GB231972A - Improvements in or relating to thermionic amplifying circuits for telephony - Google Patents

Abstract

231,972. Voigt, P. G. A. H. Jan. 29, 1924. Thermionic amplifiers.-To improve the tone quality of loud speakers &c. associated with valve amplifiers, the speaker S is balanced in a Wheatstone bridge arrangement against a suitable choke coil C (or a similar loud speaker with its diaphragm fixed), and any out-of-balance currents are fed back into the grid circuit of the amplifying valve V. The bridge is completed by resistances or chokes R, and the diagonal AB of the bridge includes the primary coil of a transformer F of which the secondary coil is connected in the grid circuit in series with the input coil D. At frequencies for which the speaker S is resonant, its impedance is less than that of the choke C, and the balance is upset, resulting in a voltage being impressed on the grid circuit by the transformer F in opposition to the original input voltage. The electrical constants of the choke C may be adjusted, or it may be shunted by capacity, so as to accentuate very high and very low frequencies. A transformer T may be interposed between the speaker S and the bridge. The corrected voltages in the plate or grid circuits may be applied to further amplifiers. The transformer F mav be omitted, if the resistances R are replaced by transformer primary coils, the secondaries of which are connected in series in the grid circuit of the valve.