GB585419A - Improvements in or relating to valve amplifiers - Google Patents

Abstract

585,419. Photo-electrically controlled amplifiers. GALL, D. C. Aug. 4, 1944, No. 14973. [Classes 40 (iii) and 40 (v)] [Also in Group XXXVI] In an amplifier employing a galvanometer responsive to the voltage to be amplified and having a zeroising feed-back from a gasdischarge valve or relay controlled by a photoelectric cell actuated by light from the mirror of the galvanometer and in which the relay has A.C. voltages applied to its anode and grid as described in Specification 537,784, means are provided for adjusting the relative phase of the voltages appearing in the grid and anode so that the relay affords an output representative of the input voltage to be amplified and does not oscillate readily. An A.C. feed-back to the galvanometer is also provided for preventing oscillations developing in the case of sudden movement of the instrument. In the drawings 1, 2 are the terminals over which the input voltage is applied to galvanometer G. Zeroising feed-back is derived from resistance 3 in the anode circuit of relay 5, which,has A.C. voltage applied to its grid and anode from windings 13, 19 of transformer 14, the phase of the voltage appearing on the grid being controlled by condenser 21 and resistance 22, one or both of which is or are adjustable, and by the impedance of the photo-electric cell 23. The adjustment is such that within the range of impedance variation of cell 23 the relay 5 is conductive at times when its anode is positive. The A.C. feed-back to the galvanometer is derived across resistance 35 and applied via transformer 33. The cathode of relay 5 is earthed, thus reducing unwanted pick-up.