GB886971A - Improvements in or relating to amplitude sensitive circuit arrangements - Google Patents

Abstract

886,971. Circuits for gramophone reproduction. PHILIPS ELECTRICAL INDUSTRIES Ltd. April 15, 1959 [April 18, 1958], No. 12810/59. Class 40 (4). [Also in Group XL (c)] A circuit arrangement suitable for indicating overload in a radio receiver or gramophone amplifier comprises two valves, a common input for supplying an input signal to the two control grids, a low anode voltage supply for the second valve, the second valve being biased to cut-off by a bias which is developed across the cathode resistor of the first valve and applied to the cathode of the second, whereby, on the occurrence of a peak of predetermined amplitude at the input the second valve is made conducting. In the Figure, the detector 7 of a radio receiver is shown feeding a tuning indicator 17 and an audio amplifier 10, the amplifier 10 driving the triode 16 output stage. An additional triode 15 has a common grid and cathode connection with triode 16. A low-voltage anode supply for triode 15 is derived from resistors 19, 22, so that the cathode bias keeps the valve normally cutoff, and the output is connected to the grid of a tuning indicator 17 via capacitor 21. When the positive half-cycle of the audio waveform reaches an amplitude at which the grid of valve 16 is driven to zero or positive with respect to cathode, valve 15 conducts and produces a signal across resistor 19. This signal is applied to the tuning indicator 17 to be superimposed as a flutter on the visual tuning signal. The signal output from valve 15 may be alternatively applied to the grid of the tuning indicator by a transformer.