US2054234A - Electric discharge device - Google Patents

Description

Sept. 15, 1936. v. o. ALLEN ELECTRIC DISCHARGE DEVICE Filed July 29, 1933 Ticrl- ATTORNEY Patented Sept. 15, 1936 ELECTRIC DISCHARGE DEVICE Victor 0. Allen, Madison, N. J., assignor to Hygrade Sylvania Corporation, Salem, corporation of Massachusetts Mass... a

Application July 29, 1933, Serial No. 682,760

1 Claim.

This invention relates to electric discharge devices and with particularity to gas or vapor discharge tubes of the grid-controlled type.

The object of the invention is to provide an electric discharge tube of the gas or vapor-filled type which is stable and reliable in operation.

In the gas or vapor tube art, two of the serious drawbacks to uniform operation and stability are the variation of gas or vapor pressure within the tube and uncontrolled ionization, e. g., that caused by primary and/or secondary emission from the control grid and/or the anode. As a consequence such tubes as ordinarily constructed are limited to a relatively restricted temperature range and unless special precautionsare taken to limit the temperature of the gas or vapor within, this range, erratic and non-uniform results are produced. In accordance with the present invention the permissible working temperature range of 'a gas or vapor-filled tube is materially enlarged, rendering the tube reliable and uniform and increasing its operating efiiciency.

Accordingly, one of the important features of this invention resides in a gas or vapor tube of the grid-controlled type, wherein the grid or control electrode is of a material which has a greater heat dissipation than the usual metal electrode, and is substantially entirely free from occluded or entrapped gases.

a vapor or gasefilled tube with a grid or control electrode of a specially prepared synthetic graphite, whereby uncontrolled primary and/or secondary emission is substantially avoided.

Another feature of the invention relates to a gas or vapor-filled tube having a plurality of electrodes of specially prepared synthetic graphite.

A further feature relates to the novel organization, arrangement and relative location of parts which go to make up a more uniform and reliable grid-controlled gas or vapor tube.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed description and the appended claim.

In the drawing, Fig. 1 shows a view, partly in section, of atube embodying features of the invention; and

Fig. 2 shows a modification of the tube of Fig. 1.

Referring more particularly to Fig. l, the numeral l represents any suitable form of enclosing envelope of glass or other similar material. Theenvelope l is provided with a reentrantstem 2 terminating in a press 3 in which are sealed the various lead-in and support wires in a manner well known in the discharge tube art. While the drawing shows one specific manner of mount- .ing the various electrodes, it will be understood that other known types of mounting may be employed.- Centrally supported in the press is an electron-emitting cathode 4 in the form of a coiled ribbon or filament having thereon a coating of emissive material such, for' example, as a mixture of alkaline earth oxides. Preferably,

although not necessarily, the filament is of a nickel-cobalt alloy such as disclosed in copending application Serial No. 667,195, filed April 21, 1933. As shown in the drawing, the filamentary cathode is fastened or welded at its lower end to the support and lead-in wire 5, while at its upper to raise it to emitting temperature. It will be understood, of course, that if desired, the upper I end of the cathode may be supported from a hook or other well-known filament support such as is customarily employed in the radio tube art. Preferably also, the filament coil is of less diameter than the internal diameter of. sleeve 6 so as to eliminate short-circuiting of the filament turns.

It will also be understood that a straight, a V- shaped, or an M-shaped filament may be employed in place of the coil filament shown.

As indicated in the drawing, the sleeve 6 is preferably co-extensive or even greater in length than the cathode and is providedat its upper end with an opening II for the passage of electrons from the "cathode. By this arrangement the emitted electrons are forced to pass towards the anode l2 through the opening H. Surrounding the sleeve 6 is a grid or control electrode l3 which may also be in the form of a sleeve or thimble, preferably of synthetic graphite prepared and treated in accordance with thedisclosure of copending application Serial No. 674,046, filed June 2,1933. Electrode I3 is preferably co-extensive in length with the sleeve 6 and is provided at its upper end with opening Hl in alignment with opening I I. Electrode l 3 is supported in any suitable manner as, for example, by wires l5 and I8 sealed into the press, although if desired, said electrode may be supported from a collar surrounding the-stem 2 as well known in the radio tube art. While the drawing shows'the anode I! in the form of a disc or button supported from the upper end of the envelope I, any other shape and manner of supporting the anodemay be employed.

As stated above, the electrode I3 is preferably of synthetic graphite consisting of artificially graphitized amorphous carbon pressed to the desired shape and subjected to the action of a high frequency electromagnetic field in the presence of an oxidizing gas or agent. This treatment'may be effected prior to the mounting of electrode i3 within the envelope and is continued until all the occluded and/or entrapped gases or carbonaceous products are removed both from the exterior surface, as well as from the bodily interior of the electrode l3, as described in application Serial No. 674,046. As a result of this process the finished electrode is not only entirely free from occluded gases and entrapped carbonaceous products, but also as set forth in said application, substantially all amorphous or non-graphitized material is removed both from the surface and from the interior of the electrode.

It has been found that a tube provided with a synthetic graphite grid as above described is capable of stable operation over a materially greater range of temperature than is possible where ordinary metal mesh or carbon grids are employed. One probable explanation is that the synthetic graphite grid has greater heat dissipation properties than ordinary metal or carbonized metal electrodes, thus allowing the tube to operate at a higher temperature without danger of evolving or freeing occluded or entrapped gases. Because of the special method of treatment above described, the surface as well as the bodily interior of the grid is substantially free from gases or carbonaceous products, thus further reducing the chances of gas being evolved during the operation of the tube. Furthermore, in certain types of vapor tubes employing metal grids, at times the grids become sufliciently hot to act as primary or secondary emitters themselves, which results in uncontrolled ionization. A tube having the specially prepared synthetic graphite grid as described herein, is substantially free from such primary or secondary emission.

and in many cases it is possible to overload the tube appreciably without trouble from primary or secondary grid emission.

If desired, the anode I! may also be made from drop at the cathode surface to a value below the cathode disintegration voltage.

The tube disclosed in Fig. 1 may be utilized with any well-known circuit arrangement for any desired control purpose. For example, the grid i3 may be suitably biased with respect to the cathode 4 so as to control the starting and stopping ofcurrent to the anode II. It will also be understood that the anode i2 may have impressed thereon either a D. C. potential or an A. C. potential. If desired, the opening ll in the grid l3 may be proportioned so as to enable a suitable positive ion sheath to be produced at this opening for control purposes. with this arrangement, therefore, the opening H not only exerts a mechanical and electrostatic action on the electronic flow, but also by reason of the positive ionic sheath exerts an ionic valving action on the electronic fiow. Because of the arrangement of the electrodes shown. any electrons emitted from the cathode must pass through the opening H in order to reach the anode l2, By means of the grid biasing source I! the starting and stopping of the anode current may be regulated.

While the circuit arrangement shown in Fig. 1 shows the tube employed for power control purposes wherein the anode current is controlled by an impulse device It! in the grid cathode circuit,

so as to control the starting and stopping of the anode current, it will be understood that the device may also be used with suitably chosen values of grid bias and anode potential to act as a repeater of electric waves.

Instead of employing a filamentary emitting cathode, the tube of Fig. 1 may be provided with a so-call'ed uni-potential or indirectly heated cathode. Such an arrangement is schematically illustrated in Fig. 2 wherein the cathode i9 is of the type ordinarily employed in so-called indirectly heated cathode radio tubes in which the heating is efiEectuated by means of a filament 20 insulatingly spaced apart from the emitting surface 2l. The remaining electrodes of Fig. 2 may be similar to those of Fig. 1 and further description thereof is not believed necessary.

Various changes and modifications may be made herein without departing from the spirit and scope of the invention.

What I claim is:

In combination an enclosing envelope containing'a filling of an ionizable medium, a thermionic emitting cathode, an anode, a first hollow tubular member of synthetic graphite surrounding said cathode and having an integral conical cap with an opening at one end facing the anode, a second hollow tubular member of synthetic graphite having an integral perforated cap at one end disposed between said opening and said anode, both said tubular members being free from loose carbon particles on their surfaces.

VICTOR O. ALLEN.

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