1,129,142. Electromedical apparatus. MEDICAL & BIOLOGICAL INSTRUMENTATION Ltd. 25 May, 1966 [26 May, 1965], No. 22444/65. Heading A5R. An electric muscle stimulator includes a circuit comprising a surging wave-form generator 1, a square wave-form generator 3, a mixing stage 5, including transistors T 6 , T 7 , for the outputs of the generators and an output stage 7, the output of the circuit including square wave signals in bursts controlled in the mixing stage 5 by the surging wave-form generator output. The surging wave-form generator 1 comprises a free-running transistor multivibrator T 1 , T 2 and the square wave-form generator 3 comprises a free-running transistor multivibrator T 3 , T 4 , the feedback voltage of which is increased by an emitter follower stage T 5 in its output. The multivibrator T 1 , T 2 and the emitter follower T 5 are connected by leads 22, 35 respectively, to the bases of series-connected transistors T 6 , T 7 on the mixing stage 5, the output of which is developed across a potentiometer 37. The output stage comprises transistors T 8 , T 9 and is connected through a transformer 40, 41 to a circuit including an applicator pad or pads 42. The output (Figure 2(c)) comprises square waves (Figure 2(b)) which are 'on' for 200 microseconds and 'off' for 15 milliseconds, within an envelope (Figure 2(a)) in accordance with the surging wave output which has a leading edge of gradually increasing amplitude and is 'on' for 750 milliseconds and 'off' for 750 milliseconds.
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