US2973449A - Electric discharge tube - Google Patents

Description

Feb. 28, 1961 M. KUIPERS ElAL ELECTRIC DISCHARGE TUBE Filed Oct. 20, 1958 2 Sheets-Sheet 1 INVENTOR MINNE KUIPERS JAN VAN DER POEL BY wa 1 AGENT Feb. 28, 1961 M. KUIPERS ETAL 2,

ELECTRIC DISCHARGE TUBE Filed Oct. 20, 1958 2 Sheets-Sheet 2 INVENTOR MINNE KUIPERS JAN VAN DER POEL AGE United States Patent 2,973,449 ELECTRIC DISCHARGE TUBE Minne Kuipers and Jan van der Poel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc, New York, N.Y., a corporation of Delaware Filed Oct. 20, 1958, Ser. No. 768,448 Claims priority, application Netherlands Oct. 23, 1957 Claims. (Cl. 313-271) This invention relates to electric discharge tubes having an indirectly-heated cathode, which tubes are suitable for use in circuit arrangements in which a voltage ditference upwards of 1000 volts may occur between the cathode and the filament.

A great difiiculty in such tubes is to provide insulation between the cathode and the filament sufliciently high to avoid breakdown or electrolysis phenomena also in the hot condition.

It is known per se to arrange an insulated helicallywound wire between the filament and the cylinder of the cathode, by which a large portion of the surface of the filament is left free, while nevertheless sufiicient insulation between the filament and the cathode cylinder is retained and the filament cannot shift with respect to the cathode cylinder. However, breakdown is always liable to occur at the points of contact of the insulating layers of the filament wires, supporting winding and cathode cylinder as a result of electrolysis phenomena and the like, while a comparatively great spread in the temperature of different cathodes may occur due to the thermal contact between the said elements inside the cathodes being not always the same.

A very advantageous embodiment is obtained if, according to the invention, the filamentary supporting body consists of bare metal which is secured in the tube quite independently of the cylinder of the cathode. It has been found that, if the filament coated with insulating material is introduced into a helically-wound tungsten or molybdenum wire, the ends of which are secured independently of the cathode, the filament is supported and centered sufliciently rigidly to allow a permissible minimum spacing between the helical winding and the cylinder of the cathode. The supporting body may alternatively consist of a wire netting. If desired, the helical winding or the wire netting may be further stiffened by means of one or more supporting rods which may extend in parallel to the longitudinal axis of the cathode. The supporting body may advantageously consist of molybdenum.

In many cases it has been found possible to use an ordinary grid of suitable size as a supporting body. For example in the case of a cathode of elongated crosssection, the supporting rods may be arranged in the plane of the long axis of this cross-section.

In order that the invention may be readily carried into effect, it will now be described in detail, by way of example, with reference to the accompanying drawing, in which Figs. 1 and 2 show longitudinal sections of two embodiments of a tube having a cathode according to the invention and Fig. 3 shows a cross-section of a cathode as shown in Fig. 2.

Fig. 4 shows another embodiment according to the invention.

In Figs. 1 and 2, reference numeral 1 indicates the bulb of the tube and 2 indicates the base, into which contact pins 3 are sealed. In Fig. 1, a cathode cylinder 4 is supported in mica members 5. Arranged inside the cathode cylinder 4 is a heater 6, which in this case comprises a folded insulated filament 12. The heating element 6 is surrounded by a helically-wound wire 7, which is supported at its ends independently of the cylinder of the cathode, for example by means of supports 8 and 9 which are mounted on the mica members 5. One end of the filament is also connected to the support 9. The Whole is surrounded by an anode 13. In Fig. 2, the cathode cylinder 10 has a barrel-like cross-section as shown in Fig. 3.

The heater 6, which in the case of the embodiment of Figs. 2 and 3 also comprises a folded insulated filament 12, is surrounded by a metal wire 7 wound around two supporting rods 11 in the form of an ordinary grid. In this case also, the extremities of the supporting rods 11 are connected to supports and centered and supported independently of the cathode cylinder 10. As in Fig. 1, these supports are mounted on the mica spacers 5.

The bare metal supporting body 7 thus is spaced along its entire length from the inside surface of the cathode sleeve 10 so as to avoid break-down at the contact points.

In Fig. 4 the supporting body consists of a wire netting 14 Although only three diodes are shown as embodiments, the invention is also applicable to tubes containing one or more further grids between the cathode and the anode.

What is claimed is:

1. An electric discharge device comprising an envelope and within the envelope an indirectly heated cathode assembly capable of withstanding high cathode-filament voltages, said cathode assembly comprising a cathode cylinder, an insulated heating filament within the cathode cylinder, and a bare metal member within said cathode cylinder but completely spaced therefrom and surrounding and engaging and supporting said heating filament substantially along its entire length within the cathode cylinder, said bare metal member comprising a wire of a substance selected from the group consisting of tungsten and molybdenum and helically wound about the filament, and means free of contact with said cathode cylinder and supporting opposite end portions of said metal member within the envelope.

2. A device as set forth in claim 1 wherein a support rod is provided within the cathode cylinder and secured to the helically wound metal member and supporting it within the envelope.

3. An electric discharge device comprising an envelope and within the envelope an indirectly heated cathode assembly capable of withstanding high cathode-filament voltages, said cathode assembly comprising a cathode cylinder, an insulated heating filament within the cathode cylinder, and a bare metal member within said cathode cylinder but completely spaced therefrom and surrounding and engaging and supporting said heating filament substantially along its entire length within the cathode cylinder, insulated spacer means mounted within said envelope, first means supporting said cathode cylinder on the spacer means, second means separate from the first means and free of contact with said cathode cylinder and supporting one end of said metal member on the spacer means, and third means separate from the cathode cylinder and supporting the opposite end of said metal member within the envelope.

4. A device as set forth in claim 3 wherein member is a wire netting.

5. A device as set forth in claim 3 wherein the second means includes plural support rods.

References Cited in the file of this patent UNITED STATES PATENTS the metal 2,367,669 Chevigny Jan. 23, 1945 2,444,483 Wing July 6, 1948 2,870,366 Van Tol J an. 20, 1959

Images