Patent GB-483451-A (GB)
Title: Improvements in or relating to electro-optical image producing systems, such as television systems
IPC: H04N5/16
Filed: 1937-08-26
Abstract: 483,451. Television. ELECTRICAL RESEARCH PRODUCTS, Inc. Aug. 26, 1937, No. 23379. Convention date, Sept. 2, 1936. Addition to 406,672. [Classes 40 (iii) and 40 (v)] Direct-current components are inserted under the control of correcting impulses ocouring in the picture signals by a circuit comprising a grid-controlled gas-filled discharge tube. The picture signals are amplified at 33, Fig. 1, and flow through the reconstituting lamp 38, a resistance 39 and a resistance 41 ; the potential across resistance 41 is reduced by a correcting impulse so that the negative bias on the control grid of the discharge tube 42 is lowered to allow the tube 42 to discharge ; the discharge current charge condenser 50 to reduce the anode potential to inhibit the discharge of tube 42 ; resistance 52 and condenser 51 smooth the voltage applied to amplifying valve 49 whose output is applied to the screen-grid of valve 33, so that the anode current of valve 33 depends on the correcting impulses. The resistance 39 is of the material known under the Registered Trade Mark " Thyrite " which has the property that increasing current is accompanied by a reduction of the voltage across the resistance, whereas the neon lamp 38 has an opposite characteristic ; the combination of the two in series results in a linear relationship between the current and voltage. In a modification, the gas discharge tube 87, Fig. 6, is ignited by the potential across resistance 81 in the output circuit of the final picture signal amplifier 70; the tube 87 charges condenser 93 to inhibit its own discharge, and its output is amplified at 76 and applied over smoothing elements 74, 98 to the grid of valve 70 ; the valve 85 only serves to improve the regulation of the supply 80. The gas discharge tube may be energized with alternating current on its anode, its output being amplified, rectified and applied across the grid condenser of the final picture signal amplifier, Fig. 7 (not shown). Alternatively, the gas discharge tube may control a relay whose armature controls the supply of current impulses applied over a smoothing circuit to the grid condenser of the final amplifying valve, Fig. 8 (not shown). The gas discharge device 199, Fig. 9, may oscillate under the control of alternating current 60 applied to both input and output circuits ; when energized by a correcting impulse its discharge current increases, the voltage across condenser 194 increases while the voltage delivered by coil 192 is decreased ; the rectifier 195 thus produces a lower voltage across resistance 189 which modifies the bias on the final amplifier 188 to increase its output. In a further modification, two discharge tubes 216, 219, Fig. 10, are energized with alternating current on cathodes and anodes, the correcting signals being applied in parallel to the grids so that the outputs consist of pulses whose duration is dependent on the correcting signals ; these are applied over transformers 229, 230, to control two mercury vapour rectifiers 244, 245, in push-pull whose output is smoothed and applied in the output circuit of the amplifier 260, in series with the lamp 38. British Specifications 357,049, [Group XXXV], 406,672, and U.S.A. Specification 1,822,742 are referred to. According to the Specification as open to inspection under Sect. 91, the direct current component may be inserted by circuits employing thermionic valves. The picture signals are applied from amplifier 160, Fig. 9 (Cancelled) to a valve 164, feeding an amplitude filter 169 whose output is smoothed and applied to bias the final amplifier 175 also fed from amplifier 160. The parallel path formed by 164, 169 may be replaced by a valve biassed to select the peaks of the correcting signals and an amplifier, Fig. 16 (Cancelled) (not shown). Alternatively, the direct current may be reinserted by a second valve feeding the neon lamp, to which the bias derived from the correcting signals is applied, Fig. 17 (Cancelled) (not shown). The isolated correcting signals may control a relay whose armature controls the supply of impulses applied to a smoothing circuit for biassing the final amplifier, Fig. 18 (Cancelled) (not shown).