US2476940A - Subminiature type vacuum tube structure - Google Patents

Description

July 19, 1949. R. wooo SUBIINIA'I'URB TYPE VACUUM TUBE STRUCTURE Filed lay 22, 1947 Patented July-l9, i949 UNITED v-sunlllnvis'mnr: ma vacuom'mnli' 7 STRUCTURE Boss Wood, East Pepperell, Mesa.

Baytheon Manufacturing Company,

assignor to Newton.

Masai, a corporation of Delaware Application May 22,1947. Serial No. 749,756

This invention relates to electron-discharge de-' vices and more particularly to tubes at the socalled subminiature type. such as are used in p cket radios. hearing aid devices and the like.

The space-saving requirements in devices oi the above general character call for tubes one external dimension of which must be very small, but the other external dimension of which may be somewhat larger. For this purpose, tubes with so-called flat bulbs are used. Such bulbs are of somewhat flattened elliptical shape in transverse cross-section. and have major and minor transverse axes.

It is desirable. from the standpoint or tube electrical characteristics. to have a large spacing between the cathode and the anode of a tube. One of the results of increasing the spacing between the cathode and anode of an electron-discharge tube. is an increase of tube anode resistance, this in turn resulting in an increase of the tube amplification factor.

It is, therefore. one of the objects oi the present invention to increase the cathode-anode inter electrode distance 01 a tube and yet to retain the space-saving advantages obtainable with a flat bulb. 7

Another object is to devise a flat-bulb tube construction which will have a lower control gridanode capacitance than constructions heretofore used.

A further object is to devise a novel suppressorgrid structure for tubes of the flat-bulb type.

A still further object is to utilize the suppressorgrid structure of a flat bulb pentode for supporting the filamentary cathode of the tube, thereby eliminating the need for extra filament-supporting members. thus saving the sp'ace normally required for such members. In tubes of the above general character. a minimum of space is available inside the bulb.

An additional obiect is to devise a'yoke structure for supporting the getter, in a tube of the flat-bulb type. which structure functions also as an electrical connection between the two halves of the anode and furthenas a rigid mechanical connection or fastening between the two anode halves.

the foregoing and other objects oi the invention will be best understood from the following description of an 'exelnplification thereof, reference being had to the accompanying drawing, wherein:

Fig. 1 is a vertical cross-section; on a greatly enlarged scale, through an electron-discharge deviceaccordingto this invention, the electrode as-.

10 Claims. (Cl. 250-275) v 2 sembly being shown in elevation thereof being broken away:

Fig. 2 is a transverse cross-section taken along line s::: of Fig. 1; and

Fig. 3 is a transverse cross-section taken along line 11- 1: oi Fig. l. with the bulb removed.

Referring now to thedrawing, the electron discharge device or tube oi this invention is illustrated as a pentode, and includes an evacuated flat bulls i, of glass or other suitable materl 11, which is of generally elliptical shape in crosssection. therefore having maior and minor transve se axes. or major and minor transverse dimensions. the bulb being somewhat flattened from a true elliptical shape, as shown in Fig. 2. The

' electrode assembly comprises an anode consisting of a pair of similar parallel planar anode elements 2 and 3. a filamentary cathode l. a control or #1 grid 8. a screen or #2 8114 I, and a suppressor or #3 grid consisting oi a pair 01 similarparallel slotted members I and I, said grids all being mounted in the path of the electrons between cathode i and said anode elements 2 and 3. Upper and lower spaced supporting members- 9 and ill, viewing Fig. 1, of insulating material, preferably of mica, provide adequate support and proper spacing for the electrodes. A plurality of resilient projections II are provided, suitably Spaced around the edges of said supporting members. said projections resiliently engaging the interlor walls of bulb I.

Said anode elements I and I, as shown in Fig. 2,

are substantially planar, are-disposed on opposite.

sides of cathode l. and lie in parallel planes. The planet portions of'said elements are rectangular in configuration. Elements I-and I are disposed adjacent the opposite narrow ends of bulb l and lie in planes which are parallel to the minor transverse axis 01' said bulb.

In prior constructions oi the flat-bulb type. the anode halves have lain inplanes which are parallel to the major axis of the bulb, so that the cathode anode interelectrodedistance is measured along the minor transverse aids oi the bulb. By placing the halves oi the anode element according to this invention, that is to say. so that said halves lie in planes parallel to the minor transverse axis of the bulb I. the cathode-anode lnterelectrode distance lies along the major transverse axis oi bulb i, thus enabling such distance to be increased as compared to prior constructions. or made a maximum, while retaining the space-saving advantages obtainable with a very small flat bulb of the type of bulb I. By increasing the cathode-anode interelectrode distance.

andcertainparts The metallic anode elements I and 3 are mounted and supported by the supporting members 9 and HI, and have integral planar tab portions which extend or project beyond members 9 and it, through suitable apertures provided in said members. Between the members and ill, the two vertical side edges of each of the elements 2 and I are bent inwardly at substantially right angles to theplanar or main body portion of each of said elements for a short distance, in order to make said elements more rigid. since said elements are very small.

The maximum possible area of the rectangular planar portion of each of said elements 2 and 3 must be of necessity somewhat smaller than would be possible if the elements lay in planes parallel to the major transverse axis of the bulb, due to the flatness of said bulb, but this is immaterial because, in tubes of the type to which this invention relates, the small amount of plate current does not'cause the problem of plate dissipation to enter.

In order to electrically connect together the two anode halves 2 and 3, a getter yoke I2 is provided at the top of the bulb. This yoke consists of an inverted U-shaped metallic member, in the top horizontally-extending portion of which are two depressions in which the getter compound I3 is placed. The two vertical legs of said yoke are rigidly secured, as by welding, to the corresponding upper tab portions of anode elements 2 and 3. The lower ends of the legs of yoke I! bear on the upper surface of supportin member 9, and, since said yoke is relatively rigid, due to its configuration. said yoke helps to support and maintain in position said elements 2 and 8. Since said yoke is relatively rigid and has a rather high resistance to twisting, it supports the elements 2 and 3 in position during the assembly process, before the bottom of the bulb l is pressed. In addition to providing electrical and mechanical connection between the two anode halves 2 and 3. the yoke 12 supports the getter compound in position. as above described.

Members I and I act as the suppressor grid, as above described, and each of these members is a substantially planar metallic member havin a single slot extending therethrough, each slot havi to the anode halves 2 and I. The planar portions of members I and l are of rectangular shape, as are the slots. Member I is mounted parallel to, adjacent. but spaced from, anode element 2, while member 8 is mounted parallel to. adjacent, but spaced from, anode element 3; therefore, members I and 8 also lie in parallel planes which are parallel to the minor transverse axis of bulb l. Memhers I and I are mounted between cathode 4 and the corresponding anode elements I and 3, so that said members are in the path oi the electrons between said cathode and anode elements. Members I and I are mounted and supported by the supporting members 9 and Ill, and similarly to anode elements 2 and I, have integral planar tab portions which extend or project beyond members 8 and il. through suitable apertures provided in said supporting members. Between said supporting members, the two vertical side edges oi each of the grid members I and I are bent inwardly substantially at right angles to the planar. or

main body portion of each of said elements for a short distance, as shown in Fig. 2. in order to increase the rigidity of said members.

An open-ended trough-shaped or channelshaped metallic member ll hasits base bearing on the upper surface of supportin member 9 and has its right-hand vertical wall rigidly secured, as by welding, to the upwardly-projecting tab portion of member I. Member ll acts as a shield, to reduce or minimize the capacitance between the control grid 5 and the anode element 2; this member also helps to support member I in position. A similar trough-shaped member i5 has its base bearing on the upper surface of member 9 and has its left-hand vertical wall welded to the upwardly-projecting tab portion of member 8. Member it acts as a shield between grid 5 and anode element 3 and also helps to support member 13 in position. These shield members H and I5 need be provided only if the tube is to be used for radio-frequency signals, and may be omitted if the tube is to be used for audio-frequency signals, in which case the upper ends of members I and B may be maintained in position by bending over the upwardly-projecting tabs thereof or by welding a stop member to such tabs above supporting member 9.

The grids 5 and B are wound and supported upon grid side rods lB-IB and l|l1, respectively. These four grid side rods are aligned along the minor transverse axis of the bulb, as shown in Fig. 2, and project through perforations or apertures in the upper supporting member 9 and through correspondingly positioned and spaced perforations or apertures in the lower supporting member Ill. The grids Ii and 8 are of flattened tubular construction. as shown in Fig. 2, and said grids have a common longitudinal axis, the major transverse axes of said grids lying in a common plane which also includes the minor transverse axis of bulb I; the common longitudinal axis of these grids is collinear with the axis of filament 4.

Since the major transverse axes of the grids 5 and 6 lie along the minor transverse axis of the bulb, which bulb axis is very short, there is only a very limited space available for the grids of the tube, since the side rods of the two grids must be spaced not less than a certain minimum distance from each other, for insulating purposes. In a pentode, there must necessarily be three grids, and in the above arrangement of tube elements there is no room for a wound suppressor grid, so that in a flat-bulb construction of the present type the slotted members 1 and 8 described above are used for the #3 grid in place of a wound grid. I

By arranging the elements as above described, with the major transverse axis of control grid 5 and the plane of anode elements 2 and 3 both lying in the direction oi the minor transverse axis of the bulb I, the interelectrode spacing between the said grid and the said anode elements will be measured along the major transverse axis of the bulb. thus enabling said inter-electrode spacin or distance to be increased as compared to prior structures, thereby lowering the grid-plate capacitance in tubes of flat-bulb construction; this is an important advantage of the construction of this invention. l

The filamentary cathode I, which may have an electron-emissive coating thereon, is connected at its upper end to one end of a conducting coil spring I 8, which is coiled around a horizontal support bar IS, the oppositeend of said spring being welded to the upwardly-projecting tab of member I. Support bar it extends substantially parallel to the minor transverse axis of bulb I. and is in turn supported in position by a vertical support rod II. the upper end of which is welded to the rear end or bar it and the lower end of' which is welded to the right-hand vertical wall of shield member I.

A cross plate II is welded to the downwardlyproiecting tab oi slotted grid member I, and one leg or an L-shaped metallic bracket 22 is welded to said cross plate, the opposite leg 01' said bracket extending outwardly from plate II to the right to the longitudinal center-line of bulb I. The lower end of filament l is welded to the upper end of a central lead-in conductor 23. which is in turn welded, near its upper end, to the outwardly-extending leg oi. bracket 22. Thus, the upper end at filament I is secured to grid member I and the lower end to grid member I. Said filamentary cathode 4 passes through two substantially triangular slots 24 and II, respectively, formed, one in the upper and one in the lower supporting member, and by the tension exerted thereon by said spring ll, said filamentary cathode is maintained in the apices of said two triangular slots.

It will be seen, from the above, that the filament l is supported or anchored by the slotted suppressor grid members I and I, thus eliminating the special space-consuming filament supporting members necessary in the prior constructions. In tubes of this type. which may for example have an overall maximum bulb length on the order of 1% inches, a maximum major external dimension on the order of 0.385 inch, and a maximum minor external dimension on the order of 0.285 inch, any design which will save space by eliminating extra supporting members is very advantageous.

A lead-in conductor 2! for the anode elements 2 and 3 is welded to the downwardly-molesting tab of anode element I, a lead-in conductor IT for grid 8 is welded to one of the side rods II or said grid, the rod IT at the right in Fig. 1 for example, a lead-in conductor II for grid I is welded to one of the side rods it of said grid, the rod it at the left in Fig. l for example, and a lead-in conductor is for the upper end of the filament and for grid member I is welded to an enlarged tab 30 in turn welded to the downwardlyprojecting tab of member I. the lead-in conductor 23 being welded to grid member I and the lower end of the filament, as stated above. All of these lead-in conductors are sealed through a fiat press 31 formed externally oi the bulb I at the base of the latter. The electrode assembly is thus retained in place within said bulb l and the required external electrical connections are pro-' vided forthe various electrodes. Leads 21 and 28 maintain grids 6 and I, respectively, in position in the supporting members 9 and ill.

The suppressor grid of a pentode, in order to perform its intended function of reducing secondary-emission efiects, is ordinarily connected to the cathode of the tube. In the device of this invention, it will be seen that both grid members I and II are connected to the cathode I, as desired, but grid member I is connected to the upper end of the cathode, while grid member I is connected to the lower end of the cathode. In other words,

- member I is used as the filament return and member I is connected to the lower end 01' the filament. This means that the two members 7 and 8 will be operated at slightly different potentials, the difierence of potential between said members being the voltage drop in the filament I.

6 However. it has been found that this difierencs of potential makes no appreciable difi'erence in the tube characteristics, both members I and I lunctioning efiectively as suppressor grids.

From the above description, it will be. seen that conductor II is the anode lead, conductor 21 is the screen or #2 grid lead. conductors II and II constitute leads for the filament circuit, and conductor 2| is the control or #1 grid lead.

0! course. it is to be understood that this invention is not limited to the particulardetails as described'above, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. An electron-discharge device, comprising an evacuated bulb, upper and lower spaced supporting members of insulating material inside said bulb, a pair of similar eccentrically-located oppositely-dlspoud metallic electrode members mounted at their upper and lower ends. respectively, in said upper and lower supporting members, said electrode members having integral portions projecting above the upper supporting membar and below the lower supporting member through apertures provided therein, a filamentary cathode passing substantially centrally of said bulb through aligned apertures in said supporting members to points beyond the same, means securing and electrically connecting the upper end of said filament to the upwardly-pro- Jecting portion oi one oi said electrode members. means securing and electrically connecting the lower end of said filament to the downwardlyprojecting portion oi the other of said electrode members, and a pair of anode elements mounted in and between said supporting members, one of said anode elements being positioned on the side opposite from the cathode of each of said electrode members.

2. An electron-discharge device, comprising an evacuated bulb, upper and lower spaced supporting members oi insulating material inside said bulb, a pair of simflar eccentrically-located oppositely-disposed planar metallic electrode members mounted at their upper and lower ends, respectively, in said upper and lower supporting members and lying in parallel planes, said electrode members having integral portions projecting above the upper supporting member and below the lower supporting member through apertures provided therein, a filamentary cathode passing substantially centrally of said bulb through aligned apertures in said supporting members to points beyond the same, means securing and electrically connecting the upper end of said filament to the upwardly-prolecting portion of one of said electrode members, and means securing and electrically connecting the lower end of said filament to the downwardly-projecting portion of the other or said electrode members.

3. An electron-discharge device, comprising an evacuated bulb, upper and lower spaced supporting members of insulating material inside said bulb. a pair of similar eccentrically-located oppositely-disposed metallic grid members mounted at their upper and lower ends, respectively, in said upper and lower supporting members, said grid members having integral portions projecting above the upper supporting member and below the lower supporting member through apertures provided therein, a filamentary cathode passing substantially centrally of said bulb through aligned apertures in said supporting members to points beyond, the same, a pair of similar anode elements mounted inand between said supporting members; one of said anode elements being positioned on the side opposite from the cathode of each of said grid members, each of said grid members having a slot therethrough of a size of the same order as the area of'one of said anode elements, means securing and electrically connecting the upper end of said filament to the upwardly-projecting portion of one of said grid members, and means securing and electrically connecting the lower end of said filament to the downwardly-projecting portion of the other of said grid members.

4. An electron-discharge device, comprising an evacuated bulb, upper and lower spaced supporting members or insulating material inside said bulb, a pair of similar eccentrically-located oppositely-disposed planar metallic electrode members mounted at their upper and lower ends, respectively, in said upper and lower supporting members, said electrode members having integral portions projecting above the upper supporting member and 'below the lower supporting member through apertures provided therein, a filamentary cathode passing substantially centrally of said bulb through aligned apertures in said supporting members to points beyond the same, a pair of similar planar anode elements mounted in and between said supporting members, one of said anode elements being positioned on the side opposite from the cathode of each of said electrode members, said electrode members and said anode elements all lyingin parallel planes, means securing and electrically connecting the upper end of said filament to the upwardly-projecting portion of one of said electrode members, and means securing and electrically connecting the lower end of said filament to the downwardly-projecting portion of the other of said electrode members.

,5. An electron-discharge device, comprising an evacuated bulb, upper and lower spaced supporting members of insulating material inside said bulb, a pair of similar eccentrically-located op positely-disposed planar metallic grid members mounted at their upper and lower ends, respectively, in said upper and lower supporting members, said grid members having integral portions projecting above the upper supporting member and below the lower supporting member through apertures provided therein, a filamentary cathode passing substantially through aligned apertures in said supporting members to points beyond the same, a pair of similar planar anode elements mountedin and between said supporting members, one of said anode elements being positioned on the side opposite from the cathode of each of said grid members, each of said grid members having a slot therethrough of a size of the same order as the area of one or said ing members of insulating material inside said i bulb, a pair of similar eccentrically-locatedoppometallic spectively. in said upper and lower members and lying in parallel planm, said elec- 5 trode members having integral portions projecting above the upper member and below the lower supporting member through apertures provided therein, a filamentary cathode passing substantially centrally oi said bulb through aligned apertures in said supporting members to points beyond the same, means securing and electrically the upp r end 0! said filament to the upwardly-llmiecting portion 0! one of said electrode members. means securing and electrically the lower end of said filament to the upwardly-projecting ing portion of the other or said electrode members, and an anode structure having portions positioned on the sides opposite iron the oathode of each oi said electrode members.

'7. An electron-discharge device, comprising an evacuated bulb, upper and lower spacing supporting members of insulating material inside said bulb, a pair of similar eccentrically-located oppositely-disposed planar metallic electrode members mounted at their upper and lower ends, respectively, in said upper and lower supporting members and lying in parallel planes, said electrode members having integral portions projecting above the upper supporting member and below the lower supporting member through apertures provided therein, a filamentary cathode passing substantially cenh'ally oi said bulb through aligned, apertures in said supporting members to points beyond the same, means securing and electrically the upper end of said filament to the upwardly-projecting portion of one or said electrode members, an angular bracket member securing and connecting the lower end of said t to the downwardly-projecting portion of the other of said electrode members, and an anode structure having portions positioned on the sida opposite from the cathode of each of said electrode mema bers.

8. An election-discharge device, comprising an evacuated envelope, a plurality o1 electrodes supported in said envelope, said electrodes including a filamentary cathode, a pair of grid elements 50 disposed on opposite sides of said filament, a control grid structure disposed between said cathode and said grid elements and an anode structure disposed beyond said grid elements,

said grid elements being insulated from one It another, one end of said cathode being secured and electrically connected to an adjacent portion oi one of said grid elements, the opposite end or said cathode'beins secured and electrically connected to anadjacentportlonottheoflierotsaid 60 grid elements.

9. An electron-discharge device, comprising a iiat evacuated envelope having major and minor transverse axes, an eiectron-emissive cathode supported substantially centrally of said envelope, a substantially planar anode element disposed adjacent a narrow end of said envelope, a grid surroimding said cathode and interposed in the path 0! the electrons between said cathode 70 and anode, said grid having an elongated shape transversetosaidaxeathelongeraxisofsaid shapelyingln a planeparallel to theminorazls oi said envelope, the width of said anode being substantially smaller than the length of said is longer axis of and grid shape, said anode also mm b bersmountedattheiruppcrandlowcrmdam' lying in a plane which is parallel to the minor axis of said envelope.

10. An electron-discharge device, comprising an evacuated envelope, upper and lower spaced supporting members of insulating material inside said envelope, a plurality of electrodes supported in said envelope, said electrodes including a filamentary cathode passing substantially centrally of said envelope through aligned apertures in jecting adjacent portion or one of said arid elements, the opposite end of said cathode being secured and electrically connected to the downweirdly-projecting adiaoent portion oi the other 5 of said grid elements.

ROSS WOOD.

REFERENCES CITED The following referenioes are of record in the said supporting members to points beyond the 10 me of this patent;

UNITED STATES PATENTS Number Name Date 1,913,427 Bond June 13, 1933 i5 2,164,892 Banks July 4, 1939 2,166,744 Seelen et al July 16, 1939 2,355,083 Krim Aug. 8, 1944 2,460,382 Fulton Feb. 1, 1949

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