Abstract: Method of providing a pattern of apertures and/or cavities in a plate of material which is suitable for powder blasting, or of cutting pieces from a plate (2) of such a material by means of powder blasting, using a non-metal layer of blast-resistant material (3) as a mask which is patterned while or after it is fixedly provided on the surface of the plate.

Abstract: After a plate of electrically insulating, particularly hard and brittle material has been provided with a mask having a very large number of patterned apertures, it is exposed to at least one jet of abrasive powder particles, which jet is moved relative to the plate. In this way a plate is manufactured with a pattern of apertures and/or cavities which are eminently suitable for manipulating electron currents in electronic displays. Plates manufactured in this way may be used, for example, as control plates, spacer plates, or electron transport duct plates in electronic displays.

Abstract: A method of providing a plurality of cavities and/or apertures in a plate or layer wherein, after the plate or layer has been provided with a mask having a plurality of apertures arranged in a pattern, at least one jet of abrasive powder particles is moved relative to the plate. On its exposed surface, the mask is provided with a coating which prevents substantial mechanical stresses from being generated in the mask during the process by the jet of powder particles.

Abstract: After a plate of electrically insulating, particularly hard and brittle material has been provided with a mask having a very large number of patterned apertures, it is exposed to at least one jet of abrasive powder particles, which jet is moved relative to the plate. In this way a plate is manufactured with a pattern of apertures and/or cavities which are eminently suitable for manipulating electron currents in electronic displays. Plates manufactured in this way may be used, for example, as control plates, spacer plates, or electron transport duct plates in electronic displays.

Abstract: A method of providing a plurality of cavities and/or apertures in a plate or layer wherein, after the plate or layer has been provided with a mask having a plurality of apertures arranged in a pattern, at least one jet of abrasive powder particles is moved relative to the plate. On its exposed surface, the mask is provided with a coating which prevents substantial mechanical stresses from being generated in the mask during the process by the jet of powder particles.

Abstract: An electrodynamic loudspeaker (1) has a diaphragm comprising a central part (2) and a peripheral part (3), and a voice-coil device (9, 10) coupled to the central part (2). The surface ratio S.sub.2 /S.sub.1 complies with the relationship 0.5.ltoreq.S.sub.2 /S.sub.1 .ltoreq.6, where S.sub.1 and S.sub.2 are the surface areas of the central part (2) and the peripheral part (3) respectively. The mass ratio m.sub.2 /m.sub.1 complies with the relationship 0.5.ltoreq.m.sub.2 /m.sub.1 .ltoreq.8 where m.sub.1 and m.sub.2 are the mass of the central part (2) and the voice-coil device (9, 10) and the mass of the peripheral part (3) respectively. Further, the stiffness imposed on the diaphragm by the space (6, 6') defined by the diaphragm (2, 3) and the chassis (4) and/or the magnet system (7) is smaller than the stiffness of the diaphragm itself. Thus it is possible to derive a car loudspeaker which has a specific dip in its frequency response characteristic P (FIG. 2a), measured in an anechoic room.

Abstract: An electron gun for a camera tube includes an anode and a cathode. The cathode is assembled in a cathode support which can very readily be adjusted relative to the anode in the non-connected condition. In particular, the cathode support and the anode are movable radially with respect to each other and with respect to an axis. An emissive cathode surface and a part of the anode extending perpendicular to the axis remain accurately parallel to each other during the radial movement. As a result of this it is possible to cause the central path of the generated electron beam and the gun axis to coincide so that extra correction coils for aligning the electron beam may be omitted.

Abstract: An electron gun for a camera tube includes an anode and a cathode. The cathode is assembled in a cathode support which can very readily be adjusted relative to the anode in the nonconnected condition. In particular, the cathode support and the anode are movable radially with respect to each other and with respect to an axis. An emissive cathode surface and a part of the anode extending perpendicular to the axis remain accurately parallel to each other during the radial movement. As a result of this it is possible to cause the central path of the generated electron beam and the gun axis to coincide so that extra correction coils for aligning the electron beam may be omitted.

Abstract: Disclosed is a bayonet catch for directly securing an electrode in a glass envelope which comprises projections extending inwardly from the envelope and radially extending portions on the electrode which are clamped between the projections upon rotation of the electrode. The material of the envelope and the electrode have substantially equal coefficients of expansion to minimize relative movement between the envelope and the electrode with changes in temperature.