US2677782A

US2677782A - Vacuum tube heater

Info

Publication number: US2677782A
Application number: US192442A
Authority: US
Inventors: Forrest E Gehrke; William T Granger
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1950-10-27
Filing date: 1950-10-27
Publication date: 1954-05-04
Anticipated expiration: 1971-05-04

Description

y 4, 1954 F. E. GEHRKE ETAL 2,677,732

VACUUM TUBE HEATER Filed Oct. 27, 1950 INVENTORS FORREST E. GEHRKE WILLIAM T. GRANGER Patented May 4, 1954 VACUUM TUBE HEATER Forrest E. Gehrke, Huntington, and William T.

Granger, Floral Park, N. Y., assignors to Vania Electric Products Massachusetts Syl- Inc., a corporation of Application October 27, 1950, Serial No. 192,442

'7 Claims. 1

This invention relates to tubes.

In the manufacture of heaters for vacuum tubes, it has been known to wind the heater wire in the form of a coil around a, heavier mandrel wire, the latter being first coated with insulation to avoid short-circuiting the heater turns. Difficulties have been experienced with such heaters, these commonly being burnouts of the heater during exhausting and aging of the tubes.

While we do not wish to be bound to our theory as to the probable causes of these burnouts, it was concluded that they may be due to the develop-- ment of pressure between the heater and mandrel due to differences in expansion of the heater and mandrel respectively, and/or due to the migration during processing and operation of the tube, of metal into the body of insulator between the heater and mandrel rod to an extent sufiicient to cause the formation of a conductive path between the heater winding and the mandrel core. This would in eiiect short circuit a portion of the heater and overheat the remainder. It was considered that these difficulties could be reduced if heaters for vacuum some way could be found to wind the heater on the mandrel so as to leave at least some open space between the mandrel and the heater wire.

By following the method hereinafter described, applicants found it possible to produce a mandrelsupported heater with a space between the mandrel and heater wires.

It is an object of this invention to provide a mandrebsupported heater which is less subject to burnouts than the conventional mandrel-supported heaters.

It is a further object of this invention to provide a mandrel-supported heater with a space between the mandrel and the heater.

It is a further object of this invention to pro vide a method for producing such a mandrel-supported heater.

Still other objects and advantages of our invention will be apparent from the following specification.

The features of novelty which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, both as to its fundamental principles and as to its particular embodiments will best be understood by reference to the speciiication and accompanying drawing in which Figure 1 is a view of a vacuum tube with a heater according to our invention, parts of the tube being broken away in the drawing for simplicity.

Figure 2 is a perspective view of an insulated mandrel at one stage of the practice of our in vention.

Figure 3 is greatly enlarged longitudinal section of a portion of the arrangement of Figure 2 after it has been coated according to our invention and the heater wire wound in position.

Figure 4 is a similar view after part of the coating has been removed in accordance with our invention, and

Figure 5 is a similar view of the heater and mandrel after completion and Figure 6 a completed heater.

Referring now more particularly to Figure l,

t represents the mandrel supported heater as frequently used in a vacuum tube, the heater being supported within a hollow, tubular cathode it mounted in a central aperture in mica supporting discs i2 and E3. The ends of the heater wire are connected to leads it which pass out through the base of the tube. The electrode ssembly or mount is positioned in envelope E5. The cathode ii is surrounded by a suitable arrangement of grids and an anode which are here not specifically identified since they form no part of the present invention.

The connections from the ends of the heater wire may go directly to the leadein wires iii or the upper end of the heater wire may be connected to the mandrel and it is used for one connection, the other being made to the other end of the heater wire. Such construction is described in more detail in a Wheeler application Serial Number 50,946 filed September 24, 1948, and assigned to the assignee of the present application.

Referring now more particularly to Figures 2 to 5, the mandrel wire it is first coated with a suitable insulating agent ll, such as aluminum oxide and sintered to fix it into a hard coat. Because such insulated mandrels are commonly available and because in the practice of our invention we start with conventional insulated mandrels, the same are not described in detail.

In accordance with our invention, we apply a special coating ila to the insulated mandrel. This coating consists of an intimate mixture, emulsion or solution of two different substances having diiierent solubility characteristics uniformly dispersed in a liquid carrier vehicle. As an example, We may use a mixture of cellulose acetate and methyl methacrylate (commonly called Lucite) in acetone. The mandrel is coated with this and allowed to dry and the heater wire wound about it. This is the state of the heater shown in Figure 2. While we do not wish 3 to be bound by any theory, we believe this forms a coating with fine particles of cellulose acetate and Lucite intimately mixed in the manner shown in Figure 3 in which l8 represents finely divided particles of cellulose acetate, and i9 similar particles of Lucite.

After the heater has been wound and tabbed with suitable connection pieces the assembly is placed in benzene for several hours. Because Lucite is soluble in benzene and cellulose acetate is not, a selective dissolving action occurs removing the Lucite particles and leaving the cellulose acetate particles. Microscopic examination of the assembly at this point shows the coating to be in the form of mounds of adherent particles such as shown in Figure 4, with the heater wire resting on the peaks of these mounds thereby preventing the shifting of the wire and maintaining control of turn spacing.

The assembly is then coated with its fnal in sulation which tends to fill in the spaces left by the removal the Lucite particles. It then fired which burns out the cellulose acetate as well as sinte the final insulation into a dense unitary coating. The cellulose acetate. being slow burning, does not cause the insulation. to chip as bu ning material would. The burning out oi the cellulose acetate leaves voids iii where the acetate particles were, indicated in Figure 5, but the turns of the wire are prevented from axial shitting by the outer insulating coating which extends inwardly between the wire turns into the valleys between. the mounds and to some extent, into the voids left by dissolving out the Lucite. ihe layer of insulation. between wire and manorcl i'i in its final state may be cl'iaracterized being spongy, that is, as an open porous body with substantial voids and cavities therein.

The result of this is a mandrel-supported heater in which the heater turns are held in their proper space relation while at the time there is sufiicient spacing between the heater turns and the mandrel to prevent th develop-- ment of pressure between them due to "erences in expansion of the mandrel and heater coil. The general appearance of a completed heater is as indicated in Figure 6, one end of the heater wire being internally connected to mandrel wire iii and the other to tab 35 whereby both heater con nections may be made at the same end of the assembly. However our invention is not limited to the particular physical arrangement shown.

While we have given an example the use of a coating of cellulose acetate and Lucite acetone, it will be clear that we are not lin.ited thereto, but may use other plastics provided they have different solubility characteristics so that one may be dissolved out by selective action, leav ing the other.

While we have shown and described certain preferred embodiments of our invention, it will be apparent that modifications and changes may 4 be made without departing from the spirit and scope of our invention as will be clear to those skilled in the art.

What we claim is:

l. A new article of manufacture, comprising a mandrel-supported heater having a core, a coating of insulation thereon, a heater surrounding mandrel and having substantially open space between said heater and said coating of insulation and a coating of refractory insulation surrounding said heater.

2. A new article of manufacture comprising a mandrel-supported heater having a core, a coating of insulation thereon, a heater wound around said coating and spaced radially from said ooating and a coating of insulation surrounding said heater and projecting inwardly between the turns thereof.

3. A new article of manufacture comprising a vacuum tube having a heater element including an insulated mandrel, a heater wound helically around said mandrel in spaced relation thereto and a coating of refractory insulation surrounding said heater and projecting inwardlybetween the turns thereof.

a. A new article of manufacture comprising a mandrel-supported heater having a wire core, a coating of insulation thereon, a heater coiled around said mandrel and spaced therefrom, an outer coating of insulation surrounding said heater, the space between said. mandrel said heater containing a substantial amount of open space.

A heater for electron discharge devices ineluding a refractory insulating core, a helical heater surrounding said core in spaced relation with respect to said core and a coating of refractory insulation surrounding said heater winding and projecting inwardly between the turns thereof.

5. A heater for electron discharge devices including a refractory insulating core, a heater helically wound in a spaced away relationship with said core and a coating oi refractory insulation surrounding said heater winding and pro-- iecting inwardly between the turns thereof and resting against said refractory insulating core.

2. heater electron discharge devices incluclg an inner refractory core, a spongy coating or refractory material over said core, a heater wire wound helically around said porous coating and an outer coating of refractory insulation surrounding said heater.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,975,870 Schradcr -l Oct. El, 1934 1,980,675 Fredenburgh Nov. 13, 1934 2,131,909 Umbreit Oct. 1938 2,43%,511 Osterman et al l Jan. 13, 1948 2,455,355 Combs, E. E. Dec. 7, 1948