 feedback with which the output changes only approximately 1 db in 

 going from normal load to four times normal load. This degree of margin 



10^ 



20 



O I 



z \- 



^5 



lij !=: 



cr U) 



. liJ 



o tr 



1^ 



z o 



liJ ^ 

 < p 



f^ ff. 



8? 



0.4 



0.8 



2.4 



2.8 



1.2 1.6 2.0 



AVERAGE a, ALONG LOAD LINE 



Fig. 7 — Plot of a versus collector to base resistance for representative group 

 of transistors meeting 2N25 transistor requirements. 



