Abstract: A double-ended thyratron is provided which has, at each end, three grids between a cathode and adjacent voltage withstanding gap, the final grid being connected to its associated cathode. In a circuit arrangement including the thyratron, the first grid adjacent a cathode at each end is connected to a source of current bias and the intermediate grids at each end are connected to mutually isolated trigger signal sources.

Abstract: The invention relates to combustible gas detectors of the kink in which a heatable wire filament exhibits a change in resistance due to a change in its temperature caused by the oxidation of a combustible gas passing over it. In order to avoid poisoning the heatable wire filament is embedded in a pellet consisting of a homogeneous mixture of an oxidation catalyst material and zeolite material the latter preferbly of type X, Y, L or mordenite of large pore size. Additionally layers of catalytically active material and/or inactive non-catalytic porous material may be provided around the outside of the pellet.

Abstract: The invention relates to light biassed camera tube arrangements of the kind in which the light bias source within the overall outline of the tube envelope has one terminal connected to a heater pin in order to provide a source of power. The other terminal of the light bias source is connected to a lead extending to a terminal carried by a protecive end base cap for the tube and a removable disc is provided to fit between the base of the tube and a valve base into which the tube is plugged, the removable disc bearing circuitry and terminals provided to contact selected ones of the terminals carried by the protective end base cap so that the nature of the light bias provided may be selected.

Abstract: In a co-axial multi cavity anode magnetron spurious resonances which would otherwise occur in the space between a magnetic pole piece and an anode shell are suppressed. The resonances may be suppressed by means of short circuit pins located within the anode shell.

Abstract: A display arrangement is provided with two opposite display surfaces so that a display can be seen from both directions. The display arrangement consists of an evacuated envelope and fluorescent screens are provided at both display surfaces which are irradiated by a common electron emissive cathode. This enables a display arrangement to be provided which is very thin, but which is capable of providing very bright displays in an economical manner. Segmented mesh electrodes are positioned adjacent to both fluorescent screens so as to selectively control the regions of the screen which fluoresce, and this enables the nature of the display to be readily altered.

Abstract: A rotatable thermal shutter for use with a pyroelectric camera tube is provided with blades having opening and closing edges in the shape of a spiral. The use of a spiral shape allows the rotatable shutter to have a particularly small diameter while still providing satisfactory performance.

Abstract: A mesh electrode for a c.r.t. display device consists of a number of coplanar portions of mesh insulated from each other, and secured to a support plate by means of two layers of refractory compound. The first layer is applied to the support plate and allowed to set before the second layer is applied so as to space the mesh portions from the support plate by at least the thickness of the first layer.

Abstract: The invention is concerned with monitoring the temperature distribution of a surface which may not be a good emitter of thermal radiation. In the invention a member which is of relatively low thermal conductivity and high thermal emissivity is placed in contact with the surface the temperature distribution of which it is required to monitor so that a thermal image transfers from the latter to the former. A pyroelectric vidicon camera tube then examines the temperature distribution of the member.

Abstract: An addressable display in which data is presented in the form of a rectangular dot array is provided by means of an evacuated cathode ray tube, which enables large bright displays to be achieved. The cathode ray tube contains two segmented mesh electrodes each consisting of separately addressable stripes. Electrons from a flood gun are passed by both electrodes only at the crossing point of two stripes, one on each electrode, when predetermined potentials are applied to them.

Abstract: This invention concerns gas filled thyratrons and is concerned with preventing the formation of arc spots on the grid when the thyratron is operated in a grounded grid mode. The thyratron provided has a grid consisting of three apertured baffle electrodes which are electrically united and occur in sequence in the cathode to anode path of the thyratron. The baffle electrodes on the cathode side of the final baffle electrode forms at least one re-entrant hollow cathode and conductive gauze covered apertures in the baffle electrodes on the cathode side of the final baffle electrode are staggered relative to apertures in the final baffle electrode.

Abstract: The invention provides a thermal camera tube having a reticulated pyroelectric target, that is to say a target having a plurality of separate pyroelectric elements arranged in rows and columns and separated by channels. Each of the separate elements has the shape of a cube the vertical sides of which are inclined so that, except for those in one outer column and one outer row, on two of its sides the top of each element overhangs the base of an adjacent element in the same row and the base on an adjacent element in the same column so that the overhanging surface of the element is exposed to radiation in the region of channels separating it from the aforementioned adjacent elements.

Abstract: A gating circuit intended for use with a camera tube having highlight overload protection is designed to prevent excessively large signals reaching a following video amplifier. These large signals arise when highlight overload protection pulses are applied to the camera tube, and large signals are gated to earth by a pair of diodes arranged to minimize out-of-balance signals.

Abstract: A mesh electrode for a c.r.t. display device consists of a number of coplanar portions of mesh insulated from each other and secured to a support plate by means of a refractory compound incorporating particles larger than the pitch of the mesh. These particles space the mesh away from the support plate and allow the electrode to be easily fabricated.

Abstract: This invention provides an inverter circuit in which an output transformer has a tapped primary winding, one portion of which provides a collector load for a first transistor and the other portion of which provides a collector load for a second transistor, with a saturating transformer arranged to provide oscillatory positive feedback from the collectors to the bases of the transistors. The feedback paths from the saturating transformer to the bases of the transistors each includes the base/emitter path of a respective additional transistor and current is supplied to the collectors of the additional transistors in order to maintain operation during saturation.

Abstract: A travelling wave tube is provided with a slow wave structure consisting of clover leaf cavities in which frequency selective attenuators are present in subsidiary cavities formed within the nose of a clover leaf cavity. Each attenuator consists of dielectric material loaded with attenuation material. The use of the invention enables the coupling properties of the clover leaf cavities and their resonant frequencies to be chosen to provide optimum oscillation suppression.

Abstract: A linear beam tube is provided with a gridded electron gun in which a concave cathode surface is provided with concave channels from which electrons are emitted. The channels may be arranged as concentric annuli. In a preferred embodiment the channels extend radially outwards from the center of the cathode to minimize the effects of temperature distortion. The cathode is provided with a shadow grid and a control grid is spaced from and aligned therewith.

Abstract: A thyratron is provided with a baffled structure between its cathode and first control electrode. The baffled structure consists of a series (e.g. three) annular baffle plates, each having a central aperture aligned with the axis of the cathode, mounted on the end of a cylindrical heat shield surrounding the cathode. The final annular baffle plate, adjacent the first control electrode includes a solid disc within its central aperture.

Abstract: The invention provides a combustible gas detector in which a heatable wire filament embedded in a pellet comprising oxidation catalyst material exhibits a change in resistance occasioned by the change in its temperature which occurs due to the oxidation of a combustible gas passing over it.The pellet is provided with an outer layer of inert non-catalytic material which tends to prevent non-volatile residues from reaching catalytically active regions of the detector.

Abstract: The invention relates to a resonant cavity device such as a magnetron oscillator which is tunable by means of a tuning plunger associated with sealing bellows. A volume defined at least in part by the bellows and producing a range of spurious responses as the tuning plunger is moved is isolated from the resonant cavity or cavities of the device by an isolating choke. The choke may take the form of an annulus having a major radius of 1/4 .lambda. (where .lambda. is the mid-frequency of the tuning range) attached either to the plunger or to the main body of the device and between the bellows and the resonant cavity or cavities.

Abstract: An electronic valve includes a shell electrode which is mounted on a support in such a way as to provide a good continuous electrical contact therewith. The base of the shell electrode is flared and mates with a tapered portion of the support, and is held in contact therewith by means of a clamp.