Patent GB-769306-A (GB)
Title: Improvements relating to colour television receivers
IPC: H04N11/12
Filed: 1953-08-14
Abstract: 769,306. Colour television tubes; luminescent materials. VALENSI. G. Aug. 14, 1953 [Aug. 14, 1952], No. 22468/53. Class 39(1). [Also in Group XL(b)] A colour television receiver tube has a fluorescent screen comprising a blend of fluorescent substances such that colour is dependent on beam current density and brightness on beam velocity. Blue, green, deep red and bright red are imparted to the fluorescent colour blend by zinc sulphide/silver, zinc silicate /manganese, cadmium sulphide /silver and magnesium silicate /manganese respectively. In the receiver, Fig. 4, signals F<1> are fed to a separator 6 and a detector D. The signals trigger the horizontal and vertical scanning oscillators Sy of the receiver tube and also open a gate valve &c. which triggers an oscillator g supplying a reference signal of frequency F. The oscillator may be synchronized by a signal generated by the scanning. The detector D has two ouput circuits giving the brightness signal t and the coded colour signal T. The signal T is applied via a 3-way switch Com to a decoder tube TD fitted with a mask M, the output # being applied as a variable bias to the control grid of the receiver tube O. The brightness signal t is amplified by the valve l1, which feeds the power amplifier AP connected across the anode A and the cathode j of the tube O. When the switch Com is in position 2, a coded colour signal corresponding to white is provided by rheostat Rh, the ouput from the decoder tube TD giving black and white pictures in tube 1. Position 3 of the switch Com corresponds to the provision of colour signals of the sequential type. The terminals 3 are connected to the ouput of three diodes D1, D2, D3 having input from the scanning oscillator Sy and so combined with condensers k1, k2 as to give a stepped voltage wave-form. A dephaser device, Fig. 4a (not shown) is connected to give the correct colour sequence at will, and comprises a cathode ray tube with three anodes connected by a 3 pole switch to three resistances having values giving the correct colour code at the decoder tube TD. In position 1 coded colour signals T produce the appropriate control voltage # at the Wehnelt electrode of the receiver tube. The cathode ray tube is subjectively selected and analysed by photo-metric observation, Fig. 6. Light from red, green and blue projectors R, G, B, passes through a plate L of graduated transparency onto a roughened glass screen and is compared visually for brilliancy and colour with the light produced on fluorescent screen Fl for difference Wehnelt potentials # and anode potentials V. The relationship between the reciprocal of the brilliancy and the colour number on the Maxwell scale enables a colour filter to be prepared which, placed in front of the receiver tube, brings the minimum brilliancy of the screen to the same value for all colours. A thin deposit of pigments of blueish purple colour on a perfectly transparent glass plate is instanced. Similarly the apertured mask M is prepared from the curve relating the Wehnelt voltage # to the coded colour signal T and placed on the decoder tube TD. The photometer of Fig. 6 is also used to obtain for fixed values of #, the variation of brilliancy with anode voltage which enables a vacuum tube l1 to be selected having the correct gain characteristics to render the brightness insensitive to variations in beam current density. Specification 645,125 is referred to.