TRIANGULAR WAVE GENERATORS 



CR are altered together. If C'R' is too small the circuit will not work at all, 

 or will give only a small output. If C'R' is too big the output has the form 

 of Figure 16.22. 



Figure 16.22 



Phantastron 



In this circuit one valve is used to its utmost; not only all three grids and 

 the anode, but also the cathode fluctuate in potential to contribute to the 

 action. Stripped of unessentials, the circuit has the appearance of Figure 

 16.23. Ri, i?2 and ^3 are merely a potential divider across the HT supply to 



Figure 16.23 



define the potentials of suppressor and control grid when the circuit is quies- 

 cent. Notice the catching diode, which allows the control grid to move 

 negative with respect to the junction of R^ and R^, but not positive. 



Before the arrival of the trigger pulse screen current flows and by cathode 

 follower action the cathode is shghtly positive with respect to the control 

 grid. As a result of the voltage drop along i?2 the suppressor is considerably 

 more negative and in consequence anode current is cut off". On the arrival of a 

 positive trigger, the suppressor potential is raised, allowing anode current to 

 flow. Vertical fall occurs at the anode and is communicated to the control 

 grid via C and to the cathode by cathode-follower action. Since control grid 

 and cathode have fallen it is as if the suppressor potential had been raised, 

 and Miller run-down can proceed even though the trigger pulse has come to 

 an end. 



17 



245 



