VACUUM TUBE OSCILLATORS 



515 



If fiiiTny considerations alone determined the stability of the 

 oseillalinK sNsteni, it would apix-ar that liu' o|)eratin>; ()oiiil iniglu 

 he anywhere alon.u this line. It is necessary, however, to considiT 

 the phase displacements occurring in the two units as well. The 

 phase difference between the voltage across the output resistance of 

 the frequency control unit and the voltage impressed across the 

 junction .1 varies with frequency as indicated by the family of curves 

 shown in Fig. 7. The assumption is made in drawing these curves 



Fig. 



-Families showing relation between phase flisplacenient and fre<|uency for 

 various power le\cls 



that the change in damping is due entirely to a change in the resist- 

 ance of the coil and that the inductance and the natural fretjuency 

 of the circuit are unaltered as the load is increased. Ff)r low damp- 

 ing in the resonant circuit the phase shift changes rapidly with fre- 

 quency in the neighborhood of the resonance point. As the ampli- 

 tude of the voltage across the junction A is increased, thereby 



