291,846. Castellain, A. P., and Horton, R. J. March 3, 1927. Vacuum tubes.-In discharge devices such as thermionic valves, the control electrode is partly or wholly within the space bounded by the cathode or within the projection of the cathode on a parallel 'plane or comprises an open frame or solid body with its edges parallel to the limbs of the frame-like cathode. The cathode may lie in channels on the outside of the control electrode. When the cathode comprises two parallel filaments 11, Fig. 1, supported as shown from the pinch 13, the control electrode may comprise either a flat plate 14 between the filaments 11 and twisted to form a support 15 in the pinch or a rod or tube between and parallel to the filaments 11 and secured at its ends to a flat wire spiral around the filaments. An outer control electrode in the form of a flat spiral grid 16 and an anode 18 are provided. When the cathode comprises a hairpin filament, the control electrode may comprise a flat triangular plate 14<1>, Fig. 3, within, and with its edges parallel to, the filament 11; or one or two similar plates 14<11>, Fig. 10, at the side of and parallel to the filament 11 may be used instead of or in addition to the plate 14<1>. The plate 14<1> may be replaced by a wire frame with limbs parallel to and within the filament, the limbs being joined at their lower ends by a cross-wire within or above the pinch and being integral or separate at their other ends. In modifications, the plate 14<1> is replaced by a cylindrical, conical or pyramidal electrode, solid or hollow or formed of spaced wires or of a spiral wire. The plate 14<1> or its equivalents may be crimped, ribbed or corrugated and may have extensions outside or embracing the filament, for example, may carry wire spirals surrounding the filament and secured to the sides of the plate 14<1> or may comprise two plates with edges bent or curved to embrace the filament partially or wholly or may carry annular rings split to allow the introduction of the filament between the rings and the plate &c. When the filament is in the form of an inverted W, the control electrode may comprise a plate with two triangular extensions. In all forms, additional electrodes such as an outer grid and an anode comprising a cylinder or one or more flat plates electrically connected or separate are provided. Two control electrodes may be connected together within the pinch and a resistance may be connected between this connection and the terminal pin or between either control electrode and the pin. The Provisional Specification describes also modifications with N- shaped cathodes and with a flat spiral control electrode within the cathode. Reference has been directed by the Comptroller to Specifications 1694/15, 143,262, 146,357, 150,359, 165,824, 203,962, 219,019, 229,704, 231,225, 247,027, and 248,648.