Abstract: In a self-oscillating mixing stage for FM radio receivers, comprising a transistor producing the oscillator signal and to whose emitter circuit the high-frequency signal is coupled and from whose collector circuit the intermediate-frequency signal is coupled out, the transistor being operated in the grounded-collector circuit mode to produce the oscillator signal and in the grounded-base circuit mode to process the high-frequency and intermediate-frequency signals.

Abstract: A detector suitable for use in a recording amplifier of a cassette recorder for limiting the signal which is applied to the write head at a specific average amplitude. The detector comprises a pre-amplifier T1 to T4 having an input (15) and an output (17); a comparator (T6) having a first input (base) coupled to the output of the pre-amplifier, and a second input (emitter) for detecting whether a detection voltage at the second input is exceeded by the voltage on the first input of the comparator circuit; a reference voltage source (V.sub.ref); first means (4) for maintaining the d.c. level at the output of the pre-amplifier (T1 to T4) at the level of the reference voltage source (V.sub.ref); and second means (T10, T11) for raising the detection level of the comparator circuit by the reference voltage.

Abstract: By using a optical switch, which can be operated by the tuning knob of a receiver, signals can be obtained which accurately correspond to the operation of the tuning knob for switch-over of the receiver to a continuous manual tuning mode and for suppressing the automatic tuning correction during tuning.