GB421516A - Improvements in or relating to thermionic valve amplifier and like electrical circuit arrangements - Google Patents

Abstract

421,516. Valve amplifying circuits. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. July 11, 1934, No. 20382. Convention date, July 11, 1933. [Class 40 (v)] Distortion in thermionic amplifiers due to curved operating characteristics is eliminated by injecting into the amplifier input an auxiliary frequency higher than the highest working frequency and of small amplitude compared with the curvature of the characteristic, this amplified control frequency being then utilized to correct the curvilinear distortion. In Fig. 2 the curved characteristic of the valve V is rectified by impressing on the grid an auxiliary frequency from St which is restricted in amplitude in the anode circuit by the network R, C, L1, rectified at G1 and transferred through potentiometer R1 to vary the grid bias of V directly in proportion to the curvilinear distortion produced, and in the opposing sense ; this follows since the amplification of the control frequency will vary with the momentary value of the signal input due to curvature of characteristic. The compensating voltage may be applied to a preceding stage provided that the latter has a straight characteristic ; or the valve to which compensating voltage is fed back may act as a variable resistance across the input of V or in shunt to the load B, or in series with either circuit; alternatively a coupling impedance may be varied. The auxiliary control frequency may be generated by back coupling the anode of the valve to a second grid in the valve V. A compensating system independent of variation in applied control frequency is shown in Fig. 3, S being the network to be corrected, E the signal input, B the output, and St the control frequency. The amplified control frequency is applied through potentiometer P1 rectifier G12 and potentiometer P2 to the outer grid of the control valve SR, the inner grid being fed directly by rectified control frequency. The compensating voltage is derived from the anode resistance RW and applied, as previously described, for correction of S.