GB464553A - Stabilisation of television amplifiers - Google Patents

Abstract

464,553. Valve amplifying circuits. RADIOAKT.-GES. D. S. LOEWE. July 24, 1936, No. 20555. Convention date, July 25, 1935. [Class 40 (v)] In order to prevent picture flicker in a television system the amplifier for the picture signals is compensated against back coupling due to the impedance of the supply source. As shown, the amplifier comprises a preliminary stage 3 coupled to the photo-cell 2 followed by a chain of resistance-capacity coupled amplifiers, the whole being supplied with anode current from a mains rectifier 6 and smoother 7, 33. The output stage 5 of the amplifier is coupled through a potential-divider 16 to a compensating valve 13, the arrangement being such that the anode variations of the valve 13 are equal in amplitude but opposite in phase to those of the valve 5. Under these conditions the signal current in the valves 5, 13 does not produce any voltage drop in the supply unit, and is therefore not fed back to the grids of earlier valves through the lead 8. Grid bias for the valves 5, 13 is fed from a resistance 23 through a filter 34, 35. Further resistance-condenser filters 9, 10 ; 11, 12 may be employed between the anode lead 8 and the earlier valves. The valve 13 may be used to give a negative picture if the valve 5 gives a positive picture. Loss of high frequencies in the coupling between the valves 5, 13 may be controlled by a variable condenser 21. The Specification as open to inspection under Sect. 91, includes the method of decoupling for screen-grid valves described in Specification 468,350. This subject-matter does not appear in the Specification as accepted.