866,937. Frequency amplitude/modulation receivers. GENERAL ELECTRIC CO. Ltd., and COMLEY, D. A. April 17, 1959 [April 22; 1958], No. 12721/58. Class 40(5) A superheterodyne f.m./a.m. receiver wherein the output of the intermediate frequency amplifier 1 is connected in series with the resistance 4 and capacitance 5 connected in parallel between the control grid and cathode of a pentode 3, a switch 10 being provided for rendering the anode circuit of valve 3 operative (as shown) for the reception of f.m. waves or inoperative (in the other position) by the insertion of a high resistance 9 in the anode circuit, so that in the former case the valve operates as an amplitude limiter the f.m. output of which is derived from ,the anode circuit through a ratio detector 14 and in the latter the control grid and cathode of the valve operate as a diode detector the a.m.; output of which is derived from the resistor capacitor combination 4, 5. Further switches 21, 15 and 24 are ganged with switch 10 so that, in the position shown (for f.m. wave reception) a high potential is applied to cut off crystal diode 17 and remove switch 15, resistor 18 and capacitor 19 from the control grid circuit and capacitor 23 is short circuited since A.G.C. for amplifier 1 is not necessary due to the limiting action of valve 3. With the switches in the a.m. wave receiving position, valve 3 acts as a diode as already stated and the audio frequency output is applied to the amplifier via capacitor 16, diode 17 and switch 15, diode 17 now being biased into conducting condition, due to its connection to H.T. through switch 21, and acting as a noise limiter.