10 000 ohms and resistor r12 is about 1 600 ohms the second current source comprises an npn transistor q1 whose collector is coupled to the positive side of capacitor c3 whose base is coupled via resistor r8 to the output q of flip flop ff1 and to ground via resistor r9 and whose emitter is coupled via resistor r13 to ground by way of example transistor q1 is a pn 2222a transistor resistor r8 is about 18 000 ohms resistor r9 is about 10 000 ohms and resistor r13 is about 390 ohms transistors q1 and q2 are selected so that their characteristics are complementary and along with resistors r9 through r13 cause the circuit to operate with a constant duty cycle during operation the circuit is in its first or stable state when flip flop ff1 is in its reset position and its output signal is approximately six tenths of a volt or less with the output q of flip flop thus low transistor q2 is conducting a positive bias voltage from supply voltage vcc via resistor r11 applied to the base of transistor q2 keeps it turned on so that current flows from the emitter to the collector of transistor q2 and.