GB720805A - Electrometer amplifier - Google Patents

Abstract

720,805. Valve amplifying circuits. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET. March 12, 1953 [March 14, 1952], No. 6794/53. Class 40 (6). An electrometer amplifier comprises four valve stages direct-coupled in cascade and with overall negative feed-back, provided by means of a resistor 17 common to the cathode circuits of the first and last stages 10, 33. The first stage 10 has a series grid resistor 11 and is operated at low heater and anode voltage and anode current. The grids of the second and third stages 22, 30 respectively, are directcoupled to the anodes of the corresponding preceding stages 10, 22. The anode load resistors 21, 24 are returned to the cathode 29 of the third stage, to which the grid of the final stage 33 is also coupled, via a potentiometer 34, 35. The lower end of the potentiometer 34, 35 connects to a source of negative bias comprising mains transformer 6, rectifier 8 and smoothing condenser 9. The cathode 25 of the second stage may be connected to a potentiometer 27, 28 between the cathodes 16, 29 of the first and third stages. Alternatively, Fig. 3 (not shown), it may be connected directly to the cathode 16 of the first stage, in which case the grid 22 is taken to a potentiometer between the anode of the preceding stage and the bias source 6, 8, 9.