US2248425A - Rectifier tube - Google Patents

Description

July 8, 1941. w. DQRSEY 2,248,425

RECTIFIER TUBE Filed Feb. 7, 1939 Patented July 8, 1941 ETED STAT QFFICE 2 Claims.

This invention relates to rectifier tubes and particularly to hot cathode gas-filled rectifier tubes for use at high voltages.

An object of the invention is to provide rectifier tubes of simple design and economical construction that may be operated at high voltages without danger of are back, the tubes being characterized by a long leakage path along the glass envelope. Another object is to provide rectifier tubes having relatively large diameter end portions housing the cathode and the anode, and elongated small diameter portions extending between the large end sections. A further object is to provide a rectifier tube in which the glass envelope has a long section of small diameter extending between enlarged end sections that house the cathode and anode, shield rings at the inner and outer surface of the envelope at the region of and electrically connected to the anode, and voltage gradient rings at the inner and outer surfaces of the small diameter section of the envelope.

These and other objects and advantages ofthe invention will be apparent from the following drawing in which:

Fig. 1 is a side elevation, partly in section, of a rectifier tube that constitutes an embodiment of this invention; and

Fig. 2 is a fragmentary side elevation, partly in section, of another embodiment.

In the drawing, the reference numerals l, 2 identify the relatively large diameter end sections of a glass envelope, the end sections merging into and being joined by an elongated smalldiameter section 3. A cathode 4 of known type, for example of nickel coated with barium oxide, is supported by cathode terminal wires 5 that extend through and are sealed in the press 6 within the bulbous end section I. A small quantity of mercury 1 is sealed within the tube to provide an atmosphere of mercury vapor at about 0.01 to 0.04 millimeters of mercury pressure when operating at envelope wall temperatures below 100 C. The mercury is added after the tube has been evacuated and de-gassed in the manner commonly employed in the art.

The anode 8 is preferably a cup-shaped disk of a metal such as pure iron or nickel that will not amalgamate with mercury. The anode is mounted on a stem 9 that extends through and is sealed in the press 10 within the bulbous end 2. The fiat bottom of the anode 8 is normal to the axis of the tube and faces the cathode 4, and the diameter of the anode is no larger, and pref erably slightly smaller, than the diameter of the elongated intermediate section 3 of the envelope. A shield ring II is supported in contact with or closely adjacent the inner surface of the envelope section 2 by wires l2 that are welded to the anode stem 9, and a shield ring l3 may be arranged at the exterior surface opposite the ring 'II and connected to the anode stem 9 by wires l3. The shield ring or rings are located in or adjacent the plane of the flat end of the anode 8.

The length of the intermediate section 3 of the tube will depend upon the operating potentials and, for rectification at 100,000 volts, a length of about 16 inches has proved satisfactory. The dimensions of the bulbous end sections may be the same for tubes of different lengths for operation at different maximum voltages.

The shield ring II is at anode potential and thus broadens out the electric field between the anode 8 and the adjacent end of the envelope section 3. This low electric field intensity is a condition that tends to prevent are back when the anode potential is negative with respect to that of the cathode. The surface charges on the lass walls of the tube play an important part in the rectifier action. The surface charges on the small diameter section 3 probably act as a grid to prevent the development of a high field intensity in the vicinity of the anode.

The function of the outer shield ring I3 is to prevent the development of a high difference of potential radially through the glass wall. This reduces the possibility of a puncttu'e of the envelope wall near the anode. The anode assembly substantially eliminates the erosion or destruction of the anode stem 9 and I have found that it is not necessary to employ the long stem and the accompanying long cylindrical envelope extensions that have been previously proposed.

The small diameter section 3 increases the length of the leakage path along the glass wall from one tube element to the other. Rapid deionization of the mercury vapor in the small diameter section after the current has ceased to flow, tends to prevent are back.

As shown in Fig. 2, one or more sets or rings M, I5 may be arranged in transverse alinement at the inner and outer walls, respectively, of the elongated intermediate section 3 of the envelope. The inner and outer ring of each set may be insulated from each other or, as illustrated, they may be connected by a conducting member l6 passing through and sealed into the glass envelope. These rings establish a definite potential gradient along the envelope and, if desired.

the outer rings I5 may be connected to each other and to the tube elements by resistances or condensers.

Rectifier tubes of the described constructions have been operated satisfactorily at higher potentials than has been possible with prior tubes of approximately the same general type. The tubes do not overheat and external cooling was usually unnecessary. Cooling, if desired, should preferably be at the cathode chamber or end section I.

It is to be understood that the invention is not limited to the particular embodiments herein shown and described, and that many changes may be made in the design of the parts, and in the shape and size of the envelope without departure from the spirit of my invention as set forth in the following claims.

I claim:

1. A rectifier tube of the hot cathode vaporfilled type comprising an elongated envelope, a cathode and an anode at opposite ends of said envelope, and means for establishing a predetermined voltage gradient along the envelope walls between said cathode and anode, said means comprising a pair of conductive rings in transverse alinement and contacting respectively the inner and outer walls of the envelope.

2. A rectifier tube as claimed in claim 1, wherein the end sections of said envelope are of relatively large diameter and joined by an elongated smaller diameter section, and said conductive rings are located at the smaller diameter section of the envelope.

JOHN W. DORSEY.

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