TRIGGERED PULSE GENERATORS 



via C, reducing the cathode potential and hence tending further to increase 

 the current in V^. The result is the now-familiar cumulative action, as a 

 result of which Kg becomes cut off and V^ heavily conductive. 



Current now flows via R into the right-hand plate of C, causing V^ grid to 

 rise exponentially towards the potential of the slider of P. At length, con- 

 duction begins again in Fg, initiating a cumulative action in the reverse 

 direction, re-cocking the circuit in its original state. Waveforms are sketched 

 in Figure 16.4. An output may be taken from either anode according to 



1 



^ grid 



Level at which 

 grid is 'caught' 

 by diode action i 

 in 16~ 



Level — /■ 

 at which/ 

 conduction 

 begins in 



V, anode 



■-'-"7 



Level of P 



slider 

 Vi grid 



V2 anode 



Figure 16.4 



the polarity required. The duration of the pulse may be controlled by varying 

 R, C, or the slider of P. The amplitude of the pulse depends on the valve, 

 the HT, and is related to the ratio of the relevant anode load to R^. The 

 pulse duration also depends on these three quantities. A high rate of rise 



Figure 16.5 



and fall at the beginning and end of the pulse is secured by having the anode 

 loads low and by minimizing shunt capacitances, particularly by using 

 pentodes {Figure 16.5). Remember that the screens have to be decoupled to 

 the cathode, since pentode action depends on stabilizing the screen cathode 

 potential difference. 



Triggered transitron 



Just as the flip-flop is a biased cathode coupled multi-vibrator, the triggered 

 transitron is a biased version of the transitron oscillator. The latter does 



236 



