US2908842A - Filament tensioning - Google Patents

Description

Oct; 13, 1959' J. KUFFER FILAMENT musxoumc Filed Feb. 25. 1957 2 Sheets-Sheet 2 A Fla. 7

Fla. 8

INMENTOR JOHANNES KUFFER PATENT AGENT United States Patent (Nice FILAMENT 'IiENSIONlNG Johannes Kiilfer, Ulm (Danube), Germany, assignor to Telefunken G.rn.b.H., Berlin, Germany ApplicationFebl-uary 2-5, 1957, Serial No. 641,922

7 Claims. (Cl. 313-273 The present invention relates to a method and device for tensioning the filament in an electron tube, particularly, a directly heated electron tube, by means of a spring attached at one of its ends to one end of'the filament and at its other end to a fixed point of the device.

Such arrangements have been known per se. In one of the known structures of this kind, the filament is mechanically tensioned by providing a double-arm supporting means for pre-tensioning the spring, whereby the arms of this supporting means originally form an angle of about 90. One of the arms is mounted on a fixed point of the structure and the other arm is attached to one end of the spring, while the other end of this spring is attached to the filament. After connecting the free end of the spring to the filament, the two arms of the supporting means are bent toward each other so that the springis mechanically biased, whereby the filament is simultaneonsly'tensioned. This known tensioning device for filaments in electron tubes has certain disadvantages, because the assembly is dependent to a certain extent upon the dexterity and reliability of the worker who may not uniformly tension all of the filaments during mass production.

It is an object of the present invention to provide independence from these uncertainties in the manufacture and assembly of filaments in electron tubes.

It is another object of the invention to provide a predetermined mechanical spring bias in such devices and to release this bias after mounting the filament.

It is a further object of the invention to attach the spring first to a support and then bend the latter in such a manner that the spring becomes biased by distortion; subsequently to attach one of the ends of the support member to the tube structure and the free end of the spring to the free end of the filament; and finally to bend or otherwise remove the bent end of the support member which end originally distorted the spring, thereby freeing the spring to tension the filament.

As a result of this, each filament will be under uniform tension, because the tension is dependent upon the predetermined mechanical properties of the spring. This support member becomes part of the structure of the tube, the geometrical dimensions of which are standardized during manufacture.

If the bent end of the support member biasing the spring is not removed to restore the spring tension, but is merely bent back to such extent that it no longer contacts the spring, even when the filament expands due to heat, another purpose will be served. In this case, the end of the spring serves simultaneously as a mechanical stop for the spring, should the filament break. Indeed, considerable damage may occur with tubes of this type, due to sudden release of the spring in case of a filament break, the spring striking another structural element at a different electric potential and causing a discharge of the circuit via the two elements. In most instances, the getter at anode potential will be the element struck by the spring during its movement. This 2,908,842 Patented Oct. 13, 1959 disadvantage is overcome by the method and the design according to the present invention.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

In the drawings:

Figures 1 and 2 illustrate side views of two different embodiments of the whole supporting structure accord ing to the invention, the tubes themselves being not shown.

Figure 3 shows a front view of a support member used in the structure according to the invention, at one stage of its manufacture.

Figure 4 is a side view of the same support member illustrated in Figure 3.

Figure 5 shows a side view of this support member at another stage of its manufacture.

Figures 6 and 7 illustrate a modified embodiment of the support member in front view and side view, respectively.

Figure 8 shows an assembly of the modified embodiment of the device according to this invention, in which the support member of Figures 6 and 7 is employed.

Figures 4, 5 and 8 show only those parts of the tube structure which are necessary to explain the invention.

In'Figures 1' and 2, 1 and 2 denote a lower and an upper sheet of mica, while 3 is a spacer member in the tube, for example, a supporting bar. One end of the heater filament 5 is secured to the lower mica sheet 1 by means of a filament holder 4. The upper end of the filament 5 ending in a small tab 8 is secured to a support device 6 by means of a whip spring 7. This arrangement is shown in detail in Figures 3, 4 and 5.

If the support device 6 is associated with a whip spring 7, the former is made of a U-shaped, punched metal sheet on which the spring 7 is mounted in such a manner that it extends parallel with respect to the portion of the sheet metal plate joining the two legs of the U. This spring 7 is spot-welded at 14 to one leg of the supporting device 6. A side view of this device is shown in Figure 4. The U-shaped support device 6 is subsequently bent at a right angle about the line 16, as is shown in Figure 5. For the sake of superior manufacture, the spring 7 is welded to the support device 6 and the latter bent about the line 16 in a single operation. Since the spring 7 is mounted on one of the legs of the support device 6, the spring will be likewise bent to a right angle. The device, as shown in Figure 5, is now attached to the spacer 3 and to the free end of the filament 5, for example, by spot-welding (see Figure 1). After the parts have been assembled in this manner, it is merely necessary to release the spring 7 which, according to the embodiment shown in Figure 1, is effected by bending back the upper part or leg of the support device 6 to the position 9, shown in dot-dash lines. The bent back portion at 9 of the support device 6 serves now as a stop for the spring 7 in case of a filament break. If, in such a tube a getter 10, which may be at anode potential, is provided and located as shown in Figure 1, the spring 7, when suddenly freed, will be prevented from striking this getter 10 during the sudden upward movement.

If such mechanical protection is not necessary, the free end of the suspending device 6 may be removed by cutting off this metal piece either at 15, 16 or 17 (see Figure 3). The assembled support device 6, in case of this modification, is shown in Figure 2. In case of a break of the heater filament 5, the spring 7 suddenly snaps upwardly to the position indicated in a dash-dot line at 11 moving through an are 12.

In the embodiment illustrated in Figures 6, 7 and 8, the spring secured to the filament is designed as a coil spring. According to Figure 6, a support device 18 constituting a sheet metal stamping in the'shape of the letter E is provided, and a coil spring 19 is placed on the center leg 22 thereof. The two outer legs 20 and 21 of this support 18 serve as abutments for the two spring ends. One of the spring ends may be attached to one of the outer legs, for example, by spot-welding at 12a, to the leg 20, while the other leg 21, in substantially the same manner as in Figures 1 and 2, will be either bent (see Figure 8) or cut 011 after the filament has been secured to the distorted spring 19. In case of a break of the heater filament 5, the upper end portion of the spring 19 snaps back to a limited extent only, because the angular displacement 23 of this spring portion is limited by the bent leg 21 serving as a stop for the spring portion, so that the getter cannot be struck thereby.

I claim:

1. The method of mounting a filament without tension between a fixed holder and a spring and then tensioning the filament, including the steps of predistorting the spring through a selected distance within the elastic limit of the spring by applying a distorted member directly between the extremities of the spring, holding the spring so distorted, connecting the untensioned filament between the holder and the predistorted spring, and subsequently releasing the spring by displacing the distorting member.

2. A tensioning device for use in mounting a filament in an electron tube having a filament holder to which one end of a filament is fixed, comprising a support member having one leg fixed in the tube and spaced from said holder and having another leg bent toward said holder;

a spring attached to said fixed leg and having a free end distorted toward the holder and maintained thereat by said bent leg, the free end of the spring being joined to the free end of the filament prior to release of the spring by retraction of the bent leg.

3. In a device as set forth in claim 2, said bent leg when retracted being moved only out of contact with the spring but left adjacent thereto to act as a spring stop in the event of filament breakage.

4. In a device as set forth in claim 2, the bent leg being broken ofi during said retraction.

5. In a device as set forth in claim 2, said support member being a U-shaped sheet metal stamping, and said spring being a whip spring secured to one leg of the U and distorted by bending of the other leg of the U to maintain the spring arched.

6. In a device as set forth in claim 2, said support member being an E-shaped sheet metal stamping, and said spring being a coil spring mounted around the center leg, one end of the spring resting against ont outside leg and the remaining leg being bent over to bias the free end of the spring toward the filament holder.

7. In a device as set forth in claim 2, the spring being mounted on the support member before being distorted by bending of said leg.

References Cited in the file of this patent UNITED STATES PATENTS 1,615,654 Ryder Ian. 25, 1927 1,657,221 7 Metcalf Jan. 24, 1928 1,720,442 Robinson July 9, 1929 2,092,886 Kiihle Sept. 14, 1937 2,506,895 Sassaman May 9, 1950 2,770,753 Moesker Nov. 13, 1956 2,789,243 Gowell Apr. 16, 1957

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