Hence, it can be seen that the voltage at the point 58 of the circuit varies between the voltages of the median points between the resistors 51 and 52, on the one hand, and 52 and 53, on the other, or in other words between 8 and 4 V. The period of sawtooth voltage thus obtained is a function of the charging time of the capacitor 65, and this symmetrical sawtooth voltage is applied to the negative