US2121591A - Grid glow tube with zero temperature effect - Google Patents

Description

R K. GESSFORD ET AL GEID GLOW TUBE WITH ZERO TEMPERATURE EFEEcT' Filed Jan. 10, 1936 ENVENTORs. Dewey D; Know/e5 and 19055 K Gressford.

WITNESSES: WMM

Patented June 21, 1938 UNITED STATES PATENT OFFICE GRID! cnovv TUBE WITH ZERO TEMPERA- TUBE EFFECT Application January 10, 1936, Serial 'No. 58,526

' 7 Claims.

This invention relates to gas filled discharge 7 devices of the sort used to rectify currents and for grid control of currents.

It is an object of this invention to increase the life of tubes and particularly to avoid the limitation upon the life of the tube which can be attributed to the clean-up action of the discharge.

It is a further object of this invention to so 16 arrange the electrodes that no discharge will occur through the parts of the tube adjacent to the glass.

It is a further object of this invention to provide a shield surrounding the dischargepath and 1 5' acting to prevent ionization of the gas outside of the shield. 9

It is a iurther'object'oi thisinvention toprovide a shield in the form of a'cylinder surrounding the anode and cathode and having a partition separating the anode and the cathode.

It is a further object of this invention to-prO- vide such a grid with the part next to the anode imperforate, and the remainder of the'grid containing many perforations. V 1

It is a further object of this invention to provide a structure of the class described in which the cathode is situated between the partition across the cylinder and a radiation shield supported from the press.

It is a further object of this invention to provide an atmosphere free from mercury in which the discharge occurs. 5

It is a further object of this invention to provide in a gas-filled tube free from mercury a correctly chosen pressure whereby sputtering'is prevented and yet grid control is permitted; In a tube of this sort with the pressure so chosen,the life of the tube is greatly enhanced.

It is a further object of this invention to pro- 40 duce a device of the class describedin which the tube characteristics shall be constant at all ordinary temperatures. 1

It is a further object of this invention to provide a discharge tube filled with helium.

i It is a further object of this invention to provide a structure whereby the gas pressure can be increased above that used in conventional structures still maintaining the control voltage limit and giving lower tube drop, and increased life.

Other objects of the invention and details of the'structure will be apparent from the following description and the drawing, in'which Figure 1 is a vertical sectional view through the device, and

Fig.2 isla similar view,.the section being taken in a vertical plane at right angles to that of Fi 1.

The device comprises a glass envelope I having a press 2 in which are several standards. The specific illustration discloses three of these stand- 5' ards although more or less may be provided. The upper partof the press has a flange 4 which affords a lengthy leakage path for any leakage across the press to the leads. I}

The cathode 1 consists of a coiled metallic rib- 10 bon coated with emissive oxides. It is supported between two of the standards, 8 and 9, which extend through the press to external conductors. These standards are welded to the ends of the w ribbon and form the conductors to the heating 15 circuit. The standard 9 is connected by means of a welded sleeve H] to a radiation shield II. The standards 8 and 9 extendthroughperforations in the shield l I, the sleeve Ill being welded to the radiation shield H at one of these perforations. 20 The radiation shield is thus maintained at the potential of one end of the cathode.

The anode is supported at the other endof the envelope by means of a press l5 through which a standard It extends. The standard 16 is sur- 25 rounded by a glass skirt H which is continuous with the press I5 and forms a lengthy path preventing leakage'to or from the anode l8. External of the envelope the standard It is united with a cap I9 affording convenient connection 30 means for the anode circuit.

The anode I8, the cathode 1 and the radiation shield l l are surrounded by a cylindrical grid or shield 20. A partition 2! is secured across the cylinder 20 between the anode l8 and the cathode 35 l. The partition 2| is foraminate, the foramini having diameters of about one-tenth of an inch. For certain purposes it may be desirable to make the cylinder 20 foraminate also, although a construction in which the portion above the partition 40 2| is devoid of perforations, or alternatively in Which the entire cylinder '20 is imperforate is within the scope of my invention.

No mercury is left in this tube when it is finished. It is filled with a noble gas of light 45 the anode l8 and the cathode, a discharge is set up which extends from the anode 18 through the perforations in the grid to the cathode 1. No discharge occurs in the space outside of the grid, although such discharge can occur with a rid foraminate over its whole extent. When this tube is operating, a glow may be observed in the space between anode and cathode, but it may be seen that no such'gloW occurs outside of the grid 20.

The reason for this we are not at present able to state with certainty, but it is our belief that l the metallic body 20, in addition to its action as a grid, acts also to absorb whatever ions collide with it and thus prevent the formation of an are outside of it. The charges thus introduced into the cylinder 20 are conducted by the connector 23 and over the lead 24 to whatever external connection is provided. For many purposes, the external connection is to one end of the cathode. We believe that the electrons from the cathode 1 will not penetrate the openings in the grid in sufiicient number to set up ionization in the gas except in the line between the cathode and the anode where the electrons possess a high velocity. The ions which they thus create by ionization of the gas neutralize the space charge and provide ready formation for an are through the holes in the partition 2|, but only a little field from the anode l8 extends into the space exterior to the cylinder 20 and, therefore, no such velocity can be given to the electrons which tend to emerge from the cylinder. We do not wish to be limited by this explanation because we are unable as yet to be sure why the discharge does not occur outside of the cylinder 20.

When the gaseous discharge tubes known heretofore are working, the discharge produces a diminution in the pressure of the gas. When this effect has proceeded so far that not sufficient gas remains to supply ions, ionization ceases and the life of the tube is terminated. We believe that this effect of the discharge upon the gas is most rapid when the discharge takes place near the glass. We have observed but are not yet able to explain that the clean-up effect of the discharge upon the gas does not occur when the discharge does not contact the glass of the envelope. We, therefore, have provided that the cylinder 20 extends beyond the anode l8 into close proximity with the envelope I. The anode I8 is unable, therefore, to have an arc extending around the end of the cylinder 20 and through the holes in the cylinder 28 to the oathode 1. There being no discharge in proximity to the glass, there is little or no clean-up effect noticed. The tube, therefore, can last indefinitely.

When desired the shield is connected through the lead 24 to an external source of potential.

The potential of the grid may be'varied according to any desired flow. One well known flow which we have found useful is to keep the grid sufiiciently negative to prevent an are forming until a predetermined point in the cycle of al ternating potential is reached and then permit it to become sufiiciently positive to permit an arc to form. The are will then continue until the anode potential has become zero.

If the tube be filled with mercury-free gas the pressure may be so high that no potential on the grid will prevent the are from forming. If the gas pressure be too low sputtering at the cathode will be so rapid that the life of the tube is shortened thereby. We have found with helium that a pressure of 1.75 mm. of mercury gives good results with the grid herein described. If a higher pressure of helium is used the control by the grid at 750volts on the anode is lost.

We do not desire that the specific description and illustration of one form of our device should limit us to that specific form, but we recognize that many modifications will occur to those 7 skilled in the art. No limitation is intended exode, the portion of the cylinder on the anode side of said partition being imperforate and all the rest of said grid being foraminate.

. 2. In a gaseous discharge device, an envelope, a cathode and an anode therein, a cylindrical grid surrounding said anode and cathode and a perforated partition across said grid separating said anode and cathode, the gaseous atmosphere within said envelope consisting of helium at a pressure of the order-of 1.75 mm. mercury.

3. In a gaseous discharge device, an envelope, a cathode and an anode therein, a cylindrical grid surroundingsaid electrodes and electrically separate therefrom and a perforated partition across said grid separating said anode and cathode, the cylindrical portion of the grid being imperforate and extending past the anode into close proximity with the glass.

4. A gas discharge device comprising an envelope containing an anode and a cathode, a filling of a gas which is non-liquefiable at ordinary room temperature and pressure, the pressure of said gas being of the order of 0.4 mm. to 1.75 mm. mercury, and a conductive member surrounding said anode and cathode and extending into close proximity to said envelope in the region of the anode, said-member having a perforated partition extending across its interior to separate said cathode from said anode. I 5. A gas discharge device comprising an envelope containing an anode and a cathode, a filling of helium at a pressure of the order of 1.75 mm. mercury, and a conductive member surrounding said anode and cathode and extending into close proximity to said envelope in the region of the anode, said member having a perforated partition extending across its interior to separate said cathode from said anode.

6. In a gas discharge device, an anode, a cathode, and a conductive member surrounding said anode and cathode and having a perforate portion transverse to the region between them, said member being foraminate throughout the portion nearest thecathode and imperforate near the anode, the imperforate portion extending beyond the' anode.

7. In a gas discharge device, an envelope, an anode, a cathode, and a conductive member surrounding said anode and cathode and having a perforate portion transverse to the region between them, said member being foraminate throughout the portion nearest the cathode and imperforate near the anode, the imperforate portion extending beyond the anode into close proximity to the envelope.

ROSS K. GESSFORD. DEWEY D. KNOWLES.

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