US2016904A

US2016904A - Electric discharge device

Info

Publication number: US2016904A
Application number: US518152A
Authority: US
Inventors: George F Murphy; Harry C Steiner
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1930-10-08
Filing date: 1931-02-25
Publication date: 1935-10-08
Anticipated expiration: 1952-10-08
Also published as: DE658915C

Description

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i@ 8, 1935., G. F. MURPHY ET AL y ELECTRIC DISCHARGE DEVICE Filed Feb. 25, 1951 Patented Oct. 8, 1935 UNITED STATES PATENT, OFFICE ELECTRIC DISCHARGE DEVICE George F. Murphy, Schenectady, and Harry C.

Steiner, Scotia, N. Y., assignors to General Electric Company, a corporation of New York The present invention relates to electrical discharge apparatus, more particularly to thermionic devices containing an ionizable medium and provided with a source of electrons, a cooperating anode and an electrostatic control member or grid. The pressure of the medium and the impressed voltages are such that a discharge of arc-like character is produced between the electrodes, the initiation of the discharge being controlled by the voltage on the grid. Upon applying the anode voltage, the grid voltage determines whetherl the arc will start 'and by a continued repetition of applying and withdrawing the anode voltage the control member may determine the average plate current over a period of time. Devices of this character' have been described by A. W. Hull in an article entitled Hot cathode thyratrons in the G. E. Review, vol. 32, No. 2, April, 1929, pp. 213-223 inclusive. Such devices find utility where large currents are to be controlled with the application of very small amounts of energy to the grid. Devices of this character often carry considerable current, and in order to provide a sufficient number of electrons with which to produce the necessary ionization, cathodes of large size and weight must be employed. Cathodes of the indirectly heated type are generally used for this purpose on account of their extensive electron emitting surface and high operating eiiiciency. The matter of supporting these heavy cathodes within the envelope presents a diicult problem, particularly where large leading-in conductors of suiicient current carrying capacity are required and these conductors provide the sole support for the cathode. The latter usually is positioned a considerable distance: from the stem in order not to heat the glass unduly, thus necessitating long support leads which may cause a large amount of stress where they emerge from the stem. In certain cases the stems have been known to crack due to vibration or other movement of the cathode swinging at the end of the leading-in conductors. The movement of the cathode is not only undesirable from the standpoint of injury to the stem but also on account of the change in the spacing between the cathode and remaining electrodes which deleteriously affects the operating characteristics of the device.

An object of the present invention is to improve on the supporting structure of a cathode, particularly one of the indirectly heated type to the end that a cathode of large bulk and Weight may be accurately and rigidly positioned Within the envelope. This object is attained in brief by relieving the leading-in conductors entirely of the support of the cathode so that these conductors are called upon only to deliver electrical energy to the cathode. In our improved arrangement, the cathode is carried by arigid me- 5 tallic structure secured to the envelope at a con- Venient place and the conductors are constituted of flexible wire. Another novel feature of our invention is an improved form of end located at the anode stem which stem is characterized by a lo double reentrant portion so as to protect the anode seal from damage due to positive ion bombardment. Other objects and features will be apparent as the specication is perused in connection with the accompanying drawing in 15 which Fig. 1 shows a view in elevation of the improved tube; Fig. 2 is an enlarged View of the cathode shown in Fig. 1 with a portion broken away and exposing the interior members, while Fig. 3 is an enlarged cross sectional view of the 20 anode portion or the envelope.

Referring to Fig. 1, numeral I designates the envelope ofan electric discharge device which terminates in re-entrant stems 2 and 3. The lower stem 3 is closed by a press 4, while theup- 25 per stem 2 carries atthe center a small inverted tubular member 5 open at one end. About midway between the inner end of the stem 2 and the place where it joins the envelope, there is a transverse glass member 6 which carries a piece of 30 tubing l closed at its upper end. 'Ihe member 'I is hermetically sealed to a rigid conductor which passes, rather loosely, through the bore of the tube 5 and is secured to; an anode 9 of any suitable and well known design. The rigid con- 35 ductor 8 is joined to a flexible lead Il! for connection toexternal circuits. The grid or control member takes the form of a perforated cylinder II closed at the lower end and secured in position by embracing the stem 2 to which it is 40 clamped by a metal member I2'. A lead I3 is taken from the grid through a stem I4 which closes the outer end of a transverse glass tubulature I5. In order to improve the starting characteristics of the tube, metallic extensions I6 are 45 afliXed to the lower end of the grid and these extensionscarry a starting ring I'I. The cathode I 8 consists of the usual form of heater (not shown) of which only one of the conductors I9 is illustrated, and about this heater, suitably in- 0 sulated therefrom, are a plurality of rigidly spaced discs 20. These discs are usually coated with an electron emitting material such as barium carbonate (BaCOs) to produce an abundance of electrons necessary for carrying current 55 through the tube. About the discs are located one or more heat shields 2| perforated to allow the egress of electrons `and the ingress of positive ions. The top of these shields is closed by a circular plate 22 which provides a support for one end of the enclosed heater (not shown). The lower end of the cathode is closed by three or more heat shields 20' provided along their periphery with downturned flanges which are secured to the interior surfaces of the respective heat shields 2 I. A cathode of this kind has been described in the Hull application Serial No. 487,- 533, filed October 9, 1930, and entitled Cathode structures for thermionic devices. Also in the Pike application Serial No. 487,541, filed October 9, 1930, and entitled Cathode structures for thermionic. devices. It is evident that the cathode involves a considerable amount of metal and for this reason is quite heavy, particularly in the larger size tubes. In order rigidly to support the cathode within the envelope and in accordance with our invention, we provide a rigid framework 23 consisting of U-shaped metal up'- rights which are secured, preferably by welding, to the surface of the outermost heat shield 2! and at the other end to a resilient band 24 of metal. Three equidistantly arranged uprights are illustrated but it will be understood that the number may vary, depending upon the weight and shape of the cathode to be supported. The member 24 is clamped about the stem 3 and when this member is of suflicient length so as to obtain a large surface of contact with the stem, the framework is held rigidly in place. Intermediate the positions of the cathode and clamp ring 24, there may be secured to the framework 23, two or more shields 25 in order to protect the stem 3 from heat radiated through the lower end of the cathode. The current for the heater is conducted through a flexible multi-strand lead I9 connected to a solid leading-in conductor sealed in the stem 4 and terminating in a ilexible lead 29. The other end (not shown) of the heater is attached to the cap member 22 so that the cathode or load current leads serve as a part of the heater circuit. The load current is taken from the cathode by means of a pair of flexible multi-strand leads 26 connected in parallel, to flattened rigid rods 21 sealed in the stem, also terminating in flexible leads 28 as in the case of the heater circuit.

It is apparent that the heavy cathode structure which may weigh from one pound in the smaller size tubes to ten pounds or even more in the largerI devices, is held rigidly in place by the framework and the strain on the stern is reduced to a minimum by the improved method of support. The fact that the leads. I9 and 26 are flexible, precludes any of the cathode weight from being communicated to the rigid conductors 2T, hence, precludes strain in the glass at the place where the conductors are sealed. It is also evident that the inverted tube 5 prevents the arc discharge from bombarding the place where the conductor 8 is sealed in the stem 'l and to that extent, also precludes puncture or cracking of the glass at this place.

An impro-ved structure of the type described finds particular utility in electrostatically controlled arc discharge devices containing an ionizable medium, such as inert gas or vapor. As stated hereinbefore, the pressure of the latter is such that an arc discharge capable of carrying large currents is produced and the starting of the arc controlled by the inhibiting effect of the grid member IB. Alternating current is usually employed in the plate circuit so as to resto-re to the grid in a` practical manner, the control function at the beginning of each complete cycle. It has been found during operation, that the rigidity of cathode support offered by the framework 23 is such that the cathode is held strictly in proper position notwithstanding a relatively long distance between the latter and the stem which supports it, and the electrical characteristics of the tube as a whole are maintained uniform and reproducible. Moreover, due to the absence of glass strain at both ends of the envelope, the operating life of the tube is materially increased.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. An electric discharge device comprising an envelope winch contains an ionizable medium and which is closed by oppositely directed stems, an anode supported from one stem by means of a rigid leading-in conductor, a cathode supported from the other stem by a rigid framework, a exible lead for the cathode, an extension formed on the anode-supporting stem, said extension terminating in a member which closely surrounds the anode leading-in conductor and extends toward the anode-supporting stem whereby said anode supporting stem is protected from positive ion bombardment.

2. An electric discharge device comprising an envelope terminating in a stem, said envelope containing an ionizable medium and a plurality of electrodes, one o-f said electrodes supported from said ste-m by meansof a conductor, an extension formed on the stem, said extension terminating in a member which surrounds said conductor and extends toward said stem, the electrode to which said conductor is secured being mounted wholly exterior to said extension.

3. An electric discharge device comprising an envelope terminating in a stem, said envelope containing an ionizable medium and a plurality of electrodes including an anode, said anode supported from said stem by means of a conductor, an extension formed on the stem, said extension terminating in a member which surrounds the anode conductor only and extends toward said stem.

4. An electric discharge device comprising an envelope which contains an ionizable medium and which is closed by oppositely directed stems, an anode supported from one stem by means of a conductor, a cathode supported from the other stem, an extension formed on the anode supporting stem., said extension terminating in a member which surrounds the anode conductor and extends away from the anode and cathode.

GEORGE F'. MURPHY. HARRY C. STEINER.