US2118002A - Electron discharge tube - Google Patents

Description

y 1938- R. G. BENNETT 2,118,002

ELECTRON DI S CHARGE TUBE Filed April 8, 1937 INVENTOR,

ATTORNEY Patented May 17, 1938 UNITED STATES PATENT OFFIQE Hygrade Sylvania C orporation, Salem, Mass,

a corporation of Massachusetts Application April 8,

11 Claims.

This invention relates to electron discharge tubes and more particularly to shielding means for such tubes.

A principal object of the invention is to provide an improved form of getter shield for radio tubes and the like.

A feature of the invention relates to an improved means for securing a shielding member, for example a getter shield, in position within a radio tube or similar device. I

A further feature relates to a radio tube of the metal envelope type wherein a getter shield of ceramic or other insulating material is employed in conjunction with a novel form of fastening means to hold the shield in place.

Another feature relates to an improved form of metal clip for fastening an insulator member, for example, a getter shield, within a radio tube or the like.

A still further feature relates to the novel organization, arrangement and relative location of parts which go to make up an improved radio tube of the metal envelope type.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the invention will be illustrated as embodied in a radio tube of the metal envelope type, it will be understood that certainaspects of the invention are not necessarily limited to this type of tube and can be equally well embodied in a wide variety of tubes and similar devices. Accordingly in the drawing,

Fig. 1 is a vertical sectional view of a metal radio tube embodying features of the invention and taken along the line II of Fig. 2.

Fig. 2 is a sectional view of Fig. 1 taken along the line 2-2 thereof.

Fig. 3 is a side elevational view of the tube mount of Fig. 1, with the envelope removed.

Fig. 4 is a detailed sectional view of part of Fig. 1, showing the shield clip in its normal position.

Referring to Figs. 1 to 3 the numeral I represents a base or header of suitable metal such for example as steel, iron, nickel or similar metal. Preferably, although not necessarily, the header I is formed with a downwardly depending rim 2, and a centrally located exhaust tubulation 3 through which the device may be evacuated in known manner. The header I is provided with a series of perforations, preferably although not necessarily, circularly arranged, through which insulatingly pass the various lead-in and sup- 1937, Serial No. 135,642

port wires 4 to I0 inclusive, for the electrodes of the mount. Preferably, these wires are insulated from the header by glass beads I I which are hermeticaliy sealed into the upper ends of the associated metal eyelets I2, each of these eyelets being in registry with a corresponding perforation in the header and preferably welded thereto. Preferably also the eyelets are of an alloy sold under the trade name Kovar or of an alloy sold under the trade name Fernico. These alloys may be composed substantially of 18% cobalt, 28% nickel and 54% iron and the glass beads may be of any suitable boro-silicate glass such for example one having the following approximate composition: silica, 23% boric oxide, 7% sodium oxide and 5% aluminum. oxide. It will be understood of course that the invention is not limited to these particular materials so long as the glass beads can be sealed in a vacuumtight manner to the header.

Merely for purposes of illustration the invention is shown as embodied in a tube of the triode type comprising any well-known form of indirectly heated cathode I3, a fine wire grid I4, and a tubular metal plate I5. The grid side rods I6, ii are welded or otherwise fastened at their lower ends to the wires 6, 8 while the plate is electrically connected to the lead-in wire 1. Wire I is provided with an upwardly extending offset portion I8 which passes through a bore in the shield member 26 described hereinbelow, the upper end of wire l8 being connectedto the plate I 5. The heater filament 26 has its ends connected to the wires 4, 5 and the cathode sleeve I3 is connected to the wire 9. Preferably there are provided upper and lower insulator discs or spacers 2|, 22 in the form of mica sheets perforated to receive the ends of the cathode sleeve and the various side rods. If desired a flexible extension or extensions may be attached to the disc 2| to engage the inner'face of the metal bulb 23 for the purpose of steadying the upper end of the mount. I

As shown in the drawing, the bulb 23 is in the form of a metal cylinder of iron, steel, nickel or similar metal having a flattened top 24 and pro-- vided at its lower end with a peripheral flange 25 which may be welded or otherwise fastened in a vacuum-tight manner to the member I. As is well-known in the radio tube art it is necessary for various reasons to employ during part of the evacuation process a getter or clean-up agent which can be readily flashed or vaporized at the appropriate time so as to clean-up the residual gases or vapors that remain after the main evacuation takes place. However in flashing this getter it is highly important that it be prevented from depositing to any substantial extent on the glass beads H and thus reducing the insulation of the lead-in wires from the metal header i. For this purpose, there is provided a cylindrical shield 26 preferably, although not necessarily, of ceramic or similar insulating material which is adapted to surround the various lead-in wires. The shield 26 is provided at its upper end with a shoulder 2'! on which is seated the lower end of the plate electrode as shown clearly in Figs. 1 and 4. Preferably the shield is also provided with a series of recesses 28 to accommodate the glass beads H. Since the shield is of insulating material and the header l is of metal, ordinary methods of fastening the shield in place as for example welding, cementing,etc., are not feasible. Therefore in accordance with the present invention the shield is held in place by one or more sub stantially L-shaped metal clips such as clip 29 the bottom 30 of which is welded or otherwise fastened to the header i. In order to accommodate the clips, the shield 26 is provided with notches 3i and in vertical alignment with the notches the wall of shield 26 is provided with slots or grooves 32.

As shown in Figs. 1 and 4, each clip 29 is bent to form' a shoulder 33 which is adapted to engage the bottom of the slot 32 to prevent vertical displacement of the shield. In order to hold the said shield firmly in place the end of clip 23 is bent to a V-shape so that when the tube 23 is fitted over the mount the upper end of the clip is forced inwardly from its normal position as shown in Fig. 4 to the position shown in Fig. l where it lies in the slot 32. The getter material in the form'of a small strip or sheet welded to the inner face of the tube 23 is indicated by the dotted rectangle 34, Fig. 3, and in order to enable the tube 25 to be assembled over the shield without disturbing the getter strip, the shield is provided with a flat 35.

It will be understood of course that the getter instead of being in the form of a fiat metal strip or tab, may be in the form of a pellet enclosed in a suitable getter cup or capsule which is welded to the inside face of bulb 23. Similarly the getter may be in the form. of a powder compressed into a suitable pocket or depression on the inner face of the bulb as is well-known in the art; In order to flash or vaporize the getter, heat is applied locally, as for example by a small torch, to the exterior of bulb 23 adjacent the 10- cation of the getter, and if desired a suitable mark or indentation may be employed to indicate, from the exterior of the bulb, the getter location.

The assembly of the various elements of the tube is believed to be obvious from the foregoing and is in general as follows. The cathode and grid electrodes are assembled on the mica members 2!, 22 which are held in place on the grid side rods by suitable metal eyelets or the like. The grid side rods are welded to the corresponding lead-in wires 6, 8; the heater filament is connected to its lead-in wires 4, 5; and the cathode is connected to its lead-in wire 9. The shield 26 is then assembled in place and forced downwardly to cause the shoulders 33 of clips 29 to latch in the corresponding recesses 32. The plate 15 is then assembled in the end of shield 26 and rests on the shoulder 21 being held against upward movement by wire l8 which is fastened to the plate. The bulb 23 with the getter material 34 attached thereto is then assembled over the mount and forced downwardly causing the upper free ends of the clips 29 to enter the corresponding slots 32. The flange 23 is then welded to header I, and the completed tube is evacuated through tubulation 3 and heat treated and otherwise subjected to the customary pumping schedule. At the appropriate interval of the said.

schedule the flame of a small torch is applied instantaneously against the bulb 23 adjacent the getter 34 causing the latter to be flashed. Because of the shield 26, the vaporized getter material is substantially prevented from depositing on the glass beads II, or on the micas 2|, 22. After the tube has been completely evacuated and processed, the tubulation 3 is sealed off and any well-known form of prong or contact base is attached to the header l.

While certain specific materials and arrangement of parts have been disclosed herein, it will be understood that various changes and modifications may be made without departing from the spirit and scope of the invention.

What I claim is:

1. An electric discharge tube comprising an envelope consisting of a tubular member hermetically sealed to a base member, a tube mount carried by said base member, lead -in wires for said mount and sealed into said base member,

getter material carried on the inner face of said tubular member, and an insulating shield within the envelope for protecting said lead-in wires and seals from the vaporized getter material.

2. An electric discharge tube comprising an envelope consisting of a tubular member hermetically sealed to a base member, a tube mount carried by said base member, lead-in wires for said mount insulatingly sealed into said base member, a cylindrical shield of ceramic insulating material within the envelope surrounding said lead-in wires, and means flexibly latching with said shield to fasten said shield to said base member.

3. In a device of the character described the combination of a tube mount, a metal base member supporting said mount, lead-in wires insulatingly sealed into said base member, a curved shield of insulating material for protecting said lead-in wires and seals from vaporized getter material, and a flexible metal clip carried by said base member and latching with said shield.

4. In a device of the character described the combination of a tube mount, a metal base member supporting said mount, lead-in wires insulatingly sealed into said base member, a ceramic getter shield surrounding said lead-in wires, a metal clip fastened at its lower end to said base member, a shoulder formed on the wall of said shield, said clip being bent intermediate its ends to form a shoulder arranged to latch over the shoulder on the shield.

5. In a device of the character described the combination of a tube mount, a metal base member supporting said mount, lead-in wires insulatingly sealed into said base member, a ceramic getter shield for said lead-in wires and their seals, a slot in the wall of said shield, a flexible metal clip having an offset portion lying in said slot and engaging said shoulder to hold said shield firmly against said base member.

6. A device according to claim 5 in which the said shield is cylindrical and supports a tubular plate electrode at its upper end.

'7. In a device of the character described the combination of a metal base member, a tube mount carried by said base member, a curved getter shield of insulating material disposed around the vertical axis of the mount, a shoulder formed on said shield, a tubular bulb sealed to said base member, and at least one metal clip having a pair of oiisets one engaging said shoulder to prevent vertical movement of said shield and the other engaging the inside of said tubular bulb to space said shield from said bulb.

8. In a device of the character described the combination of a metal header, a plurality of glass beads sealed tosaid header, a wire sealed through each bead, a tube mount carried by said header and having its electrodes connected to said wires, a metal bulb enclosing said mount and hermetically sealed to said header, an insulating getter shield surrounding said wires, a plurality of recesses in said shield into which said beads partially extend, a plurality 01 slots in the shield wall, a corresponding plurality of flexible wire clips each fastened to said header, each clip having a substantially V-shaped end with the apex of the V engaging the inner face of the bulb to force the end of the clip into a corresponding slot in said shield.

9. A device according to claim 8 in which the shield is of ceramic material spaced from the wall of the bulb, and a quantity of getter material is located between the bulb wall and the shield.

10. A getter shield for a metal envelope radio tube comprising a tubular ceramicmember hav-. ing at least one slot in its outer faceto receive a wire clip.

11. A getter shield according to claim 10 in which the upper end of the ceramic member is shouldered to receive a tubular electrode.

RICHARD G. BENNEI'I.

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