illustrated in fig1 through a coupling network 73 as can be seen from fig2 the integral control consists of an operational amplifier 71 which together with a capacitor 72 forms an integrator an input of the operational amplifier 71 is supplied with the normal magnitude signal thus with the output signal of the two amplifiers 61 and 62 wherein in addition at this input a reference voltage vr is connected through the coupling network 73 a variation of the output voltage of the two amplifiers 61 and 62 from the reference voltage vr effects a control operation or the occurrence of a control signal at the output of the amplifier 71 the control signal is fed through a mos field effect transistor 81 to a capacitor 91 which corresponds to the buffer store 9 illustrated in fig1 the mos field effect transistor 81 forms the switch 8 illustrated in fig1 it has an insulated control electrode and thus does not contain seen from the outside a diode path in any possible current direction the already described amplifier 10 is connected after the capacitor 91 which amplifier 10 is advantageously a high ohmic field effect transistor amplifier the output signal of the amplifier 10 is fed to the two control electrodes of the field effect transistors 43 and 44 if the capacity of the capacitor 91 was for example 1000 pf a time constant of 5 sec could be produced the mos field effector transistor 81 is controlled at its control electrode by a signal which is taken from the threshold circuit 11 illustrated in fig1 the threshold circuit consists as illustrated in.