US2713532A - Electron tube and method of making the same - Google Patents

Description

u y 9, 1955 J. A. M CULLOUGH 2,713,532

ELECTRON TUBE AND METHOD OF MAKING THE SAME Original Filed April 30, 1951 3 Sheets-Sheet l IN V EN TOR. Jack ,4. M9 Cad/00gb BYMif ATTORNEY July 19, 1955 J. A. M CULLOUGH ELECTRON TUBE AND METHOD OF MAKING THE SAME 3 Sheets-Sheet 2 Original Filed April 30, 1951 To Exhqusf Pump IN VEN TOR. Jack A. ME Cul/ough MZ ATTOENE Y July 19, 1955 J. A. MOCULLOUGH 2,713,532

ELECTRON TUBE AND METHOD OF MAKING THE SAME Original Filed April 30, 1951 3 Sheets-Sheet 3 o I a a 29 x a a I VH V K A 7b Exhausf Pump INVEN TOR. Jack A. M Cu//ou h A TTOENEY nsncrnon "runs AND Mansion on MAKING THE SAME Jack A. McCullough, Milliirae, Caliii, assignor to Eitel- Mctflnliough, Inc San Bruno, Calif., a corp-oration of {Talifornia Griginal application April 30, 1%"1, Serial No. 223,7dS. Divided and this application May 16, 852, Serial No. 238,235

4 tClaims. (Cl. 316-49) This is a division of my copending application Serial No. 223,708, filed April 30, 195 l, the present application containing claims to the method and the parent application containing claims to the product.

My invention relates to an electron tube embodying a ceramic construction such as disclosed in the copending application of Harold E. Sorg et al., Serial No. 202,666, now Patent No. 2,647,218, issued July 28, 1953, and more particularly to improvements adapted for small tube structures such as those in the receiving tube category.

Receiving tubes as made in the past have served a good purpose but they have left much to be desired in matters of dependability and ruggedness, the shortcomings being largely due to the mechanical construction of the glass tubes which had grown out of the old lamp industry.

it is among the objects of my invention to overcome the above limitations and to provide a method of making a tube of compact and rugged construction.

Another object is to provide an improved method of making a tube incorporating a ceramic envelope.

A further object is to provide an improved method of assembling and evacuating such a tube envelope.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this dis closure of species of my invention as I may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawings:

Figure l is a plan view of a tube embodying the improvements of my invention; and

Figure 2 is a sectional view of the same taken in a plane indicated by line 2--2 of Figure 1.

Figures 3 and 4 are sectional views showing the tube in a bell jar during the exhaust operation.

In terms of broad inclusion my method of making an electron tube having an envelope of ceramic sections with metalized edges at the joints, comprises the steps of evacuating the envelope while the sections are separated in a bell jar, and then closing the envelope sections and brazing the same together by elevating the temperature of the metalized edges. in a tube having an oxide coated type cathode the latter is also heated to activate the cathode coating during the exhaust operation.

In greater detail and referring to Figures 1 and 2, the improved tube made by my method is shown as a twin triode suitable for tube uses normally classed as receiving tubes. Tubes in this category in the past have been of glass or glass and metal construction with electrode assemblies supported within the envelope by transverse insulators such as mica sheets and the like. In my tube no glass or complicated glass and metal construction is employed, and the internal insulators are eliminated.

The improved tube has the general shape of a flat cylinder and does not involve the usual type of socket arice rangements. For a tube having a plate dissipation of about 15 watts per anode, the tube would be about onethird the size of that shown in Figures 1 and 2. The envelope is made up of four ceramic sections including two disk-shaped end wall sections 2 and two aligned cylindrical side wall sections 3. The end pieces 2 are of identical shape and the side wall pieces 3 are also shaped alike so that actually there are only two different kinds of ceramic pieces used in making up the envelope.

The envelope sections are fitted together along abutting edges, end sections 2 being preferably recessed at the periphery to receive the side wall cylinders and the central abutting edges of the side wall sections 3 being preferably recessed to provide a circular groove for purposes hereinafter described. These ceramic sections are metallically bonded together at the joints to form vacuumtight seals; the side sections being united by a metallic bond 4 and the end sections being united to the side cylinders by the bonds 6. These bonding layers extend along the abutting surfaces between the parts from the inside to the outside of the envelope and also function as lead-in conductors to the electrodes.

The ceramic used in making up the envelope may be of any suitable ceramic-like material, such as the alumina or zircon type ceramic bodies commercially available. Metallic bonds 4 and 6 forming the vacuum-tight seals may be made in several ways, utilizing known metalizing and brazing techniques. For example, the opposed surfaces of the ceramic pieces may be coated with finely divided molybdenum powder, or a mixture of molybdenum and iron powders or the like, and then fired in hydrogen to a temperature of about l500 C. to sinter the metal powder to the ceramic surface. This produces a thin metallic layer firmly bonded to the ceramic. Such metallized surfaces may then be brazed or soldered together with silver solder or brazing alloys such as silver-copper, goldcopper or the like. The brazes are readily made by fitting the metalized ceramic pieces together with rings of wire solder adjacent the joints, and then elevating the temperature of the whole up to the melting point of the solder in a suitable furnace.

in the planar electrode tube illustrated having an indirectly heated cathode, the latter comprises a flat button-like cathode 7 of a metal such as nickel having parallel surfaces coated with an electron emissive material such as the conventional barium-strontium oxides. This cathode is supported by metal ring 8 in which the cathode button is inserted, the ring being engaged along its periphery by the circular groove formed by the recesses previously mentioned in the ceramic side Wall sections 3. The interfitted relationship of these parts also provides means for coaxially aligning the side wall sections when these wall sections are assembled. When the parts are bonded together at the braze 4 the latter provides the cathode lead-in conductor through the side Wall of the envelope.

Cathode terminal 9 on the envelope is preferably formed by a metalized area on the ceramic sections connected to the lead-in braze 4. Thus, when the edges of ceramic sections 3 are treated, as by molybdenum sintering, to metalize the region adjacent the joint, the metalized areas are preferably extended over the outer surfaces to provide a metal band around the body of the envelope to form'the terminal 9.

The heater for cathode 7 preferably comprises a fiat spiral of heater wire 11 embedded in a suitable insulating material 12 within the cathode button. One end of the heater coil is connected to the cathode and the other end brought out through a metal lead 14 brazed in a side wall section 3.

Control grids 16 of the twin triode illustrated are preferably disk-shaped grids having parallel wires fastened to retaining rings 17, these grids being disposed on opposite sides of cathode and parallel therewith. Grid rings 17 are supported on metal leads 18 extending through and brazed to the ceramic end walls 2. There are preferably three of these supporting leads for each of the grids. The holes through which the leads extend are preferably metalized and the leads secured by ceramicto-metal brazes.

in my improved tube the end wall sections 2 of the envelope also serve as the anodes, the inner faces of the ceramic sections being metalized, as by molybdenum sintering to provide the active anode surfaces 19. Ceramics such as the alumina type ceramic bodies are quite good heat conductors and will adequately dissipate the heat in small tubes having relatively low anode dissipation ratings. The areas around the grid leads are not metalized so as to insulate the anode from the grids. A convenient way to do this is to provide recesses 21 around leads 19 and metalize only the flat faces of the ceramic anodes.

Brazes 6 function as the anode lead-in conductors and anode terminals 22 are preferably formed by metalized areas on the ceramic envelope. Thus when the ceramic pieces are treated, as by molybdenum sintering, to metalize the regions adjacent the joint, the metalized areas are preferably extended over the outer surfaces to provide metal bands around the body of the envelope to form the terminals 22.

The brazes at the joints and metalized areas are shown as having appreciable thickness for convenience of illustration. Actually, these are quite thin metal layers, say of the order of 0.002" to 0.005 thickness, and appear as films or metal skins on the surfaces of the ceramic. If desired, silver, copper or the like may be electroplated and/or flowed over the sintered areas to further improve the electrical conductivity. Copper or silver plating on the sintered areas, for example, make excellent terminal surfaces and is ideal for brazing together at the joints either with or without the use of additive brazing material.

The improved method of pumping the tube embodyan exhaust pump. At the stage shown in Figure 3 the 7 tube preferably comprises three subassemblies, namely, the central assembly comprising cathode 7 mounted on the previously brazed wall sections 3, and the end assemblies comprising grids 16 mounted on anode sections 2. These three units, with the end assemblies separated from the central assembly, are held by any suitable fixture (not shown) so that the space betweenthe tube parts is evacuated when the bell jar is exhausted. Such fixture is so arranged that the end assemblies are permitted to collapse together against the central assembly to close the envelope after exhaust of the bell jar.

When using this exhaust procedure the final brazes between ccramic sections 2 and 3 are made in the bell jar. The brazing material, such as silver or copper, is previously applied to the ceramic parts by electroplating and/or flowing the metal over the sintered areas as hereinbefore mentioned. The final brazing operation then merely involves bringing the temperature of the end joints in Figure 4 up to the melting point of the metalto-metal surfaces.

My preferred procedure is as follows: with the envelope assemblies in the open position shown in Figure 3 the bell jar is first exhausted to a hard vacuum. All the tube assemblies are then preferably heated sufficiently to outgas the tube parts. This corresponds to the usual bake out step; the added advantage in my process being that the tube is open at this time so that the gases are quickly pumped away, resulting in a more complete outgassing of the parts. A simple way of heating the parts for bake out purposes is to use a metal cylinder 27 in the bell jar heated by induction from an external radiofrequency coil 28.

After outgassing the tube parts the oxide cathode 7 is activated. This is also done while the envelope is in the open position shown in Figure 3. Activation of the cathode coating is accomplished by heating the cathode with heater E1 to the proper forming temperature in the usual manner, the heater current being supplied in my case through suitable leads entering the bell jar and connected to the heater terminals. The added advantage in my process is that cathode activation takes place without danger of contaminating the grids and other vital parts of the tube. This overcomes a serious problem in the making of oxide coated types of tubes, because ordinarily tube parts such as grids which are closely spaced to the cathode are vulnerable to contamination by barium and other active agents volatilized from the coating during cathode formation. With my procedure there is much less likelihood of such contamination because the gridanode assemblies are further separated from the cathode; and the envelope being open allows the volatile constituents to be quickly pumped away.

Alter the cathode has been formed, the end assemblies are moved into position against the side wall sections to close the envelope as shown in Figure 4, and the final brazes are made by bringing the temperature of the metalized ceramic end joints up to the melting point of the metal-to-rnetal surfaces. Such heating is preferably 10- calized at the joints, as by radiation from adjacent heater coils 2%. Upon completion of the brazes the exhaust pump is shut off and the completed tube is ready for removal from the bell jar.

l claim:

1. The method of making an electron tube having an envelope with wall sections adapted to be bonded together at a joint, which comprises the steps of positioning the tube in a vacuum chamber with the wall sections separated an appreciable distance apart to allow free movement of gas from the interior of the envelope to the chamber, evacuating the envelope while the walls are so separated and then bodily displacing the walls to close the envelope and bonding said walls together while the tube is in the vacuum chamber.

2. The method of making an electron tube having an envelope with ceramic wall sections having metalized edges adapted to be brazed together at a joint, which comprises the steps of positioning the tube in a vacuum chamber with the wall sections separated an appreciable distance apart to allow free movement of gas from the interior of the envelope to the chamber, evacuating the envelope while the walls are so separated, and then bodily displacing the walls to close the envelope and brazing the metalized edges of said walls together while the tube is in the vacuum chamber.

3. The method of making an electron tube having an oxide coated tube of cathode and an envelope with Wall sections adapted to be bonded together at a joint, which comprises the steps of positioning the tube in a vacuum chamber with the wall sections separated an appreciable distance apart to allow free movement of gas from the interior of the envelope to the chamber, evacuating the envelope while the walls are so separated and at the same time heating the cathode to activate the cathode coating, and then bodily displacing the walls to close the envelope and bonding said walls together while the tube is in the vacuum chamber.

4. The method of making an electron tube having an envelope with wall sections adapted to be bonded together at a joint, which comprises the steps of positioning the tube in a vacuum chamber with the wall sections separated an appreciable distance apart to allow free movement of gas from the interior of the envelope to the chamber, evacuating the envelope while the walls are so separated and at the same time elevating the temperature of the envelope to outgas the same, and then bodily displacing the walls to close the envelope and bonding said walls together while the tube is in the vacum chamher.

References Cited in the file of this patent UNITED STATES PATENTS Ziegenbein Dec. 27, 1938 Ronci Jan. 6, 1942 Beggs Oct. 7, 1947 Eitel Oct. 30, 1951 Sorg et al July 28, 1953

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