Patent GB-317005-A (GB)
Title: Electric signal wave amplifying and translation systems
IPC: H03G9/08
Filed: 1929-07-22
Abstract: 317,005. Standard Telephones & Cables, Ltd., (Assignees of Black, H. S.). Aug. 8, 1928, [Convention date]. Induction, preventing and minimizing.-The invention relates to thermionic valve amplifiers as used in voicefrequency telephone repeaters, carrier-wave amplifiers for multiplex system, public-address systems, or for reproducing broadcast programmes or music from gramophone records or as power amplifiers for linewire or radio transmission. In general the invention is designed to reduce modulation cross-talk, or other distortion components, by isolating the distortion components from the fundamental signal wave, and feeding-back to the input a distortioncompensating voltage independent of the impedance in the output circuit through a path that involves no phase-change. In this way the fundamental wave energy is amplified without distortion, the gain ratio is stabilized and is made independent of variation in the valve power supply, and the load-carrying capacity of the system is increased without sacrificing either " gain " or efficiency. Fig. 1 shows a method of deriving a voltage Ae across resistances KRO and KR, which is directly proportional to, and in phase with the drying-voltage e in the plate circuit of an amplifier (the resistance of the space discharge path being represented by RO), and independent of the impedance of the work circuit (represented by Z). Fig. 2 is an equivalent circuit in which the impedances KRO and KR are shunted by an impedance. RS. Fig. 3 shows the application of the invention to a single stage amplification. The load impedance Z of Figs 1 and 2 is represented by the output transformer 2. The impedance RS of Fig. 2 now comprises the secondary to-primary mpedance RO1 of the input transformer 4, a resistance or impedance X, and a series of blocking condenser 9. It is shown mathematically that if X is made equal to R + RO ¸ Á no voltage feed-back takes place of the fundamental wave, though distortion components (which are present in the plate circuit and not in the grid) are negatively regenerated. In the arrangement shown in Fig. 6, the distortion components are isolated from the fundamental wave and are separately amplified and fed back through an auxiliary tube 1c. A resistance 15<1> is included in the input circuit of sufficient value to make the impedance of that circuit 2 substantially a pure resistance. The effective feed-back path from output to input comprises a blocking-condenser 9, the impedance X, and the effective impedance RO1 of the input transformer 4. The condenser 9 and coupling impedance RT of the tube 1e are of high impedance to the fundamental frequencies to be amplified. Distortion components however create an input voltage across the impedance RT which is amplified by the tube 1e and applied in opposition to the original distortion components present in the plate circuit of the tube 1a. As no appreciable negative regeneration is applied to the fundamental wave, there is no reduction in " gain," and the load-carrying capacity of the system is accordingly increased. Both odd and even order harmonics or distortion components are reduced simultaneously. In alternative arrangements the function of the amplifier 1e of Fig. 6 is performed by an auxiliary grid in the first amplifying tube. A circuit arrangement is also described for amplifying a plurality of signals simultaneously for multiplex carrier working. This comprises five stages of signal amplification in tandem the last stage comprising two parallel valves in push-pull with two other valves in parallel. Two stages of auxiliary amplification are provided for handing the isolated distortion components. The invention increases the loadcarrying capacity of the amplifiers not only by suppressing distortion components, but also by regenerating the fundamental waves in such a way as to control " gain " to an optimum degree.