US2007938A - Thermionic amplifier - Google Patents

Description

July 9, H935. s RUBEN THERMIQNIG AMPLIFIER Filed Aug. 23, 1930 2 Sheets-Sheet l m T N E V m l lil'l mm July 9, W35. RUBEN A 2,U7,938

THERMIONIC AMPLIFIER Filed Aug. 25, 1930 2 Sheets-Sheet 2 INVENTOR 5/7/1011 foam ATTORNEY Patented July 9, 1935 K I w UNITED STATES f PATENT OFFICE Samuel Ruben, New Rochelle) N. Y., assignor to Susan Lamp Company, Newark,' N. J., a corporation of Delaware Application August 23, 1930; serial No. 477,304 sciaims. (01. 250-275) This invention relates to thermionic amplifiers end of the other elements insulatedly with respect or relays and particularly to that type of device. to eachother. which depends for operation on the ionization of The grid l3 may comprise a helical coil 21 of a gas. fine'wire such as molybdenum wire which may One of the objects or the invention is to pro-' w d d t tw supp t r ds 22 and Th 5 vide an amplifier which will carry relatively large diameter of the coil may be somewhat l r er than amounts of plate c rre t, the-element l2 so that itmaybe spaced from the Anotheri'object of the invention is to'provide element: but. mounted concentrically therewith.

an amplifier which will operate at relatively low upp r r d 2 m be connected at its l w r 1O 'p1ate voltage. l end to a relatively short support rod 24 which I Other objects of the invention and objects rey be Sealed n the press I] W e the p end lating' particularly to the construction and as- 0f e supp fi d 3 may be Welded a 0011- sembly of the various parts will be apparent as necting ro 25 Which m y extend y and the description of the invention proceeds. then be bent downwardly to be sealed into the 5 The invention is illustrated in the accompanybead l9. 7 l i ing drawings in which: i I The anode Mmay be formed of two semi-cylin- Fig. 1 is a perspective View partly in section 0 1 drical pl havin flan es-26 r y x ndin my improved amplifier t b atthe sides thereof which may be welded together Fig. 2 is a longitudinal sectional view, some to f rm acomplete cylindrieal anode which is what enlarged, of one end of the element or Pr f y l r r han h rid so as to e paced. 20 cathode shown in the construction of Fig. 1; i 1 from it but mountedconcentrically with the grid Fig. 3 is a circuit diagram showing the use of d hOdG- The fl y be p ovided the amplifier; and i with grooves 21' adjacent the outer edges to re- Fig. 4 is a front sectional view of amodified iv th pp rtr whi h m y be sealed 5. form of t device; inithe press ll at'their lower ends and may extend 5 Referring now more specifically to the drawings upwardlythrollghvthevgroovfis 27 being welded t the embodiment of the invention shown in Fig. 1 theflafiges The rods 23 y also be bent comprises an envelope lomounted onvthe usual a kwar ly ab ve th anode M and wnw rdly Y press l I which may be formed integral with the againwhere the e d ay b Sealedill the be d 9- 30 envelope to support the various elements of the nthiS ma the Ca grid, and ode are 30 device; The elements comprise a cathode I2, a: s ur y d n h pr ss H i spa d r lagrid I3, and ananode It. The cathode may comtion wi h other and ri y so as to avoid prise a coil l5 of resistance wire such as tungsten; anymovementwithiespect o each er. molybdenum, tantalum, or nichrome, which may M'I'he envelope. may be filled :at a pressure of beclosely wound to form a concentrated filament about 200 with an ionizable gas and prefer- 5 coil as indicated in Fig. 2. The outer. surface of ably one of the. monatomi'cl gases such as argon, the coil may be coated with electron emitting ma- 1161111111.,118011, krypton,- or xenon. terial I6 which may beany of the materials com- After r the elements are mounted as shown in monly used for that purpose such as the oxides Fig. lwwith. the press formed integral with the 40 of the alkali metal group or mixtures of suchv envelopeythe envelope may be connected in the 4 oxides; Such material may be'mixed'with a suit-. usual mannerto-fan exhaust pump and an oven able binder and applied to the outer surface of placedoveritto raise the temperature thereof to the coil by any desired means such as a brush. between 350 to400i C. or as high a temperature and then dried in position. as the parts will stand without injury. This The coil l5 may be supported atitslowcr end drivesroutoccluded gases from the various parts 5 upon a short support rod I! whichmay be sealed and the exhaust :pump withdraws the gases as in the press I I while the upper end of the coil may they are driven out. During this time a current be supported upon a rod I8 whichmay be bent may be run through the element 12 to raise the rearwardly, downwardly, and inwardly again temperature to approximately 600 C. to drive where it may also be sealed in the pre'ss H; A out some of the occluded gases. This treatment 5 glass bead 19 may be attached to the rod in back is continued until no more gas appears in. the of the element !2 either by being sealed on to tube as is evidenced by the lack of fluorescence the support rod or having a short angular support whenhigh tension current is directed against the rod 213 welded to the support rod and seal'ed in wallsof the bulb from an induction coil. A high the bead. This head is for supporting the upper: vacuumrof about:.5 micron is preferably obtained.

The current through the filament may then be increased so that the temperature is slowly raised until it is about 800 C. with a bright red color. This heating tends to drive out the binder in the electron emitting material and other occluded gases which have not already been released, the vacuum pump drawing the gases out as they are driven from the various parts. When no more gases are found in the bulb the oven may be raised and the filament heated to slightly less than 1200 0., the pump being connected all this time to remove any gases driven oil? and maintain the vacuum.

The pump may then be shut ofi and the filament current turned off and a slight amount of an inert gas such as neon gas at about /2 mm. pressure may be admitted to the bulb and the filament current turned on and gradually increased. Spots of localized discharge will then.

appear having a reddish color and these spots will gradually spread until a diffused glow completely fills the bulb. This process appears to activate the electron emitting coating and may be maintained until the discharge is uniform throughout the entire bulb which usually takes less than ten minutes. During this time the current on the filament should not be raised too high so that the coating will not be destroyed or thrown off from the filament. If white discharge spots appear on the filament or support rod it is an indication that there are more gases or vapors in the bulb and the bulb should again be exhausted and the whole process of activation repeated.

When the activation is completed the filament temperature may be raised to about 1400 C. for a moment and then the vacuum pump connected again to remove any undesirable gases which may have been thrown off during the activation process.

When the high vacuum is again obtained the filament circuit may be disconnected, the pump turned off, and about 50 mm. of neon gas may be admitted to the bulb followed by about 150 mm.

i of argon. The bulb may then be sealed off and cleaned up by flashing magnesium therein.

Magnesium may be introduced into the bulb by attaching it to a small container 30 which may be connected by means of a wire 3| to one A of the support rods as the support rod 28 in the tube. When the magnesium has been flashed the tube is ready for use.

When current is run through the element supports the emission of electrons therefrom appear to ionize the region in the vicinity thereof thus producing a conducting path from oneend of the element to the other and a gaseous discharge appears around the element like a halo. The size of this discharge or halo may be controlled by the grid I3 as when it has a negative potential the discharge tends to collapse while when it has a positive potential the area of the discharge tends to increase. As the region of discharge forms a conducting path through the gas it will conducta large amount of current between the cathode and anode when the discharge is large enough to include the anode. Hence, a large amount of plate current may be modulated by a slight variation of potential on the grid.

The amplifier may beused in the usual manner as indicated in Fig. 3 where the grid 3 is connected through an input transformer 32 to the negative side of the A battery 33 which may be connected through a suitable rheostat 34 to the cathode l2. The anode l4 may be connected through the output transformer 35 to the positive side of a B battery 36.

Due to the conducting path between the anode and cathode when the discharge includes the two the tube will carry a large amount of plate current. It is necessary however to have sufficient voltage on the cathode to give a potential drop along the surface to ionize the gas in the tube. The voltage should be at least thirty volts for best results.

It may be desirable to have the device operetc to control a local circuit which is entirely independent of the cathode and grid and if so the construction shown in Fig. 4 may be used. Here a cathode 37 may be supported upon a short support rod 38 at the lower end thereof which may be sealed in the press 39 while the upper end may be supported on a rod 48 which may be bent rearwardly and downwardly and inwardly again where it may be sealed in the press 39 similarly to the rod l8 as shown in Fig. 1. A grid 4| may be formed similarly to the grid E3 of Fig. l and may be supported at its lower end by means of the support rod 42 sealed in the press 39 and at its upper end by means of the rod 43 which may extend rearwardly and be bent downwardly where it may be sealed in a bead 44 secured to the support rod 45 in a manner similar to the bead I9 of Fig. 1.

A pair of cylindrical electrodes 45 and 45 may be positioned around the grid 4| but spaced longitudinally as indicated. The electrode 45 may be formed of a strip of metal with a flange 41 extending radially from one side thereof. This flange may be welded to a support rod 48 which may be sealed in the press 39 and may extend upwardly beyond the upper end of the electrode 45 where it may be connected to a short angular support rod 49 which may be sealed in the bead 44. In like manner the electrode 4-6 may have a radially extending flange 50 which may extend in the opposite direction from the fiange 4i and may be welded to a support rod which may extend downwardly spaced from the electrode 45 and may be sealed in the press 39. The upper end of the support rod 5| may be welded to a short angular support rod 52 which may be bent rearwardly 221d downwardly and may be sealed in the bead A leading-in wire 53 may be connected to the support rod 48 while another leading-in wire 54 may be connected to the support rod 5| thus connecting the electrodes 45 and 46 respectively. The leading-in wires 55 and 56 may be connected to the rods 48 and 50 respectively to form the connection for the cathode while a leading-in wire 5'! may be connected to the grid support rod 52.

If then the grid connector 51 is connected by means of a wire 58 to an input circuit 59, the other side of which is connected by means of a wire 60 to the negative side of an A battery 6| which may be connected across the cathode terminals 55 and 56 by the wires 52 and 63 respectively, then a modulation of the input circuit 59 will cause a change in the conductivity between the two electrodes 45 and 46. Hence, if these electrodes are connected in a local circuit by connecting the leads 53 and 54 by wires 64 and 65 including a battery 66 and a translating device 61 current will flow in the local circuit and through the translating device as the conducting path between the electrodes 45 and 46 changes.

While I have shown a cathode which is comprised of a concentrated coil of wire other types of cathodes may be used as for instance a single straight wire coated with electron emitting material although I prefer to use a large potential drop between points on the emitting surface, if possible, and hence I prefer to use a coil for this purpose. Also while the coating of electron emitting material has been shown as a solid coating on the surface of the coil it will be evident that the individual turns of the coil may be coated separately if desired.

While I have described the tube as being filled with neon and argon gas other gases may be used such as those mentioned above which may be preferable because of their monatomic structure. If desired also the conductivity of the gas may be increased by adding a small amount of metal vapor such as the vapors of mercury, rubidium, or caesium and these metal vapors may be introduced into the bulb by providing a small quantity of a salt of the desired metal, such as a chloride, upon the container 30 adjacent the magnesium. When the magnesium is flashed it reacts with the salt liberating the metal which condenses on the inner wall of the bulb to be evaporated again when the tube is operated.

Also while a certain specific structure has been shown and described it is to be understood that this is for the purposes of illustration and that the amplifier is intended to include any structure in which a current between a cathode and an anode is modulated by a grid and which makes use of the ionization of the gas in the vicinity of a continuous conductor cathode.

Many other modifications of the invention may be resorted to without departing from the spirit thereof, and I do not therefore desireto limit myself to what has been shown and described except as such limitations occur in the appended claims.

What I claim is:

1. An amplifier comprising an electron emitting cathode, a grid spaced from said cathode, an anode spaced from said grid, and an ionizable gas surrounding said cathode, grid, and anode, and comprising a mixture of argon and neon gas and having a pressure of approximately 200 mm. of mercury, the breakdown potential of said gas per unit length of the cathode when subjected to electron bombardment being less than the potential per unit length necessary to raise the cathode to operating electron emitting temperature, and an envelope including said cathode, grid, anode, and gas.

2. An amplifier comprising an electron emitting cathode, a grid spaced from said cathode, an anode spaced from said grid, and an ionizable gas surrounding said cathode, anode, and grid, and comprising approximately 25% of neon and approximately 75% of argon and having a pressure of approximately 200 mm. of mercury.

3. An amplifier comprising a filamentary resistance wire, a coating of electron emitting material upon the surface of said wire, a grid spaced from said wire, an anode spaced from said grid, and an ionizable gas surrounding said wire, grid, and anode, and comprising approximately 25% of neon and 75% of argon and having a pressure of approximately 200 mm. of mercury.

4. An amplifier comprising a filamentary Wire wound in the form of a coil, a coating of electron emitting material upon the surface of said coil, a grid spaced from said coil, an anode spaced from said grid, and an ionizable gas surrounding said coil, grid, and anode, and containing approximately 25% of neon and 75% of argon and having a pressure of approximately 200 mm. of mercury.

5. A relay comprising an electron emitting cathode, a grid spaced from said cathode, a pair of electrodes spaced from said grid, and an ionizable gas surrounding said cathode, grid, and electrodes, and containing argon and neon and having a pressure of approximately 200 mm. of mercury, the breakdown potential of said gas per unit length of the cathode when subjected to electron bombardment being less than the potential per unit length necessary to raise the cathode to operating electron emitting temperature, and an envelope including said cathode, grid, anode, and gas.

SAMUEL RUBEN.

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