148 



DELL SYSTEM TECHNICAL JOURNAL 



reduce the space current lo zero. The condenser C continuously' 

 discharges through the resistance ra. The niejui potential on the 

 condenser is thus applied to the grid of the vacuum tube and modifies 

 the space current, which, in turn, is passed through the damping coil 



^iih-L-ih-— iK-*l •h-^l'l'h^h--*H 



Fig. 1 — Clock Control of I'ork Kric|iRMuy 



of the fork. A stable cimdition is rtMched when the condenser dis- 

 charge each second is exactly equal to the charge. Any \ariation in 

 the condenser potential varies the current through the damjiing coil 

 and changes the frequency of the fork. Now if the period, during 

 which the relay remains operated, increases, the mean potential on 

 the condenser will gradually increase. This will increase the mean 

 negative grid potential, reducing the mean space current through the 

 tube anil through the damjiiiig winding, thus reducing the damping on 

 the fork and increasing its fre(iuency. 



