Patent GB-596909-A (GB)
Title: Improvements in high-frequency tunable electric circuits
IPC: H03F3/54
Filed: 1944-09-25
Abstract: 596,909. Electric resonators ; valve circuits. GOODALL, M. C., SUTTON, R. W., WRIGHT, C. S., GENERAL ELECTRIC CO., Ltd., BALLANTINE, R. J., and JAMES, E. G. Sept. 25, 1944, Nos. 14229/44 and 24419/45. [Classes 39 (i), 40 (iii) and 40 (v)] [Also in Group XXXVI] The tuned circuit of a short-wave amplifier, mixer or oscillator is of the butterfly type and is divided into two parts of identical construction arranged on opposite sides of a valve, and so connected as to reduce the inductance of the leads and raise the upper limit of frequency. The circuit may comprise a cylindrical shell CD, shown in section in Fig. 4 (14229/44). This shell is symmetrically divided into two halves or loops C, D, which form two inductances connected in parallel. The capacitance is between sets of fixed plates A1 and B1 by way of rotary plates R1 on one side and between A2 and B2 by way of R2 on the other, and is varied for tuning purposes by means of the ganged sets R1, R2 of rotary plates interleaved between the fixed plates. A disc-seal triode is inserted into circular apertures 17, 18 in the sides of the structure, and its anode 12 and grid 11 are connected to plates 13, 14, one or both of which are separated from the structure CD by mica insulation. The cathode 11 is connected to a suitable point of the structure CD through a choke. Thus all the plates in one of the sets such as Al have the same instantaneous potential, instead of a wave distribution of potential, and the electrodes are connected to the resonator by low-impedance paths at 13, 14. In an amplifier, Fig. 7 (14229/44) (not shown), two such structures are joined together, the anode 12 being mounted on one of them as shown in Fig. 4, the cathode on the other, and the grid on a screen which is interposed between them and capacitively coupled to them through mica insulation. The input and output couplings in this case are loop conductors in the space enclosed by the walls C of the respective structures. The two structures may be coupled by placing a metal plate near the open ends of the circuits so as to provide an oscillationgenerator. In a modification, Fig. 6 (24419/45), the two halves of the butterfly resonator, one of which is shown in the corresponding Fig. 5, are mounted coaxially, the axis of the disc-seal triode 9, Fig. 6, being perpendicular to their axis. The arrangement is symmetrical except for the anode connection (which comprises a bracket 24, insulated from but capacitively connected to one of the sets of fixed plates) and the cathode connection (which comprises a spring contact 25 extending over 90 degrees and connected to an opposite set of fixed plates). The edge of the grid disc 11a is in contact with a spring contact 26 which is integral with a shield comprising an upper left-hand part 43 and a lower right-hand part 44, each part extending for 180 degrees round the valve. The spindles 28, 29 of the movable vanes are ganged, and the movable vanes are mounted at the end of each spindle on a boss such as 31, Fig. 5, so shaped that no conductor lies between the vanes, and capacity between them and the valve is thus avoided. The amplifier may be converted into an oscillator by providing a rod which capacitively couples the connections of the grid and anode. In the arrangement shown in Fig. 1 (Comp.), each induction loop comprises a block C1, D1 of square section and having a cylindrical bore, with a gap at 49, 50. The effective capacitances across the gaps are varied by turning a pair of ganged ceramic cylinders 51, 52, each of which carries a metallic layer that is shaped to give the required variation.