US2751517A - Filament structure for electron tube - Google Patents

Description

June 19, 1956 H. D. DOOLITTLE FILAMENT STRUCTURE. FOR ELECTRON TUBE Filed Nov. 1, 1951 INVENTOR HOWARD D. DO

@TTLE ATTORY United States Patent T FILAMENT STRUCTURE FOR ELECTRON TUBE Howard D. Doolittle, Stamford, Conn., assignor to Machlett Laboratories, Incorporated, Springdale, Cnn., a corporation of Connecticut Application November 1, 1951, Serial No. 254,371

4 Claims. (Cl. 313-265) This invention relates to an electron tube structure which is to be subject to shock and vibration. In particular, it concerns a means of preventing filament breakage in such a structure.

Mechanical shocks and vibrations are frequently experienced by electron tubes. Rough handling during shipment is a primary cause of mechanical damage to tubes. Furthermore, many uses for vacuum tubes require them to be mounted in locations where mechanical vibrations frequently occur. These mechanical shocks and vibrations are transmitted to the various tube elements thereby causing them to vibrate. The amplitude of vibration of the electrode in many instances, however, is small due to their secure mounting. In particular, elements solidly supported at both ends have relatively little opportunity to vibrate. On the other hand, where one end of an element is not securely fastened in place, the amplitude of vibration may become large. For instance, the vibration of free-hung filaments may sometimes reach an amplitude which exceeds the grid-filament spacing. Thus, vibrations imparted to such a filament are apt to produce contact between the grid and filament which, if a sharp impact, may cause the filament to shat ter. The tendency to shatter is particularly serious with filaments which are constructed of brittle material such as 'thoriated tungsten. Furthermore, such contact or shorting is particularly undesirable during tube operation as it may upset the mode of operation.

There are a number of factors which determine the possible amplitude of vibration of a vacuum tube element. Of significance is the rigidity of that element and its support. In a stranded filament, the diameter of each strand, the length of the strands, and the number of strands will each, in part, determine the rigidity of the filament.

Other elements may be made with component parts suf-' ficiently sturdy to avoid large vibrational movement, but I the cross section of the filament strands, as well as the 0 number of strands and the lengths of strand, is limited by the resistance required for heating the filament and other design factors. As a consequence, the relatively flimsy filament structure has both a larger amplitude of vibration and a greater tendency to shatter upon striking an adjacent electrode. Obviously the hazard of shorting and breakage is increased if the grid and other elements as well as the filament are constructed so that they have a large amplitude of vibration.

In the prior art a number of means have been devised for minimizing the opportunity of filament breakage. Often these means consist of some object between the filament and the grid which will limit the opportunity for vibration. Usually such a means is affixed to the filament 2,751,517 Patented June 19, 1956 ice in such a way that it will strike the grid or other adjacent electrode before the filament itself is able to strike it. Even though this means is insulated from the filament so as to prevent shorting between the filament and the grid,

its use adds weight to and complicates the filament strucdiameter and which is placed within the filament. This.

bumper is attached to a center mast which does not touch the filament structure itself, but which may advantageously be solidly afiixed to the filament mounting.

My invention. avoids putting into the interelectrode spacing between the filament and the grid any object.

which might upset tube characteristics or cause shorting of those two elements.

upon an active tube element. normally must rely upon support from one of two electrodes between which it lies. Thus such an interelectrode member adds to the structural load of the supporting electrode and lowers that electrodes resonant frequency tova point where it is more apt to resonate from a shock,

thus to a large degree defeating the purpose of the interelectrode member. Furthermore, the use of such a mer n' ber complicates the electrode structure in a way which might alter the electrical characteristics of the tube in an undesirable manner. member in the interelectrode space will add to the inter-.. electrode capacitance.

My invention is also advantageous in that it employs a,

stationary bumper for mechanically damping vibrations.

By placing the bumper atop a sturdy center mast mounted on the filament support, the position of the bumper is:

fixed relative to this support and other relatively fixed parts of the tube. Thus vibration, relative to the support is discouraged and the amplitude of vibration is limited to approximately that which would be possible were the free end of the filament fixed relative to the support.

This limitation on the amplitude of vibration is accom-' plished without end cooling and the other undesirable.

consequences of solidly mounting the free end, as by means of a center mast.

For a better understanding of my invention reference is made to the following drawings:

Fig. 1 illustrates in section an electron tube my invention.

Fig. 2 shows in perspective the bumper member andv the filament support structure.

Referring to Fig. 1, the electron tube shown employs a glass envelope having an enlarged portion 10 which At one end of contains the active elements of the tube. the envelope a narrow neck 11 has sealed to it cup 12,

whose lip is advantageously kovar or other glass sealing metal. Cup 12 advantageously has a reduced diameter portion 12a which snugly accommodates enlarged. cylin} 1: drical portion 13, which is mounted at one end ofelon. gated anode support 14. The anode itself 15 is tubular in shape. That end of the anode adjacent its support is closed by cap 16. Wire-like support members 17 are Likewise, my invention avoids the necessity for supporting such an interelectrode means- An interelectrode member It is inevitable, of course, that a employing tabs 40a.

'Joseph W. Skehan, Serial No. 254,330, filed November 1, 1951, now Pat. No. 2,681,422.-

A narrow neck in the side wall of envelope 10 is sealed to the lip of cup 21. Cup 21 advantageously has a reduced diameter portion 21a which accommodates the enlarged ball-like end portion 22 of elongated grid support member 23. This construction, which is also described and claimed in the above mentioned copending application Serial No. 254,330 of Joseph W. Skehan, is desirable in that it permits universal adjustment of the grid during the positioning thereof. Support member 23 has its end opposite enlarged portion .22 bent in such a way that'it may be conveniently afiixed to ring 24. Ring 24 is the support ring for grid 25 which, in this instance, is a structure composed of parallel wires held in place by a helical winding.

An enlarged neck 27 of the envelope, oppositethe anode neck 11, has a re-entrant portion 28 which is terminated in stem press 29. An exhaust tubulation 30 is advantageously located within the re-entrant portion of the neck and ported through the stem press 29. Rod-like metallic conductors 31 and 32 are sealed through the stem press and connected outside of the tube envelope to filament leads 33 and 34. Within the tube envelope conductor 32 is joined by strip conductor 35 to axial rod-like conductor 36'which has one end embedded within and supported by the stem press. The filament is advantageously a freehung structurei. e., parallel strands circularly arranged with convergent portions near one end fixed together.

The filament support structure is more readily seen in Fig. 2. Basically, it consists of the coaxial tubular members. The inner tubular member 38 advantageously fits snugly over the rod 36. The outer tubular member 39 is cut away to a large extent in order to minimize weight While retaining the strength of tubular construction. At that end remote from the active filament, the portion cut away from member 39 leaves legs 39a extending parallel to, the axis. These legs fit grooves formed in the outer surface of the dielectric ring 43 which supports and separates outer tubular member 39 from the rod-like member 36. The dielectric ring may be held in place bc tween a shoulder on the rod-like member and the inner .tubular member 38, which is secured to rod 36, as by 39a minimizes the conductive heating of the ring. Similar portions are cut away from tubular member 39 at its other end, adjacent the filament, leaving legs 39b. In this instance, however, the legs 39b are all bent radially outward at the same axial level, whereby radially extending fingers 40 are formed. The ends of these fingers are, in turn, bent to a position wherein their elements are parallel to the axis, thereby forming tabs 40a. Similar outward extending radial fingers 41 are formed at the corresponding end of tubular member 38 and extending to points equally distant from the axis as members 40. Fingers 41 are advantageously terminated in tabs 410 like The relative axial positioning of members 38 and 39 is adjusted so that the level of the radial fingers 46 is'the same as that of the radial fingers 41. The portion of tube 39 cut away leaving members 39b permits the free passage of radial fingers 40 past tubular member 39, the radial 'fingers 40 preferably being spaced midway between adjacent fingers 41. The outer tubular member 39 is connected to rod-like conductor 31 by means such as strip connector 44, which is wrapped around ceramic ring 4 43 and welded to each of the legs 39a. This support is essentially the same structure described and claimed in the U. S. application of Joseph W. Skehan, Serial No. 254,329, filed November 1, 1951.

Axial lead. 36, over which tubular member 38 snugly fits, may be extended forming'a member 36a beyond the filament support toward the end of the filament structure, in this case toward the convergent portion of the freehung filament. At the free end of this rod 36a is afiixed resilient bumper member 45. In the alternative, another type of member extending within the filament toward the end of the filament structure remote from the support may be employed for mountingthe bumper. Thus, the support 36a need not be a continuation of'axial rod 36.

Often it may prove convenient to otherwise affix the bumper support member 36a to the filament support. his even possible that the filament support might be by-passed and the bumper support fixed therebelow in any convenient manner. If the bumper support were not afiixed to the filament support structure, it might well be insulated from its support, and, even Where it is alfixed' to the filament support, it may be insulated therefrom if insulation serves any desirable end. Bumper member 45 is affixed adjacent the free end of member 36a. In this instance, the

bumper is composed of a wire member which is spirally wound to a bulbous form and the opposite ends of which are afiixed to the axial rod. Of course, any other'bumper means of suificient resiliency to prevent the shattering of the filament strands 37 upon impact therewithv may be employed. The butnper member should have .a spacing between it and the filament which is somewhat less than the spacing between the filament and the grid. Thus when the filament structure begins to vibrate it will tend to hit the bumper and be damped before it hits the grid or other next adjacent element structure.

The coaxial rings 47 and 48 may be affixed to the grid 7 adjacent electrode, the bumper being spaced from each strand a distance smaller than the spacing between the filament strands and the adjacent electrode, and means supporting the bumper.

2. An electron tube having a filament structure and an electrode adjacent and encircling the filament structure within a vacuum envelope, said filament structure com-j prising a plurality of parallel filament strands circularly arranged, means supporting the filament strands, a resilient bumper member within the circle of said filament strands and spaced therefrom a distance smaller than the spacing between the filament strands and the adjacent electrode, and an axial member supporting the bumper. 3. An' electron tube having a filament structure and an electrode adjacent and encircling the filament structure within a vacuum envelope, saidfilament structure comprising a plurality of parallel filament strands circularly arranged, means supporting the filament strands, a resilient bumper member consisting of a spiral of wire wound to a bulbous form within the circle of said filament strands and spaced therefrom a distance smaller than the spacing between the filament strands and the adjacent electrode, and an axial rod to which the ends of the spiral bumper are afiixcd.

4. An electron tube having a filament structure and an electrode adjacent and encircling the filament structure Within a vacuum envelope, said filament structure comprising a plurality of parallel filament strands circularly arranged and having end portions near one end which converge and are connected to each other, means supporting the filament strands at only one end thereof, a resilient bumper member consisting of a spiral of Wire wound to a bulbous form within the circle of said filament strands and spaced therefrom a distance smaller than the spacing between the filament strands and the adjacent electrode, and an axial rod to which the ends of the spiral bumper are afiixed and which in turn is fixed relative to the filament support.

References Cited in the file of this patent UNITED STATES PATENTS Remane June 6, 1911 Metcalf July 19, 1927 Beardow Aug. 7, 1934 Ronci June 8, 1947 Prideaux Apr. 30, 1940 Miller Oct. 21, 1941 Agule Nov. 10, 1953

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