GB684909A - Improvements in or relating to circuit arrangements comprising a plurality of amplifiers - Google Patents

Abstract

684,909. Valve amplifying circuits. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Oct. 12, 1951 [Oct. 17, 1950], No. 23824/51. Class 40 (vi). In an arrangement employing a number of amplifiers in parallel, in which the output of each is stabilised by means of a negative parallel feed-back operative over a biased rectifier, the input circuit of each amplifier includes an impedance inverting network. By this means the input impedance increases as the negative feed-back path becomes operative, and prevents loading the common source as would otherwise occur. A carrier applied over transformer 11, Fig. 4, to a valve 10 is fed out through transformer 12 to a load and over winding 17 to a rectifier 13 biased by battery 14. When the output is sufficiently great the rectifier conducts and applies feed-back to the grid of the valve 10. Inductor 19 and capacitor 20 act as an impedance converting arrangement so that the decrease in impedance due to the feed-back is caused to appear as an increase in the load impedance presented to the input source. In a modification, Fig. 5, two inductors 21, 22 and two capacitors 23, 24 are used. In a further modification, Fig. 6 (not shown), the input transformer is centre-tapped and connected to one input lead, the other being connected through a capacitor to one end of the primary and through an inductor to the other end. The winding 17 may be on a current transformer, Fig. 7 (not shown), when it is desired to maintain the output current constant. A push-pull arrangement is also described, Fig. 8 (not shown).