GB315821A - Improvements in amplifiers for telegraphic and like signals - Google Patents

Abstract

315,821. Electrical Research Products, Inc., (Assignees of Burton, E. T.). July 19, 1928, [Convention date). Addition to 312,338. Eliminating effects of disturbing currents.-In means for correcting zero wander in cable telegraphy use is made of the effect of magnetic saturation in a transformer with a core of permalloy or like material of high permeability. Signals pass from the input terminals 30 of an amplifier, Fig. 1, to the output circuit 14 through the primary coils 12, 13 of two transformers having permalloy cores. These are biased by coils 17, 18, carrying oppositely-polarizing direct currents. Both cores are saturated in the absence of signals, but the core of the coil 13 is so biassed that it becomes unsaturated for positive signals stronger than the peak strength of normal signals, while the core of the coil 12 is similarly biassed for negative signals. When a positive signal, as a result of zero wander, exceeds the normal peak voltage X as indicated at a, Fig. 2, the core of the coil 13 becomes unsaturated and a pair of impulses B is applied through the secondary 16 to a circuit containing a rectifier. A single negative charge C is therefore stored in the condenser and leaks away as at D, biassing the grid 25 and thus restoring the zero to its normal position. A similar but opposite effect takes place through the coils 12, 15, to correct zero wander arising from negative signals. In a modification a fourth pair of coils applies altermating potential from a local source to the secondaries 15, 16 for the purpose of enhancing the correcting-charge applied to the grid 25, and triode rectifiers are used instead of the rectifiers 20, 26. The circuits in this arrangement may be such that the triode rectifiers have no anode batteries (Fig. 3, not shown) or have separate anode batteries (Fig. 5, not shown). Indicating zero wander. The occurrence and direction of zero wander can be detected by means of the arrangement shown in Fig. 6. The signals pass through primaries 51, 52, the cores of which are oppositely biased by coils 53, 54. So long as the peaks of the signal impulses do not exceed the normal value the cores of the transformers remain saturated, but if this value be exceeded clicks are heard when the telephone 60 is connected at 62 to one or other of the coils 58, 59, according to the polarity of the zero wander.