STIMULATORS 



RF oscillator might well be included within the body of the stimulator so 

 that the coupler unit or 'RF probe' now only contains the secondary circuit 

 and rectifier components; the two are joined together by a single coaxial 

 cable carrying RF power. In this manner a much smaller and neater probe 

 becomes possible. 



This has been done in the author's stimulator, one channel of which is 

 shown in Figure 38.9. A Miller transitron oscillator feeds flip-flop No. 1, 

 whose negative going square wave output from anode No. 1 is used to 

 brighten and trigger the trace of a Cossor 1049 oscilloscope. The leading 

 edge of the positive going square for anode 2 wave is differentiated to trigger 

 flip-flop 2, which is the delay circuit. At the end of the delay period flip-flop 

 No. 3 generates the requisite stimulus pulse and passes it to a cathode follower. 



f V Via grid 



/V 



1^20 anode -bright up 



waveform 



V2b anode 

 Vza grid 



delay 

 period 



Vja anode 



■^''^Spike removed by 

 I crystal diode catcher 



I N. V^o grid 



y 



Shock 

 pulse 



14^ anode 



and Vc, cathode 



Co-axial cable 



Output of RF probe 

 Figure 38.18 



A shock amplitude control follows, and transfers the pulse as HT to the 

 oscillator circuit, which is a modified series-fed Hartley. The modification 

 consists in bringing out the oscillator tuned-circuit circulating current 

 through coaxial cable to a single-turn coupling coil in the RF probe. The 

 repetition frequency of this stimulator ranges from 1,000/sec to 1 shock 

 every 35 sec. The maximum delay is 250 msec and the pulse duration is 

 variable between 100 /isec and 100 msec. The shock amplitude is adjustable 

 in the range 0-40 V. Waveforms are sketched in Figure 38.18. 



614 



