SYNCHRONIZED SOUND PICTURES 



189 



of tubes Vi and Vi negative. This in turn reduces the plate current 

 through tubes Vi and Vi and hence through the D.C. winding of 

 the inductance Li controlHng the armature current of the motor. 

 Tube Fs is a rectifier tube supplying excitation to the field of the 



i-C. CONTROL CABINET 



Fig. 5 — A. C. control circuit diagram. 



(Qz: 



3LLJ 



q: 

 ^o 



H^ 

 1-2: 



Id CO 

 Q 



^ 



Fig. 6- 



FREQUENCY 



-Characteristic of space current through detector tube Vi. 



720-cycle alternator and the negative "C" voltage along potenti- 

 ometer Pi. 



Fig. 7 shows the performance characteristics of the motor. It will 

 be noted that the actual speed characteristic is practically flat. This 



