GB403283A - Improvements in or relating to television apparatus, synchronising apparatus and thelike - Google Patents

Abstract

403,283. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Tolson, W. A. ; 631, Jefferson Avenue, Erlton, New Jersey, U.S.A.) May 1, 1933, No. 12639. Convention date, April 30, 1932. [Classes 40 (iii) and 40 (v).] A saw-tooth current 40 for deflecting a cathode ray 15 is generated by a back-coupled thermionic blocking oscillator 20 with a shaping circuit 34 in its output circuit to produce a voltage wave 39, which has a saw-tooth component and a component of short impulses separated by relatively long intervals and is applied to a single amplification stage 38. The valve 20 produces periodic current impulses by back-coupling through a transformer 21. Grid-current, flowing during the impulse, accumulates on a grid condenser 22 to prevent another impulse until the charge has leaked away through a high resistance 24. The values of the grid leak and condenser are such that the impulses are generated at the line-scanning frequency, the impulses being synchronised by positive signals applied to the valve through a filter 32. A condenser 35 and a resistance 37 are connected in the output circuit of the valve, and the voltage wave developed across this network 34 has the form 39. This voltage, applied to the grid of the valve 38, gives rise to the saw-tooth current 40, which passes through deflecting-coils 17 of a cathode-ray tube 10. A saw-tooth current of the picture frequency is generated by a similar circuit 30a, and passed through deflecting coils 18 to give the other component of scanning. According to modifications : the resistance 36 is connected across the condenser 35, Fig. 2 (not shown) ; a screen-grid valve is used as the generator, Fig. 3 (not shown) ; negative synchronising impulses are used, Fig. 4 (not shown). Specifications 395,499 and 402,629 are referred to.