GB493667A - Improvements in or relating to amplifying systems for modulated high-frequency oscillations - Google Patents

Abstract

493,667. Valve amplifying circuits; impedance networks. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. Oct. 19, 1937, No. 28510. Convention date, Oct. 22, 1936. [Classes 40 (iii) and 40 (v)] A system for amplifying modulated highfrequency currents comprises four valves 21, 22, 33, 34, of which the valve 21 is biassed to bottom bend, the second valve 22 is biassed so that it only passes anode current when the carrier amplitude exceeds a datum value less than the mean carrier, whilst the other two valves 33, 34 are biassed equally and to such extent that anode current only passes when the carrier exceeds a datum value greater than the mean carrier. The load impedance L is connected in series with the terminals 5, 6 of an impedance-inverting network 7, the output terminals of an impedance-inverting network 11 fed by the valve 34, and with the output coupling of the valve 21. The other terminals 8, 9 of network 7 are connected in series with a network 10 associated with the valve 33 and with the output coupling of the valve 22. The surge impedance of the networks 10, 11 is half the surge impedance of the network 7, and the latter is half the load impedance L. The carrier is supplied to the grid circuits of the four amplifiers in such phase relation that after the phase changes produced by the networks, the load L is fed in the same phase by all the amplifiers. This is effected by applying the carrier to the grids of valves 22, 33, 34 at phase angles displaced by 90‹, 180‹, and 90‹ respectively with relation to the carrier applied to the grid of the valve 21. The anode circuits 31, 32 of the amplifiers 21, 22 are parallel-tuned and inductively coupled to a coil 41, 42 in series with a condenser 51, 52. The network 7 comprises series condensers 57, 57<1> and a shunt coil 47 all of the same reactance at the carrier frequency. The networks 10, 11 comprise coupled inductances 43, 43<1>, 44, 44<1> all of which are series-tuned to the carrier frequency by condensers 53, 53<1>, 54, 54<1>. The condensers located in the same circuit may be united to form a single unit. Push-pull valve pairs or parallel-connected valve groups may be used in each of the amplifiers. In a modified system, the load impedance L is connected across the terminals 8, 9 of the network 7, and the surge impedance of the network 7 is double that of the load, Fig. 4 (not shown). The Specification also refers to a known system, Figs. 1 and 2 (not shown), employing only two amplifiers one of which feeds the load directly and operates at all values of carrier, whilst the other feeds the load through an impedance-inverting network and operates only when the carrier rises above its mean level. This system improves the energy-conversion efficiency as compared with the usual single amplifier, and efficiency is further increased by the four-amplifier system of the present invention. Specification 471,423 is referred to.