GB166913A - Improvements in or relating to electric valve or lamp relay and intervalve transformer - Google Patents

Abstract

166,913. Mathieu, G. A. May 3, 1920. Transformers.-Relates to the design of the inter-valve transformers employed in cascade arrangements of thermionic valves, such as shown in Fig. 1. (1) The ratio of transformation is made as high as possible and the coupling as loose as possible subject to the impedance of the transformer primary being equal, when the secondary circuit is in resonance, to the plate-circuit resistance of the preceding valve. Formulµ are given for enabling the constants of the circuits to be adjusted to this condition. The use of high-resistance wire for the transformer windings and of iron cores for high-frequency working) may be avoided, and it is stated that high amplification is obtained together with good stability. (2) When working at high-frequencies it is desirable to reduce as much as possible the capacity between the windings of the transformer. This may be effected by employing a transformer of which one winding' is a solenoid 3, Fig. 3, and the other a series of flat coils 1. It is stated that with this construction a coupling of 25 per cent can be obtained with a capacity of less than 0.0001 microfarad. Or a number of parallel flat coils may be used, of which alternate coils are connected in the primary and secondary circuits. (3) Transformers of the construction shown in Fig. 3 may have one primary and two secondary circuits. One secondary may be connected to the grid circuit of the next valve and the other to a resonance circuit, as shown at the left of Fig. 5, or one circuit may include a retroaction coil, as in the auto-heterodyne detector shown at the right of Fig. 5. This arrangement enables a stepup transformation between the primary 1 and secondary 2 and a step-down between the secondary 3 and the secondary 2, whereby the circuits 1 and 3 may be arranged to induce equal e.m.f.s. in the circuit 2, which is stated to be a condition of maximun sensitivity. (4) For audio-frequency working, iron-core transformers of the type shown in Fig. 7 are used, with a central limb 3 giving large magnetic leakage, so that the coupling may be as loose as desired, while at the same time the primary and secondary circuits have large selfinductance. The grid-filament circuits of the next valve may be connected across only a portion of the secondary winding, as shown in Fig. 7.