GB227189A - Improvements in receiving sets for wireless signalling - Google Patents

Abstract

227,189. Turner, J. M., and Soundy, L. H. Oct. 10, 1923. Thermionic amplifiers and detecters. - Valve receiving-sets are operated by alternating or direc current from supply mains &c., and noises due to the alternations or fluctuations are .eliminated by a combination of (1) a smoothing device in the plate supply circuit comprising series chokes and shunt capacities; (2) a potentiometer across the filament terminals with a sliding contact connected to the grid; and (3) a coupling between the anode and grid circuits of the detector valve and means for giving the grid sufficient positive charge to operate at the top bend of the characteristic curve. A composite air-cored and iron-cored choke may be connected in the filament circuit. Fig. 5 shows the circuits for a multi-valve set using alternating supply current, and Fig. 6 the corresponding circuits for direct current. The set comprises a high-frequency amplifier 49, detector 48, and lowfrequency amplifier 50. The supply transformer 38 has three secondary windings, coil 39 supplying the high tension to the plate circuits, coil 41 supplying the valve filaments, and coil 40 supplying the filaments of rectifiers 36, 37. The plate current is drawn from a condenser 42 through chokes 46, 46<1> followed by a shunt condenser 42<1>. The filament current, passes through an air-cored choke 64 and iron-cored choke 64<1> and through separate rheostats to the several filaments. Across each filament is connected a resistance with a tap connection to the grid circuit, condensers being shunted across each section of the resistance. Alternatively the grid circuits can be connected by a lead 65 to a centre tapping on the coil 41. The grid 53 is given a positive charge either by a battery 55 connected to a leak resistance 56, or by a battery 52<1> connected to the grid through the tuned high-frequency circuit 52, 52<1>. In the latter case, the grid condenser 57 is omitted. A coil 62 in the tuned plate circuit of the detector 48 is coupled to the grid coil 52. An air-cored choke 47 wound in sections is connected between the plate of the high-frequency amplifier and the primary coil of the transformer in the detector plate circuit. A condenser 66 is inserted between the aerial inductance and earth. When direct current supply is used as shown in Fig. 6, the filament supply is taken from the mains 74, 75 through a@ adjustable resistance 69, iron-cored chokes 67, 68 and a composite air-cored and iron-cored choke 64, 64<1>. An adjustable tapping 70 on the resistance 69 is connected through a choke 46 to the plates, and smoothing-condensers 72, 73 are connected across the plate and filament leads before and behind the chokes 46, 68. When a fourelectrode valve is used for detection, the inner grid is given a positive charge. and the input oscillations are applied to the other grid.