Abstract: To actuate a complementary push-pull class B final stage complementary driver transistors are provided whose emitters are electrically interconnected and connected to the collectors of the two final stage transistors via a filter section. This filter section is not integratable into the rest of the circuit on account of the high capacitance value of the capacitor. To permit design of this complementary push-pull class B final stage as an integrated circuit the filter section is replaced according to the invention by a circuit arranged between the emitters of the driver transistors and ground and having dynamic low impedance and being designed such that the operating voltage drops by about half across the integratable circuit.

Abstract: The invention relates to a low-frequency amplifier with an integrated push-pull B final stage and a circuit for adjusting the quiescent current. The invention resides in the amplifier comprising two circuits for adjusting the quiescent current which are provided for different voltage ranges of the supply voltage. An electronic switchover device ensures automatic activation of that circuit for quiescent current adjustment which is suited for the respective voltage range.

Abstract: Feed-back paths of amplifiers, such as the alternately-operable AM and FM amplifiers of radio receivers, are interconnected by a first capacitor and earthed by a second capcitor, and each of the paths has a switching transistor for permitting current flow through only the feed-back path of the amplifier which is in operation. The AM amplifier has several stages including a final stage with transistors connected via respective feedback paths to two respective input connections. The FM amplifier is identical except that the component values differ.

Abstract: A mixer/oscillator circuit comprises a mixer stage to which an oscillator stage is connected, an emitter follower circuit being connected between the oscillator stage and the mixer stage.

Abstract: A circuit for controlling a current source transistor in dependence on a d.c. supply voltage comprises a further current source connected to the d.c. supply voltage source, and supplying a component with current, the control voltage for the current source transistor dropping across the component and a resistor controllable in dependence in the d.c. supply voltage and connected in parallel with the component.

Abstract: A circuit for at least two frequencies comprises a high frequency filter and a low frequency filter and a pair of series connected terminating resistors, the high frequency filter being connected to a first terminating resistor and directly to a common circuit point, the low fequency filter being connected to the connection between the two resistors and the order of magnitude of the terminating resistors being the same as the order of magnitude of the required terminating resistance of the filters.

Abstract: An electronic cut out for the protection of output stage transistors of a low frequency amplifier comprises means for producing first and second direct voltages proportional to the output alternating voltage and the collector alternating current of the output stage transistors respectively, means for comparing these voltages and igniting a thyristor if the second voltage exceeds a predetermined threshold, the thyristor being connected to short circuit the low frequency signal to earth prior to its arrival at the output stage transistors when the thyristor is ignited.