US1733504A

US1733504A - Vacuum tube

Info

Publication number: US1733504A
Application number: US42757A
Authority: US
Inventors: William A Macdonald
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1925-07-10
Filing date: 1925-07-10
Publication date: 1929-10-29
Anticipated expiration: 1946-10-29

Description

Patented Oct 29, 1929 UNITED STATES PATENT OFFICE WILLIAM A,.MACDONALD, OF LITTLE NECK, NEW YORK, ASSIGNOR TO HAZELTINE CORPORATION, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF DELAWARE VACUUM TUBE Application flled July 10,

This invention relates to vacuum tubes, more particularly to the structure of thermi onic vacuum tubes having two or more lnternal elements or electrodes, and has for its object the provision of structural features which effect extreme rigidity of the elements, economy in manufacture, and certain other improvements hereinafter to be described.

The rigidity of the elements of vacuum tubes has become of increasing importance as the various apparatus to be used therewith have been developed to be more efficient and critical. For many reasons a long cathode element or filament electrode is desirable, and there has been especial dilficulty in supporting this element so that it will not sag or change its position relative to the other elements. It has been the practice to utilize a glass press for supporting the individual elements through the medium of a number of supporting wires which may besuitably bent to align and space the elements. These wires, after passing through a glass press, are likewise employed to make external connections to theelements of the tube. After the tube is assembled, a mechanical shock or blow will often bend the supporting wires and materially change the tube characteristics, or even bring the elements into electrical contact. Such means of element support also allows of objectionable vibration of the elements which results in what is commonly called microphonic action.

With a view toward increased rigidity, it has been suggested to clamp the plate electrode securely to the glass stem below the press, and to locate and space the grid and filament electrodes by means of insulating blocks attached to the extremities of the plate. This method appears to provide more rigidity than the former method, but is not so generally used because of greater manufacturing cost. In addition, it will be noted that neither method provides any means for supporting the filament rigidly throughout its length. The present invention I provides simple means for rigidly supporting the filament and concurrently provides means for supportingand spacing the other elements wlthin small 1925. Serial No. 42,757.

Fig. 2 illustrates two electrode-spacing caps secured in place on the filament-supporting mandrel;

Fig. 3 isan end view of the assembly of .Fig. 2;

Fig. 4 shows the completely assembled electrode unit;

of Fig. 4 as supported above the press of a vacuum tube;

Fig. 6 is a front view of a complete vacuum tube including the elements assembled, mounted and supported according to the invention; and a \v Fig. 7 is a cross-section of an alternative form of mandrel.

Referring now to Fig. 1, it will be seen that a filament electrode or cathode element 1 is wound in a helix around a mandrel of refractory material such as soapstone or Pyrex glass. The filament, which frequently is long and fragile, is thus supported throughout its entire length byv the mandrel. According to a preferred construction, the mandrel extends a short distance at each end beyondthe filament so that electrode-spacing caps 4 maybe secured over the end of the mandrel, as indicated in Figs. 1 and 2. A wire 3, larger and stronger than the filament and which may Fig. 5 shows the completely assembled unit preferably be of nickel, is molded or otherwise inserted into the mandrel at each end thereof, and serves both to connect the filament to the external circuit and to support the electrode assembly. In a vacuum tube of small size, one such wire in each end of the mandrel will usually prove sufficient; although if the completed assembly be somewhat heavier, a larger wire than shown, or

, low electrical resistance, and consequently a considerable length of filament wire must be employed in order that the filament may be heated by an electric source at conveniently high potential and with an economically low current. In addition, platinum is to a large extent chemically inert, and may be successfully coated with electron-emitting substances.

-An enlarged cross-section of an alternative supporting mandrel is shown in Fig. 2. It is not always desirable to employ a supporting mandrel which touches the filament throughout its length, and therefore a fluted mandrel or one of polygonal cross-section,

. having a number of projections or edges which support the filament substantially by point contact so that the heat from the filament will not be conducted'away through the solid material of the mandrel, may be desirable. It should be noted, however, that a mandrel of circular cross-section, as shown in Figs. 1 and 1, need not necessarily conduct away as much heat from the filament as would at first be supposed, because it is customary to coat the filament with an earthmetal oxide or other electron-emitting material to increase the natural electron emission of the cathode, and this oxide, or other coating, usually possesses the property of low heat conduction. If this substance does not possess that property, then a coating of'a substance which does possess low heat conductivity may be applied to the mandrel. It has been found expedient first to coat the mandrel with such oxide or other substance, subsequently to wind the filament thereon, and then to apply more coating material to the filament and mandrel, thus embedding the filament in an oxide or other coating.

The third step in the process of assembly would normally be'to mount the spacing or end caps 4 over the ends of the mandrel as shown in Fig. '2. These caps may be of a refractory and insulating material similar to that used in the mandrel, or may be of a different material, but should be formed accurately, because it is the dimensions of these 1 caps which determine the spacing of the electrodes. It is usually preferable to manufacture the spacing caps separately from the mandrel in order that the. dimenslons may be accurately determined, although, of course, if

the tubes are to be manufactured in large,

quantit utilized to form the mandrel and spacing caps in one integral piece. During such molding process the comparatively low resistance lead-in wire 3 may also be molded in place.

-If the latter molding process is employed, the next operation of assembly would be the placing of a grid electrode 8 upon shoulders 6 (Fig.2) of the end spacing caps as indicated in Fig. 4. This electrode may be of wire mesh, perforated metal, or of other suitable construction. If the grid electrode be 4 made in tubular form, it would, of course, be necessary to place it over the mandrel before the second end cap is put in place. A slot 10 is shown in Fig. 3 through which is brought the lead-in wire connected to the grid. The last operation in the electrode assembly is the placing of the plate electrode or anode 9 (Fig. 4) over the outer shoulders 7 of the spacing caps.

In the embodiment illustrated the plate electrode is of circular cross-section. It should be noted, however, that while, for convenience in manufacture, electrodes of circular cross-section are desirable, electrodes of other cross-section, such, for instance, as that shown in Fig. 7, may be utilized to advantage. I

In Fig. 5 the completed electrode assembly a molding process may readily be,

is shown mounted and supported above the glass press 12, through which the connecting leads pass. Rigid supporting wires 11, which may also carry the filament current, are

shown extending from each end of the elec-.

trode assembly and are preferably spot-welded to the filament lead-in wires 3. It is in many instances desirable to make lead-in wires 3 of a len th and rigidity suflicient totake the place of supporting wires 11, and to anchor the same directly in the glass press 12.

The illustrations of the embodiment described show the elect-rode assembly as being mounted horizontally in the glass envelope or bulb 13, Fig. 6; but, because of the unusually stable characteristics aiforded by this invention, the assembly may be mounted vertically,

or in any convenient position, since the operating efiiciency is in no way influenced thereby. In order to conserve space and to expedite evacuation, the assembly illustrated "III in Fig. 4 may conveniently be mounted in a glass tube slightly larger than the diameter of plate 9, and two lead wires brought out from each end, thus eliminatng the large base 14 shown in Fig. 6,'together with the increased effective inter-electrode capacity resulting therefrom.

The construction as illustrated and described above permits of very rapid assembly by comparatively unskilled labor with the assurance of a standardized product of unvarying characteristics. As will at once be observed, the plate-grid spacing isdependent entirely upon the dimensions of the spacsively by said end caps,

ing caps 4, which may be cheaply manufactured with great accuracy. he electrode assembly is in itself extremely rigid, and is not affected in any way by vibration or mechanical shocks within reasonable limits. This rigidity is due to the unusually solid support of the various electrodes, by reason of the fact that the filament is su ported throughout its entire length, and tiie grid and plate electrodes are supported on both ends around their entire perlmeters. The assembly being in one complete unit, any shocks to WhlCh it may be subjected will affect all of the electrodes simultaneously, and there will be substantially no movement of any one electrode relative to the others.

I claim:

1. A vacuum tube electrode structure comprising a mandrel of refractory insulating material, a cathode comprising1 a filament supported substantially throu out its entire length by said mandrel, ouble shoulders of insulating material at each end of said mandrel, a control electrode su ported at both ends by a pair of said shoul ers, an anode supported at both ends by the other pair of saidshoulders, and means partially embedded in said mandrel for supporting said structure from both ends thereof within an evacuated envelope.

2. A vacuum tube assembly including a cathode structure which comprises a man rel of insulating material coated with an electron-emitting substance, a filament coiled around said mandrel, and an additional coating of said electron-emitting substance embedding said filament, end caps for said mandrel having spacing shoulders thereon, a tubular control electrode supported and spaced from said filament electrode exclua tubular plate electrode supported and spaced from said control electrode exclusively by said end caps, means for making externa connections to said electrodes, and means including at least part of said connecting means for supportin the electrode assembly within an evacuate envelope.

3. A vacuum tube comprising an elongated mandrel of refractory non-conducting material, a filament wound helically around said mandrel and rigidly supported thereby for substantially its entire length, a pair of caps of refractory non-conducting material attache'd to opposite ends of said mandrel, each of said caps having a pair of shoulders, a cylindrical control-electrode element supported at its ends by said caps, each end of said-=control electrode element being properly positioned by one of the shoulders on its supporting cap, a cylindrical anode element supported at its ends by said caps, each end of said anode element being properly positioned by the other shoulder on its supporting cap, said mandrel, caps, filament,

' ported control-electrode element and anode element being combined into a unitary self-contained structure, said self-contained structure being supported exclusively by means connected to the ends of said mandrel, said filament, control-electrode element and anode element being separated except at their ends by evacuated space, and an evacuated envelope enclosirig said unitary structure.

4. vacuum tube comprising an elongated mandrel of refractory non-conducting material, a filament wound helically around said mandrel and embedded in a coating of electron-emitting oxide, said filament being rigidly secured to said mandrel for substantially its entire length by means of said oxide coating, a pair of annular caps of refractory non-conducting material attached to opposite ends of said mandrel, each of said caps having a pair of concentric circular shoulders, a cylindrical control-electrode element supat its ends by said caps and enveloping said filament, each end of said controlelectrode element being properly positioned by one of the shoulders on its supporting cap, a cylindrical anode element supported at its ends by said caps and enveloping said control-electrode element, each end of said anode element being properly positioned by the other shouler on its supporting cap, said mandrel, caps, filament, control-electrode and anode element being combined into a unitary self-contained structure, said unitary structure being supported exclusively by means connected to the ends of said mandrel, said filament, control-electrode element and anode element bein separated except at their ends by evacuate space, and an ev'acuated envelope enclosing said unitary structure.

5. A vacuum tube assembly including a cathode structure comprising a mandrel of refractory insulating material coated with a substance of low specific heat conduction, a heating filament wound around said mandrel and su ported substantially throughout its entire ength thereby, an electron emitting substance coating said filament, double shoulders of insulating material at both ends of said mandrel, a control electrode supported at both ends by a pair of said shoulders, an anode supported at both ends by the other pair of said'shoulders,

edded in said mandrel for supporting said structure from both ends thereof within evacuated envelope, and means for cdnd cting a heating current to and from said filament.

In testimony whereof I aflix my signature.

WILLIAM A. MACDONALD.

means partially im-