GB731551A - Improvements relating to thermionic valve amplifying and frequency changing circuit arrangements - Google Patents

Abstract

731,551. Valve amplifying circuits; superheterodyne circuits. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. Dec. 4, 1952 [Dec. 4, 1951], No. 30749/52. Classes 40 (5) and 40 (6). A valve is caused to oscillate so strongly that the effective slope is independent of changes in the actual slope. The arrangement may be applied to an amplifier to maintain the gain constant, the valve being back-coupled over a tuned circuit O, Fig. 1, to oscillate at a frequency which is greater than any passed by the signal circuits TE, TA. A further use is in a self-oscillating frequency-changer, to stabilize the damping of the input or output circuits; the Specification describes a number of such arrangements. In one, Fig. 3, local oscillations are generated-in such strength as to render the effective slope constant-by inductive back-coupling between the anode circuit and a tuned grid circuit O. The signal is injected at a null point in circuit O, via a tuned signal circuit E. The arrangement is utilized to stabilize the damping of the I.F. output circuit Z, which is reduced by feed-back via a grid coupling coil RZ. Condenser CE constitutes a by-pass at signal frequencies. The coil RZ may alternatively be included in the cathode circuit. In a modification, Fig. 5 (not shown), the coupling coil RZ is dispensed with and I.F. feed-back obtained by connecting the circuit Z so that a part is also in the grid circuit. The circuit Z is provided with a capacity tap for this purpose, and in a further modification, Fig. 8 (not shown), the oscillator coupling coil RO is connected in series with one of the condensers in question. In another embodiment, Fig. 4, the oscillator circuit O is of the Colpitts type and is connected in series with the I.F. circuit Z, feed-back at I.F. being governed by a tap N which is earthed for such frequencies over the H.F. choke DR. In a modification of this, Fig. 6 (not shown), the oscillator O is connected in the Hartley manner and the tap on the circuit Z is of the capacity type, comprising the anode-to-cathode capacity of the valve, in conjunction with a condenser interposed between the signal input circuit and ground. In still another embodiment, Fig. 9, the input circuit E takes the form of a bridge network, which is balanced by means of condensers T1, T2. The oscillator circuit O is connected to a null point in the circuit E, while I.F. feed-back from the circuit Z is provided for by a capacity tap comprising condensers C1, C2. Specification 729,950 is referred to.