US2899590A

US2899590A - Ceramic vacuum tube

Info

Publication number: US2899590A
Authority: US
Publication date: 1959-08-11
Anticipated expiration: 1976-08-11

Description

Aug. 11, 1959 H. E. SORG ETAL 2,899,590

CERAMIC VACUUM TUBE Filed March 9, 1953 3 Sheets-Sheet 2 INVENTORS Hare/o E. Sorg Louis /7. La ForgeJn ATTORNEY Aug. 11, 1959 H. E. SORG EI'AL CERAMIC VACUUM TUBE Filed March 9, 1955 3 Sheets-Sheet 3 /m Y m m m R waw go L T M m5 m1 Y United States Patent G CERAMIC VACUUM TUBE Harold E. Sorg, Redwood City, and Louis H. La Forge, Jr., Palo Alto, Calif., assignors to Eitel-McCullough, Inc., San Bruno, Califl, a corporation of California Application March 9, 1953, Serial No. 341,122

4 Claims. (Cl. 313-250) Our invention relates to electron tubes and more particularly to tubes having ceramic envelopes.

The principal object of our invention is to improve the ruggedness and reliability of vacuum tubes so as to reduce the number of tube failures heretofore experienced in both military and commercial electronic equipments. Experience has proven that failures are largely due to the fragile construction of conventional tubes, principally because of the inherent weakness of structures incorporated in tubes having glass envelopes.

Our improved construction, having a ceramic envelope, brazed joints and adequately supported electrodes, provides a tube which is reliable and dependable even under adverse conditions such as shock and vibration and elevated temperature environments.

Another important object of our invention is to provide a tube structure which is designed to facilitate fabrication and which is adaptable for automatic assembly operations.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt variant embodiments thereof within the scope of the claims. 3 e

Referring to the drawings:

Figure 1 is an exploded view of a triode type of tube embodying our invention.

Figure 2 is a perspective view of the tube; and

Figure 3 is a vertical sectional view of the same.

Figure 4 is an exploded view of a twin triode type of tube embodying our invention; and

Figure 5 is a perspective view of the completed tube.

Figure 6 is a plan view of the tube with an end wall removed to show the internal structure.

Figure 7 is a vertical sectional view taken in a plane indicated by 77 of Figure 6; and,

Figure 8 is a similar view taken in a plane indicated by 8-8 of Figure 6.

In greater detail, our improved tube structure comprises an all-ceramic envelope which has the general shape of a flat cylinder. The tube structure is adaptable to a variety of electrode assemblies, such as triodes, tetrodes, twin triodes, twin tetrodes, etc. The term electrode is used in its broad sense herein, and includes any tube element connected to a voltage source or having a potential differing from that of another element. Figures 1 to 3 show a simple triode structure, and this will be first described.

The vacuum-containing envelope of our tube comprises but three pieces, namely, a side wall cylinder 2 and two end disks 3 and 4 which fit into the ends of the cylinder. These parts are of ceramic metallically bonded together along the upper and lower joints 6 and 7. The ceramic used in making up the envelope is a dense refractory body, such as an alumina type ceramic. Such ceramics Patented Aug. 11, 1959 ICC have good mechanical strength and are able to withstand high temperatures. Other commercially available ceramics, such as the zircon type bodies, may also be used.

The ceramic-to-ceramic seals may be made in several ways using known metallizing and brazing techniques. For example, the opposed surfaces of the ceramics at the joints may be coated with finely divided metal powder and fired to sinter the metal particles to the ceramic. A satisfactory procedure is to coat with a mixture of molybdenum and manganese powders and fire in hydrogen to a temperature of about 1350 C. This produces a thin layer firmly bonded to the ceramic. The sintered area is then preferably electroplated with nickel to produce a solid metal surface. Another metalizing technique is to paint titanium or zirconium hydride powder on the ceramic and fire in vacuum to about 1200 C.

The metalized ceramics may then be brazed or soldered together with silver solder, or brazing alloys such as silver-copper, gold-copper, or the like. The brazes are readily made by fitting the ceramic envelope sections together with rings of wire solder adjacent the joint and then elevating the temperature of the whole up to the melting point of the solder in a suitable atmosphere. Such brazing is, of course, done after assembling the internal portions of the tube structure.

An important feature of our invention has to do with the electrode assembly within the envelope, which improved structure provides a simplified electrode arrangement, more adequate support for the electrodes, and facilitates putting the tube together. In our tube the ceramic wall cylinder 2 functions as a retaining collar or sleeve into which the electrode assembly is stacked. The stacked assembly comprises disk-shaped cathode and grid electrodes 9 and 8 and ceramic spacer rings 11 and 12 sandwiched together and fitted in the ceramic cylinder 2 between the ceramic end disks 3 and 4.

Cathode 9 is pressed out as a boss from a metal disk, preferably of nickel, so that the flat portions of the disk form a radially extending support 13 for the cathode. In the final assembly this cathode piece sets down on the bottom end disk 4 as seen in Figure 3. Lead-in connection to the cathode is provided by the metallic layer at joint 7, a metalized area 14 being provided on the inner peripheral surface of ceramic disk 4 (Figure 1) to make contact with the cathode support 13. A metalized area is also provided across the end of ceramic cylinder 2 and on the lower outer surface of the cylinder to serve as a terminal 15 for the cathode.

The top of cathode 9 is coated with a suitable electron emissive material 16, such as the conventional bariumstrontium oxides. Cathode 9 may have a fiat top facing the grid, but we preferably provide some degree of curv ature as shown in Figure 3. The heater for the cathode preferably comprises a flat spiral of heater wire 17 embedded in a suitable insulating material 18. One end of the heater coil is connected to cathode body 9 and the other end is brought out through a metal pin 19, the latter being brazed to a metalized hole in the ceramic disk 4.

Grid 8 is spaced from the cathode by ceramic ring 12. Since these ceramic bodies may be ground to close tolerances, the grid-to-cathode spacing is accurately determined. The grid is preferably a wire mesh having a curvature to match the cathode, which curvature gives stability to grid. The grid mesh is fastened to an apertured metal disk providing a radially extending support 21 for the grid. The grid, in turn, is spaced from the upper wall disk 3 by the ceramic spacer ring 11. Metal pin 22 brazed in a metalized hole in ceramic disk 4 provides a lead-in connection for the grid. This pin preferably projects through spacer ring 12, through grid support 3 21 and into spacer ring 11, so that it also functions as an alignment pin for the stacked electrode assembly. An oversize hole 23 in cathode support 13 avoids contact between the grid pin 7 and) cathode.

Anode 24.0f our t-ubeis formed by metalizing the inner surface of the ceramic end disk, the latter having a dished recess at the active anode area to provide a curvatiure matching the grid and'cathode.

has fairly good heat conductivity, a reasonable amount of heat may be dissipated from the anode through the ceramic, which is suflicient for many vacuum tube applications. If more dissipation is required, the end wall disk 3 may .be'made of metal brazed to the-metalized rim of ceramic cylinder 2. In the all ceramic construction themetallic bond at joint 6 preferably serves as the anode lead-in conductor, the rim portions of ceramic cylinder 2 being also metalized to provide the anode terminal 26.

Our construction above described is adaptable to tube types having other electrode arrangements. 1 For example, if a tetrode is desired, it is only necessary to make cylinder 2 somewhat larger and add a second grid structure (screen grid) and include another spacer ring.

Figures 4 to 8 show how the construction'is adapted to a twin triode. In this case, the cathode is in the form of a button generally designated at 27 and located centrally of ceramic wall cylinder 28 between ceramic spacer rings 29'and 31.

Grids

32 and 33 are held between the

ceramic end disks

34 and 36 and the adjacent ceramic rings. Both end disks are metalized on the inner surfaces to form the

anodes

37 and 38. Supporting

tabs

39 and 41 on the grids are bent inwardly withrespect to the end disks to provide the desired spacing from the anodes.

In this twin triode construction, the metallic bonds or brazes at the end joints of the envelope are preferably used as lead-in conductors for the grids, metalized rim portions on ceramic cylinder 28 providing the

grid terminals

40 and 45. The metalized areas for the

anodes

37 and 38 are limited to the central regions of the end disks, and anode terminals :are provided by pins 42. and 43 extending inwardly to the coated areas.

Cathode'button'27 is supported by radially extending metal tabs 44 held between the spacing rings 29 and 31. As shown in Figure 6 the tabs 39 of grid 32 are angularly displaced with respect to supporting tabs 44 of the cathode. Lead-in connection for the cathode is provided by a pin 50 extending through end Wall 34, spacer rings 29 and 31and' through one of the cathode supporting tabs 44; 'See Figure 8. 46 and 47 are provided for the cathode heater. Figure 7.

The cathode is' formed by two cupped pieces of metal 48, say of nickel, joined together to provide a hollow but- See ton; Opposite sides'of the cathode, each facing one of the grids, are coated with an electron emissive material. The cathode heater comprises a flat spiral of heater wire 49'embedded in an insulating material 51, 'the' ends of the wire being brought out and fastened to tabs52 which connect with the

pins

46 and 47.

Our twin structure is also adapted for other electrode arrangements; thus, the addition of a second spacer ring and another grid (screen grid) in each half of the tube provides a twin tetrode.

Our improved structures, whether of the single or twin type,-are easy to assemble because all are designed on the principle of stacked electrodes. The ease of assembly comes about because the electrodes and spacer rings are slidably fitted in the ceramic wall cylinder, which cylinder-thus functions both as a retaining sleeve and as a wall of the evacuated envelope. Since the stacked parts Within the retaining sleeve are merely a mechanical assembly and do not involve vacuum-tight joints, such parts may be readily put together. In our tubes one of the ceramic end wallsis preferably first brazed to the ceramic Since the ceramic A pair of similar pins side wall. to provide a cup-shaped structure. The internal parts are then stacked in place. Lastly, the second end Wall or lid is inserted and brazed.

Our tube structures may be provided with exhaust tubulations (not shown) and evacuated in the conventional manner, or the tubes may be evacuated in a bell-jar type of exhaust system. In the latter case the second end wall is notbrazed-in place until after the exhaust operation.

In'the drawings'the'metalized areas and brazed joints are shown as havingapprecia-ble thickness for convenience of illustration. Actually, these are quite thin metallic layers, say of the order. of 0.005 thickness, and appear as films or metal skinson the surfaces of the ceramic.

The lead-in pins 19 and 22 in Figure 1 and

similar pins

42, 43, 46, 47 and 50 in Figure 4 have been described as metal pins brazed to metalized holes in the ceramic. Instead of being .of metal, these pins may also be of ceramic. In the: latter; case the ceramic pins are first metalized and then brazed to the metalized holes in the ceramic, thepins beingmetalized-along their entire length to provide-the. desired conductivity; The advantage of a ceramic lead-in pinis that it has a coefficient of thermal expansion. identical with that of the ceramic of the envelope, thus reducing" the. possibility of cracklng the ceramic envelope, which might occur if the materials had diiferential expansions.

We'claim:

1. An electron tube comprising an envelope; having a side wall cylinder of ceramic and end wall disks sealed vacuum-tight to opposite ends of said cylinder, a stacked electrode assembly in said envelope comprising ceramic spacer rings and disk-shaped electrodes fitted into. said cylinder, each of said disk-shaped electrodes having supporting tabs extending radially therefrom, the supporting tabs of one of said electrodes being angularly displaced with respect to thoseof an adjacent. electrode, a first lead-in pinsealed through-one of said end wall disksand extending through said spacer ringsinto electrical contact with one of the supporting tabs of one of said elec-v trodes, and a second lead-in pin sealed through said one end wall disk at a point angularly displaced from ,said first lead-in pin and extending through said spacer rings into electrical contact .with one of the supporting tabs of said adjacentelectrode, the inner surface of each of said end wall disks being in contact with said electrode assembly. 7

2. An electron tubecomprising anenvelope having a side wall cylinder of ceramic and end. wall disks sealed vacuum-tight to opposite ends of said cylinder, the inner surface of one. of said end Wall disks being metallized to provide ananode, a disk-shaped cathode mounted on the inner surface of the other of said end wall disks, a pair of ceramic rings fitted'within saidcylinder, a diskshaped grid electrode within said cylinderhaving a radially extending support member sandwiched between said pair of ceramic rings, and a lead-in pin sealed through said other end wall disk in insulated relation to said cathode and extending through one of said'ceramic rings into electrical contact with said support member of said grid electrode.

3. An electron tube comprising an envelope having a side wall cylinder of ceramic and end walldisks sealed vacuum-tight to opposite ends of said cylinder by means of a metallic seal, a central portion of the innersnrfac'es of said end wall disks being metallized to provide anodes, a stacked electrode assembly in said envelope comprising diskshaped cathode and grid electrodes and a pairof ceramic rings fitted within said side wall cylinder, said cathode and grid electrodes being provided with radially extending support tabs, thesupport tabs for said cathode being sandwiched =-between said pair of rings, the support tabs for said grid 'electrode being angularly displaced fromthose of said cathode and being sandwiched between one'ring of said pairof rings and one of said end walls,

a first lead-in pin sealed through one of said end walls in insulated relation to said metallizing thereon and eX- tending through the intervening spacer rings into electrical contact with one of said support tabs on said cathode, and a second lead-in pin sealed through one of said end walls and extending into electrical contact with said metallizing thereon, said support tabs on said grid extending into electrical contact with said metallic seal between one of said end walls and said side wall cylinder, the inner surface of each of said end wall disks being in contact with said electrode assembly, and peripheral portions of said electrode assembly being in contact with the inside wall of said cylinder.

4. An electron tube comprising an envelope having a side wall cylinder of ceramic and end wall disks sealed vacuum-tight to opposite ends of said cylinder, a stacked electrode assembly in the envelope comprising a diskshaped electrode and ceramic spacer rings sandwiched together and fitted within said side wall cylinder between the end disks, said electrode having a radially extending support held between said spacer rings, and a pin pro jecting through one of said end disks and providing a lead-in conductor for said eletcrode, said pin extending through one of said spacer rings and electrically connected to said electrode support.

References Cited in the file of this patent UNITED STATES PATENTS 1,561,249 Kraut Nov. 10, 1925 2,113,005 Smith Apr. 5, 1938 2,229,585 Osenberg J an. 21, 1941 2,343,849 Binneweg Mar. 7, 1944 2,408,822 Tanis Oct. 8, 1946 2,425,593 Brian Aug. 12, 1947 2,441,792 Brian May 18, 1948 2,451,297 Moore Oct. 12, 1948 2,459,277 Halstead et a1. Jan. 18, 1949 2,731,578 McCullough Jan. 17, 1956 2,808,528 Martin Oct. 1, 1957