288,663. Robinson, J. Nov. 30, 1926. Vacuum tubes.-The envelope of a thermionic valve having a cathode, one or more anodes and one or more grids contains also juxtaposed elements similar to the anode and grid but functioning solely as a condenser. One element, but not both, may be an extension of, or directly connected to, the anode or grid, such connection being the only permanent connection within the valve between the elements and any of the valve electrodes. The cathode is asymmetrically arranged with respect to the electrodes and elements so that the elements are outside the cathode field due to their positioning and not to screening, there being little or no flow of electrons to the elements. The condenser formed by the elements has a capacity and high-frequency reactance of the same order as, or, if the elements are physical duplicates of the anode and grid, equal to, those of the condenser formed by the grid and anode. The anode A, Fig. 5, may be insulated from an element A<1> similar to it, a grid G extending along both the parts A, A<1> and the cathode extending along the anode A only so that the element A<1> and the part of the grid near it form a condenser. In modifications, the grid G may be divided at its centre instead of or in addition to the division between the parts A, A<1>; a further grid may be arranged between the grid and anode; the divisions of the grid and anode may be unequal; the anode parts may be spiral each with a terminal at one or both ends; and element A<1> may be arranged non-axial to the anode A at one side thereof and may then contain a grid element connected to the grid G. More than one of such special valves may be arranged in one container with their filaments in series or parallel; two such valves and one rectifier valve may be mounted within one envelope. The valve may be used in radio transmission or reception and for high or low frequency amplification. An anode inductance A, Fig. 7, may be joined between the anode A and the element A<1> and tuned by a condenser C, the high-tension battery being connected to a central or variable tapping point and successive valves being inductively or capacitively coupled. When the anode is undivided and the grid divided, the parts of the grid may be connected across an inductance with a tapping connected to the filament through a battery or potentiometer. Three high-frequency amplifiers may be followed by a detector with reaction, a neutralizing effect being produced to prevent radiation. The Provisional Specification describes valves in which both parts of a divided anode are in the cathode field and function as electrodes, in which the anode is divided on a plane containing its axis, in which the anode inductance is connected at one end directly to an anode part and at the other end, through a resistance and condenser in parallel, to the other anode part, in which one anode part has no grid between it and the filament and is close thereto, and in which an additional anode is used to obtain a current varying with the filament emission and so to compensate for varying emission by compensating the main anode current or by varying the potential of the main grid to keep the main anode current constant.