GB499315A - Improvements in or relating to thermionic amplifiers - Google Patents

Abstract

499,315. Valve amplifying circuits. STANDARD TELEPHONES & CABLES, Ltd., JACOBSEN, B. B., and ROCHE, A. H. July 21, 1937, No. 20144. [Class 40 (v)] In a negative feedback amplifier the phase and gain in the feedback path are so modified that instability is prevented whilst leaving the gain substantially unaffected in the operating range. Fig. 1 shows an amplifier of the kind described in Specification 472,256 covering a range of 12 ... 60 kc., and in Fig. 3 the curve Á shows the phase shift, f1, f2 being the limits of the operating range without correction. The phase shift may be corrected at the ends of the range by inductance L1 shunted by resistance R4 and condenser C2 shunted by resistance R2 to obtain a curve #, Fig. 3. A bridge type of feedback for both input and output may be used, Fig. 6 (not shown), while Figs. 8, 8a show modified phase correcting networks which may be used in the feedback circuit when a phase shift of more than 90‹ is required to give a curve #2, Fig. 3. A band elimination filter may be incorporated in the feedback path and a plurality of feedback paths may be used which may include the input and output transformer. With two feedback paths, the corrective networks may be divided so that one path corrects the upper, and the other path the lower end of the frequency scale.