GB344936A - Improvements in or relating to thermionic valve circuits - Google Patents

Abstract

344,936. Valve amplifying circuits. STANDARD TELEPHONES & CABLES, Ltd., SANDEMAN, E. K., and LYALL, J. S., Columbia House, Aldwych, London. -(Reeves, A. H. ; 46, Avenue de Breteuil, Paris.) Dec. 14, 1929, No. 38369. [Class 40 (v).] In resistancecoupled amplifiers of the type in which the plate of one valve is directly connected to the grid of the next, a suitable operating-potential for the grid of each valve is derived from a resistance which carries either anode current or filament current, or both. As shown in Fig. 2, a common plate and grid-biasing battery B is shunted by a potentiometer P, and the earthed filaments are connected to a central tapping. The grid circuit of each valve is completed through a part of the potentiometer which is at a lower potential than the filament, the derived grid-bias being sufficient to offset the direct voltage from the plate of the previous valve. In the modified arrangement shown in Fig. 3, the battery B1 supplies both the filament-heating current and grid-bias. The filaments are fed through a series resistance R4, tappings being taken to each grid from points at suitable negative potentials relatively to the filament. In a third arrangement, grid-bias is derived from a resistance inserted in series between the high- and low-tension batteries. To prevent frequency-discrimination due to the capacity effect of say the valve V2, Fig. 2, across that part Ql of the total potentiometer resistance P1, Q1, a compensating capacity may be shunted across the other resistance element P1.