COUNTERS 



capacitor to the first guide, tlie glow transfers one electrode round the ring: if 

 a fraction of a second later a similar negative pulse is then applied to the 

 second guide, the glow advances a step further. At the conclusion of the 

 second pulse the glow is nearer to the n -{- Ith cathode than to the nth, 

 and in consequence moves forward once more, thus accomplishing one 

 count. At the completion of each ten counts the glow passes the output 

 cathode, and a positive pulse is developed across the load resistor by the 

 passage of the glow current through it. 



HT+ 



Input ^ 1 1 



"LT 



Figure 41.14 



The GC 10 B is, for obvious reasons, called a 'double pulse' dekatron, 

 and driving it is seen to be a matter of providing two negative pulses in 

 quick succession. This may be done in a number of ways; in most of them 

 a negative pulse is applied directly to the first guides and via a low-pass 

 filter to the second, as in Figure 41.14. With properly chosen values the 

 waveforms are then as sketched in Figure 41.15. 



Input and first guides 



Second guides 

 Figure 41.15 



The output pulse from one dekatron is in the wrong phase and of 

 insufficient magnitude to drive another. A circuit recommended by the 

 manufacturers which eff'ects the necessary phase reversal, amplification 

 and double pulse production is shown in Figure 41.16. It makes use of 

 the high-speed trigger-tetrode type GTE 175M, which is convenient in that 

 no cathode heater power is required. 7 his circuit works up to 500 counts/sec. 



The GC 10 D — This high-speed dekatron has 40 electrodes equally 

 spaced around the anode, made up of 10 cathodes and 3 sets of guides. 

 All first guides are brought out together as one connection, and all second 

 guides as another. The third guides are divided, as are the cathodes, into 

 output third guide and all other third guides, and output cathode and all 

 other cathodes: the output third guide, of course, precedes the output 

 cathode. The gas filling appears to be argoa The circuit diagram is as in 



651 



