Patent GB-462530-A (GB)
Title: Improvements in or relating to electric circuits for reducing the effective shunt capacity introduced by circuit elements such as, for example, electric batteries
IPC: H03F3/36
Filed: 1935-07-08
Abstract: 462,530. Valve amplifying circuits; impedance networks. BLUMLEIN, A. D. July 8, 1935, Nos. 19480, 25070, and 33805. [Classes 40 (iii) and 40 (v)] The effect of the stray capacity of an element in one circuit to another circuit is reduced by connecting each of the terminals of the element to the points of connection for the element through coupled inductance coils provided with damping means to eliminate the effects of resonance. Fig. 1 shows a direct coupled amplifier in which the effect of the capacity to earth of the battery or other potential source 27 is compensated by the chokes 28, 29, and damping is provided by resistances 30, 32, 34, 35. The chokes are tightly coupled, being wound as a bifilar solenoid or on a common magnetic core and their inductance is made equal to CR<2> where C is the stray capacity 31 and R is the load resistance of the valve, so that the load simulates substantially a pure and constant resistance. In a modulator, Fig. 2 (not shown) a similar coupling is employed between the modulating valve and the modulating resistance. Fig. 4 shows the application to a cathode follower coupling in which the cathode of the valve 37 is coupled to the grid of the valve 50. The inductance of the chokes 28, 29 is made equal to CR<2> where R is the magnitude of resistances 30, 32, and C the capacity to earth of the supply 43 which may be a filament heating transformer. The magnitude of the damping resistances 30, 32 is large compared with the tapped resistances 42, 47. The bias potential for the valve 50 is taken through choke 45 coupled to the chokes 28, 29 to compensate for the effect of the capacity to earth of the bias source 44. In a modification, Fig. 5 (not shown), additional chokes are provided in series in the connections from the source 44 which enables components of more convenient values to be utilized. The chokes may comprise a plurality of separate coils in series each connected in shunt to a damping resistance and are preferably so tightly coupled together that the mutual inductance equals the inductance of the choke. A coupling condenser may be connected between the ends of the chokes remote from the circuit element and a series resistance may be included as auxiliary damping means, and so proportioned that the effective impedance is substantially a pure resistance in the coupling between the anode of one valve to the grid of the following valve. The composite circuit may constitute the whole or part of the load impedance of a valve and in the case where a third inductance coil is employed a further self capacity effect may be compensated and-damping means provided, this circuit serving as the damping means for the primary circuit provided to remove the effect of stray capacity. The first Provisional Specification describes also the use of resistances in place of coupled inductances for connecting a supply source to a direct coupled amplifier or to the electrodes of a cathoderay tube as described in Specification 462,584.