US1712370A - Electric discharge device - Google Patents

Description

May 7, 1929. w. c. WHITE ELECTRIC DISCHARGE DEVICE Filed April 27, 1926 Inventor m William C.WhLte, 1-

9 Hts Attorney.

Patented May 7, 1929. v

UNITED STATES WILLIAM 0. WHITE, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEO- 1,212,370 PATENT OFFICE.

TRIO COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC DISCHARGE DEVICE.

Application filed April 27, 1926. Serial No. 104,960.

My present invention relates to vacuum devices and more particularly to means for producing and maintaining a high vacuum in thermionic devices. In the operation of thermionic devices or electronic devices operated substantially independent of gas ionization, and particularly in such devices which are commonly known as power tubes and which usually comprise a W hollow metal anode fused or welded to a glass superstructure, it is sometimes difficult to maintain a high vacuum. This difficulty is due to the fact that gases may be more or less continuously evolved from the difi'erent parts 115 of the discharge device, and in some cases, as where glass issealed to metal, very slow air leaks sometimes develop.

The forces producing gas effects in a tube are roughly proportional to the power involved, and any overload or voltage transient is particularly likely to cause a tube to evolve gas. The gassing effect is cumulative, and although the first gassing may be small and apparently unimportant, the small amount of gas evolved makes the tube even more susceptible to. overload with the result that very soon the tube may evolve gas at a relativelyhigh rate. At such times the tube becomes unfit for use and is discarded, destroyed or returned for a complete reexhaustion.

According to the present invention a." getter bulb is employed to'produce and to maintain the vacuum in a thermionic device at or below a predetermined'pressure. In carrying my invention into effect a bulb or tube of approximately the size of an ordinary watt incandescent lamp is mounted on a thermionic device of the power type. The bulb is provided with a material which maybe vaporized at will as gas accumulates within the discharge device, and is connected to the power device by means of a passageway which is short, and wide enough to permit the getter material in the-bulb to efiectively clean up the gases in the discharge device.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the'appended claims. My invention itself, however, both as to its organization and method of operation will best be understood from reference to the following specification taken in connection with the accompanying drawin in which Fig. 1

represents a view partly bro en away of a getter tube or bulb employed to maintain the vactend through uum in a discharge device; Fig. 2 shows in elevation the metal to be evaporated and the holder therefor, the latter being partly broken away; Fig. 3 is an elevation of an electric discharge device of the power type with a getter bulb mounted thereon; Figs. 4 and 5 show circuit arrangements for automatically controlling the operation of the getter bulb.

Referring to the drawing, I have indicated at 1 the anode member of a power tube 2, in the present instance, a pliotron, although the type of tube employed is immaterial so far as the invention is concerned. A glass sleeve 3 having a reentrant portion 4 is connected to anode 1 by means of the usual metal seal 5. A filamentary electrode, not shown, is mounted within anode 1 and is provided with a pair of leads 6.

Adjacent the upper end of sleeve 3, is a getter bulb of approximately the size of the ordinary 25 watt incandescent lamp. The getter bulb comprises a container 7 connected by a relatively short and wide extension 8 with the interior of the discharge device 2. Mountof molybdenum or other suitable material and within'which is placed a suitable vaporizable material, for example, an alkaline earth metal, which in the vapor state or in the form of" a film will energetically combine with gases. Conveniently a piece of ma esium coated calcium wire 12is used. The en s of the container or holder 11 are provided with cars 13 which are bent over to thereby retain the getter metal in position in the holder. A filamentary conductor 14, which is made of tungsten, surrounds the holder 11 and is connected to a pair of nickel or molybdenum leads 15. The portions of leads 15 and wire 9 whlch exhihe glass press 16 may, if lead glass is used, made of Dumet wire.

The discharge device 2 is evacuated. in any manner desired until a predetermined pressure is obtained. After the device has operated for some time, gas may be evolved,

either from the parts of the discharge device itself, or a certain amount of gas may be introduced by leakage. If, at such times,

a current is supplied to the filament 13 of the getter bulb 2, a small amount of calcium will be vaporized byheat from the filament l4: and themetal vapor and film deposited without impairment of the device in any manner. I

'In the operation of the getter tube t may be advantageous-under certain conditions to flash the filament 14 either constantly or at substantially regular intervals of time.

Such operation may be desirable owing to the tendency of a calcium surface to become contaminated in absorbing gases and thereb calcium wire which is used in connection with the getter tube is provided with a magnesium eoatmg which will eifectively protect the calcium from oxidation for a considerable period of time, even when directly exposed to the action of the atmosphere.

If desired, the discharge device may, to

, a considerable extent, be evacuated originally by means of the getter bulb alone rather than by means of a pump. Furthermore, discharge devices which have been discarded on account ofvery slow air leaks or because of amount of gassing ma be again operated etficientl when provi ed with a getter bulb of the ty e described. With a getter bulb permanent y attached to a discharge device, 1t is possible to maintain a pressure in the discharge device which is Very much lower than that obtained by the use of a pump, and as a result of the low pressurethus produced,-it is possible, without increasing the size of the anode, to operate a discharge device at voltages which are very much higher than would be possible with a less perfect vacuum.

With a getter bulb of the size indicated,

the pressure in a relatively large power tube,

as for example, a 10 k. w. tube may be maintained at .1 to .0001 microns as long as any active getter material remains in the bulb. Since the amount of gettermaterial flashed ofli' at intervals is very small compared with the in the holder 11, the arrangement disclosed provides a producing and maintainingvacuum in a discharge device thereby prolonging the useful lifeof such a device far beyond the limit reached without the aid of an attached tube 1. If desired the lead-in wire 9 may extend throughathe glass press 16 so that a potential pplied thereto as'well as to the filament 14. In this manner the getter tube may act as a two-element rectifier. Furtherhigh power tube.

3 negative grid current rises current. circuit for getter material originally placed simple, inexpensive and very ef-' fective means of Y -a high degree of small getter bulb,

more, the use of the getter holder as an electrode may allow -measurements of getter metal evaporation to be made if desired.

I have indicated in Figs. 4-and 5 two ways in which the operation of the getter tube 2 may be automatically controlled. It is well known that in a 3-ele1nent tube the degree of vacuum may be determined by measuring the flow of positive ions to a negatively charged electrode such as the grid. When the grid is negative, for example, the grid current which is a so-called positive ionization current is directly proportional to the gas pressure in the tube, other factors being constant. In actual devices this current may vary from 10 to 100 micro-amperes for a good vacuum in a In the arrangement disclosed in Fig. 4, I have taken advantage of the relationship between negative grid curv 3 rent and the vacuum in the discharge device 'loseuts power as a getter. Originally, the

to automatically control the operation of a getter tube associated with the discharge device. In this figure, I have designated the thermionic vacuum device by the reference numeral 2 and the getter bulb by the reference numeral 7. The grid current passes through the resistance element 17. In order, however. to use only the negative grid current a rectifier unit, such as a kenotron 18 is employed. Kenotron 18 and a relay 19 are connected in series with each other and in shunt. with the resistor 17. When the vacuum in the discharge device 2 decreases, the

and operates relav 19. Relay 19 may, of course. be adjusted to operate at any predetermined value of Energization of relay 19 closes a a coil 20 controlling a switch 21 in circuit with a source of energy 22 and the heater filament 14 of the getter tube. The the current supplied to filament 14 vaporizes the calcium in the getter tube and thereby restores the high vacuum in the discharge device 2 whereupon the grid current decreases and relay 19 is deenergized.

If desired the filament 14 of the getter tube may be energized at substantially regular intervals by means of a timing device 23, as indicated in Fig. '5. Although I have illustrated in Figs. 4 and 5 means for automaticallv controlling the heater coil of the getter bulb it will be obvious that in either of these arrangements the circuit of the heater coil may be c osed continuously if desired, so that a relatively small amount of calcium may be vaporized continuously during the operation of. the thermionic device.

Although I have disclosed a relatively it may be found desirable to vary the size of the bulb employed, and

. for a larger power tube as. for example. a .100 k. w. tube I may em loy not onl a larger getter bulb. p y

also a arger amount of getter material.

Wha I claim as new and desire to secure than that indicated but Iii by Letters Patent of the United States, is

l. lln combination, a thermionic vacuum device, a container mounted in said device, said container being provided with a material capable of combining with all common gases, a heating, coil within said device and surrounding said container, and means for energizing said coil at will to vaporize a part of said material and thereby maintain a high degree of vacuum in the thermionic device.

2. ln combination, a thermionic device comprising an evacuated container, said con- CERTIFICATE or CORRECTION,

Watent No. 1,712, 370'.

Granted May 7, 192 9 to v WILLIAM 0. WHITE.

it is hereby certified that error appears in the printcdspecification of the above numbered patent requiring correction as follows: Page 3, line 18, claim 2, heiore the word "capable" insert the words container being provided with a inatei'ialh and that the said- Letters Patent'should be read with thiscorrection therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 11th day of June, A. 1). 1929. a r

(can

, J. Moore, Acting Commissioner of'Patente.

CERTIFICATE OF CORRECTION.

Patent No. 1,712,370. Granted May 7, 1929, to

WTLLTAM G. WHITE.

it is hereby certified that error appears in the printed specification of the above nnrnoere patent requiring correction as follows: Page 3, line 18, claim 2, before the word "capable" insert the words "container being provided with a material"; and that the said Letters Patent should be read with this correction therein that the some may conform to the record ot the case in the Patent Office.

Signed and sealed this 11th day of June, A. D. 1929.

' M, J. Moore,

(Seal) Acting Commissioner of Patents.

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