US2094675A - Getter for vacuum tubes - Google Patents

Description

Qct. 5, 1937. B. SALZBERG GETTER FOR VACUUM TUBES Filed June 1, 1936 iNVENTOR BERNARD SAL ZBERG ATlORNEY Patented Oct. 5, 1937 UNITED STATES PATENT OFFIQE.

GETTER FOR VACUUM TUBES Delaware Application Junel, 1936, Serial No. 82,862

6 Claims.

This invention relates to vacuum tubes, such as electron discharge devices and the like, and more particularly to such devices evacuated by the aid of chemically active gettering or cleanup agents, which, during manufacture, are vaporized to reduce the pressure of residual gases in the device.

It is common practice to introduce a small quantity of a clean-up or gettering agent, such as one or more active metals, into the envelope of the device by placing a material containing the active metal in a supporting holder or container mounted in the envelope Where it may be heated, for example by high frequency induction, to flash it and discharge into the envelope space the active metal in the form of vapor, This metallic vapor may strike and condense on insulating members and parts of the envelope between energized elements and lead wires in the tube, and cause troublesome leakage currents to flow.

It is an object of my invention to provide a getter for an evacuated envelope which will direct getter vapors to a localized area in the envelope, away from energized elements in the tube, where the vapor may condense.

A further and more specific object of my in- I vention is to provide a getter for an electron discharge device which will project getter vapor in a substantially straight line trajectory from its source toward and on to a surface in the envelope of the device removed from the active elements in the envelope.

A getter assembly constructed according to my invention comprises a getter holder with a chamber to receive a gettering agent such as a pellet and a .constricted outlet channel or passage from the chamber from which getter vapors may be expelled, the assembly being mounted in the envelope with the channel aimed or directed toward a pre-selected area in the envelope. To insure a substantially straight line trajectory of the vapors emanating from the channel, and to prevent their diffusion at the outlet end or nozzle of the channel, the wall of the channel is so constructed that the vapor coming in contact with the wall will be condensed on and retained by the wall. The wall of the channel is preferably made of a material which remains at a lower temperature than the getter vapor during the flashing of the getter. This lower temperature may be conveniently obtained by either forming the inner wall of the channel of a material having poor heat conducting properties or by providing heat radiating means exteriorly of the channel. When the getter pellet is raised to vaporization temperature, the vapor which does not follow a straight line substantially parallel to the axis of the channel, strikes the wall of the channel and is there condensed. Were it not for the low temperature Walls of the channel, the getter vapor would be reflected from one side of the channel to the other and the discharge would scatter, as it would leave the outlet end of the channel at obtuse angles with respect to the axis of the channel.

The specific features of my invention are set forth in the appended claims and preferred embodiments of the device are explained in the following specification and the accompanying drawing in which: a

Figure 1 shows in sectional perspective view an electron discharge device with a getter embodying the characteristic features of my invention,

Figure 2 is a detailed view of one form of a getter assembly constructed in accordance with my invention, and

Figure 3 is a view of another form of my improved getter, embodying the characteristic features of my invention.

In the specific embodiment of my invention illustrated in Figure 1, which shows by way of example an application of my invention to an electron discharge device, I have shown an envelope l of metal or glass, enclosing an electrode assembly 2 with the usual cathode, anode and other electrodes. The envelope is closed at the lower end and has an exhaust tube 3 through which the tube may be mechanically exhausted by vacuum pumps. For cleaning up residual gases after mechanical evacuation of the envelope I employ a getter assembly 4 comprising, according to one embodiment of my invention, a metal holder or tab with a chamber 5 and with an elongated straight channel or outlet passage 6 opening into the envelope space. Getter assembly 4 has been shown by way of example as mounted above the electrode assembly with a supporting bracket or wire 1 to attach the getter tab to the electrode assembly, and with the channel 6 so positioned that its projection describes a small circular area 8 upon the envelope. During exhaust, and after the pressure in the envelope has been reduced to a few microns by mechanical evacuation, the getter tab holder is heated to vaporize the gettering agent contained in the chamber of the getter holder and to drive the required amount of getter vapor into the envelope to clean up residual gases. The tube may out portions and 9 into registry to form chamher 5 with communicating tubular channel 6.

To keep the temperature of the inner wall of channel 6 below the temperature of the getter vapor during the flash, several methods may be employed. One method which has been found particularly convenient is to coat the inner wall of the channel with a material of low heat conductivity. This coating indicated at l i may be a powdered refractory oxide, such as alundum carried in a liquid vehicle, and applied'to the walls of the channel during assembly by dipping or painting with a brush. The leaves of the sheet metal tab are then closed, and preferably sealed along the edges by welding.

If desired the inner wall of channel 6 may be 7 held at a temperature below that of the getter vapor during flashing by providing heat radiating means on the exterior wall of the channel. The exterior wall of the channel may conveniently be coated with any substance having good heat radiating properties, such as carbon and indicated at ii in Figure 3. Other heat radiating means for the channel portion of the getter holder may, if desired, be provided, such as fins pressed out of the sheet metal stock of the getter holder. It has been found convenient to make my getter holder from short lengths of nickel tubing, flattenedas shown in Figure 3, pressed out at its sides to form the getter chamber and channel, and sealed at'itsiends as by welding.

The size and cross-sectional shape of outlet channel 6 may, in accordance with a further feature of my invention, be selectedto'deposit a condensed vapor pattern of any desired shape or configuration upon a surface in the envelope. Channel 6 in Figure 3 has by 'way of example been shown as rectangular in cross-section, which would produce, when mounted as shown in Figure 1, a rectangular pattern on the envelope at 8. This feature of invention is particularly use iulin depositing the active metals of the charge a in chamber 5 upon, for example, an electrode of predetermined shape. If an electron emitting sensitized surface, for example, is desired to be coated upon the envelope wall or upon a rectan gular electrode, the sensitizing material, such as a pellet of caesium or compounds of barium,

would beplaced in chamber'E, evaporated and deposited over the desired area. It is known that many'active metals adapted to reduce gases by the so-called gettering? action may in their active'statc be employed to sensitize electron emitting surfaces.

Whilepreferred embodiments of' my invention have-above been described for maintaining the temperature of the inner wall of channel 6 below that of the getter chamber, it will be obvious to those skilled in the art that many other modifications may be made Without departing from the spirit of my invention. The getter channel may, for example, be lined with or formed in its entirety of a tube of a ceramic material of low heat conducting properties. While high frequency induction has been mentioned for heating the gettering agent to vaporizing temperature, it is within the scope of my invention to provide a directly heated getter within chamber 5, such as an electric heating coil coated with a gettering agent.

Since many modifications of my invention may occur to those skilled in the art without departing from the spirit of my invention, it is desired that my invention be limited only by the terms of the appended claims and by the prior art.

I claim:

1. In combination, an electron discharge device comprising an envelope enclosing an assembly of electrodes heldin cooperating relation by insulating spacers, and means for reducing residual gases in said envelope on exhaust comprising a getter holder, and a gettering agent in a chamber in said holder, said holder having'an outlet channel for getter vapor of a material adapted to remain at a lower temperature upon heating than said agent. 7 r a 1 2. in combination an electron discharge device comprising an envelope, a getter assembly for reducing gas pressures in said envelope comprising a getter holder having a c hamber', and a gettering agent in said chamber, said holder having an outlet channel communicating with said chamber ,to direct getter vapors from said channel to a pro-selected area upon the wall of said envelope, and means for'keeping' the inner wall of said channel cooler upon heating than the vapors of said gettering ag ent. l

3. In combination, an electron discharge device comprising an envelope with enclosed electrodes, means for depositing an active metal coating'of predetermined size and configuration upon a surface in said device comprising a holder with a chamber, a mass of vaporizable active metals in said chamber, a channel communicating with said chamber of a cross-sectional configuration of that of said surface to be coated and directed toward said surface, and means for maintaining the inner wall of said channel at a lower temper- V ature than the vapor produced from said active metals.

4; A getterassembly comprising a getter holder with a chamber, a channel communicating with

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