US2103031A - Electric gaseous discharge device - Google Patents

Description

Dec. 21; 1937.

T. E. FOULKE ELECTRIC GASEOUS DISCHARGE DEVICE Filed Feb. 8; 1935 INVENTOR Ted E.Fou.lke.

B i I I ATTORNEY Patented Dec. 21, 1937 UNITED STATES ELECTRIC GASEOUS DISCHARGE DEVICE Ted E. Foulke, Nutley, N. J assignor to General Electric Vapor Lamp Company, Hoboken, N. J., a corporation of New Jersey Application February 8, 1935, Serial No. 5,670

3 Claims.

The present invention relates to electric gaseous discharge devices, and particularly to discharge devices of the cathode glow type.

A particular object of the invention is to provide a cathode glow device having extremely constant electrical characteristics. Another object of the invention is to provide a cathode glow device which may be produced in quantity without any appreciable variation in the electrical characteristics of the individual devices. Still other objects and advantages of the invention will appear from the following detailed specification, or from an inspection of the accompanying drawing.

The invention consists in a device having the new and novel characteristics hereinafter set forth and claimed. V f

Electric gaseous discharge devices of the cathode glow type have many characteristics which especially adapt them to use as voltage regulators and oscillators. For these particular uses, however, and particularly Where the device is to be used as an oscillator for electrical musical instruments and the like, or in testing devices, it is absolutely essential that the electrical constants should be stable'in operation throughout the life of the device. It 'isalso essential that these characteristics should be reproducible, so that mass production may be achieved without the necessity of large circuit adjustments to compensate for variations in these characteristics. Up to the present time no device has been available which completely met these requirements. Thus when attempts were made to use various cathode glow devices as an oscillator for an electrical organ it was found that the pitch of the note produced wavered and varied in a manner which completely ruined the musical effect. In addition it was difficult to obtain any two devices which might be interchanged without major changes in the circuit, due to the diificulty of reproducing these devices.

After considerable research work on this problem applicant discovered that the desired result of both stability and reproducibility is attainedv by use of a novel electrode structure of his invention. According to this invention the cathode is made in the form of a tubular sleeve which is positioned about the anode, with a Vshaped indentation which aproaches said anode. Thiscathode "is activated on the inner surface with a substance erably volatilized within the device in order to produce and maintain the desired gas purity. With this novel construction it has been found that the discharge is always initiated between the apex of the V and the anode, this breakdown being particularly low due to the sharpness of the V. By controlling this gap the breakdown potential is made easily reproducible. After the discharge is initiated it travels along the sides of the V and centers at the angles formed between this V and the remainder of the cathode. This eliminates the moving about of the discharge on the cathode which occurs in any of the prior art devices, and thus avoids the instability which has heretofore caused the wavering in the frequency of the discharge. Even with this new geometry, however, the greatest stability of the discharge is only produced when the entire inner surface of the cathode is coated with the substance of low work function, even though the glow is limited to the surface near the V portion thereof. This is believed to be due at least in part to the fact that this active material cleans up immediately any gas evolved during operation of the device and thus maintains the gas and the discharge supporting portion of the cathode in an ideal condition.

For the purpose of illustrating my invention I have shown a preferred embodiment thereof in the accompanying drawing, in which Fig. 1 is an elevational view, in part cut away,

of a cathode glow device especially adapted for As shown in the drawing my novel device has a sealed envelope I of glass or any other suitable material with a reentrant stem 2 through which are sealed the inleads 3 and 4. A tubular anode 5 is welded to the inner end of the inlead 3, said anode being adapted to retain a piece of magnesium 6, as shown in Fig. 3, which is volatilized during the manufacture of the lamp. This anode is conveniently made of nickel plated iron, since it has been found that such an. electrode is not only easily heated by a high frequency field but is also easily freed of any oxide coating. The inlead 4 is weldedto a support wire 1 which is in turn Welded to the cathode 8. Said cathode is preferably formed of sheet nickel which is bent and welded to form a cylinder with a v-shaped indentation in one side thereof. In practice this cylinder has been made one fourth inch in length and the same in diameter, and the V-shaped indentation has been formed with legs approximately three sixteenths of an inch in length and with approximately a right angle therebetween. The apex of this V is carefully located with respect to the anode 5, a gap of the order of 0.5 to 1.0 m. in. being left therebetween in practice. The entire inside surface of said cylinder ispreferably coated with a substance having a low work function, such as disclosed in my Patent No. 1,965,589, granted July 10, 1934, while the outer surface of said cylinder is preferably coated with finely divided aluminum, since this coating prevents the creeping of the glow onto this exterior surface, as disclosed in my Patent No. 1,965,586,

granted July 10, 1934, and also serves, after being heated, as a good getter which cleans up gaseous impurities in the device.

The envelope l is filled with a suitable gaseous atmosphere, such as one or more of the rare gases. In practice I prefer to use a mixture of neon with approximately 0.4% argon at a pressure of the order of 30 m. m. of mercury, since this mixture and pressure have been found to give an exceptionally good stability to the electrical characteristics of the device, and also to give a low breakdown potential. This increase in stability is partly due to the fact that this gas mixture operates in a unique manner to permit the uniform activation of the entire cathode sur- 7 face, so that the cathode glow will spread evenly thereover. This in turn results in the smooth operation of the device with variation in current, without the sudden and erratic changes which would occur if the cathode were not thus uniformly conditioned. This is probably due to the fact that although the average current when the device is used as an oscillator is less than one milliampere the peak currents momentarily produced by condenser discharge in this class of service are relatively large. If the entire surface is not uniformly activated erratic behavior of the device results. This variable is entirely eliminated in my novel device, however, with the re sult that a sustained note of constant pitch is always produced when the device is usedin a 'musical instrument, for example.

In the preferred method of manufacture the electrode structure is assembled as shown and the cathode coated on the inner surface with a mixture of the carbonates of barium and strontium while the outer surface is coatedwith powdered aluminum, a suitable binder, such as nitrocellulose, being used where desired. This assembly is then sealed into the envelope I and the envelope exhausted withinan oven. The metal parts of the electrode assembly are then heated by means of an induction furnace to degas them and the cathode 8 is thenfurther heated-to a temperature suflicient'to reduce the binder and The i also to reduce the carbonates to the oxides. anode 5 is also heated during this process, but due. to its greater thermal capacity and lower linkage with the high frequency field produced by 'the induction furnace the magnesium 6 is not volatilized untilrafter the other gas evolving operations are virtually completed. The volatilized magnesium then condenses over the inner surface of the envelope I and thus has-an extended surface which is extremely effective in cl'eaningi' up oxygen and any other gaseous impurities which are evolved during the subsequent treat ment and operation of the device. The'desired the purpose intended, such as an oscillator lamp.

When so constructed my device has a breakdown potential of the order of '82 volts D. C. and a discharge maintaining potential of the order of 68-70 volts D. C. More important, however, these devices are readily reproducible in mass production with only extremely small variations therein. Likewise the operation of eachindividual lamp is exceedingly'stable. Thus the discharge always starts to the apex of the V on the cathode at the same potential and then spreads along the 'sides of this V, and centers in operation "at the corners betweenthe sides of the V and the .re-

.mainder of the cylinder forming'the cathode 8. 7 As a result of this stability of the glow discharge the frequency generated by this device when connected in a suitable circuit as an oscillator is absolutely constant, so that it is the first gaseous discharge device to win approval for use as an oscillator in devices having the exacting requirements'of a musical instrument, for example.

In general the deviceis used without a base since it has been found that any of the usual bases introduce a variable leakage resistance which materially impairs the operation of the device.

While I have illustrated'my invention by'reference to a specific embodiment thereof which has provedto be entirely successful, it is to be understood that it is not limited thereto, but that various omissions, substitutions and changes, within the scope of the appended claims, may be made therein without departing from thespirit of my invention.

' I claim as my invention:

1. An electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere, and an anodeand a cathode within said envelope, said cathode being in the form of a cylinder surrounding :said anode with a V'- shaped indentation therein whose apex is closer to said anode than the remainder'of said cylinder, the inner surface of said cylinder being coated with a substance'having a low work function.

2. An electric gaseousdischarge device comprising a sealed envelope containing a gaseous atmosphere, an anode and a cathode within said envelope, said cathodebeing in the form of a cylinder surrounding said anode with a V-shaped indentation extending closer to said anode than the remainder of said cylinder, a coating "of a substance having a low work functionon the inner surface of said cylinder, and an extended area of a reducing agent within said envelope.

3. An electric gaseous discharge device comprising a sealed envelope containing a mixture of neon with a small quantity of argon at a pressureof the order of 30 m. m. of mercury, and-an anode and a cathode within said envelope, said cathode being in the form of a sleeve surrounding saidfanode witha V-shaped indentation therein whose apex approaches said anode.

' TED E. FOULKE.

Images