US1987711A - Vacuum electric tube device - Google Patents

Description

Jan. 15, 1935. o s 1,987,111

VACUUM ELECTRIC TUB-EV DEVICE Filed Sept. 21, 1928 2 Sheets-Sheet 1 IN VENTOB I [mesf )amonaabinsm.

I ATTOENE Y Jan. 15, 1935. 5.. Y. ROBINSON 1,987,711

VACUUM ELECTRIC TUBE DEVICE Filed Sept. 21, 1928 2Sheets-Sheet 2 N VENTOE Enesf )amanfiob/hson.

AT'TOENEY Patented Jan. 15, 1935 Ernest Yeoman Rob signor to Associa n,- Enfield, England, as

Electrical Industries Limited, a company of Great Britain Application September 21, 1928, Serial No.

In Great Britain September 23, 1927 Claims,

This invention relates to vacuum electric tube devices of the kind having cathodes which are indirectly heated by means of auxiliary members such as resistance heaters, although the auxiliary 5 members may be in the form of electron emitting cathodes and arranged to heat main cathodes at least in part by bombardment.

Vacuum electric tubes'of the kind specified as heretofore proposed have generally been arranged or constructed so that the auxiliary member or heater can be operated from a low voltage supply such as from 4-12 volts in which case the member usually consists of tungsten, carbon or other refractory filaments in comparatively short lengths. r

One such arrangement of indirectly heated cathode has been proposed in which a helix of tungsten or the like, wound to a comparatively small diameter is closelysurrounded by a tube of insulating refractory material the outer surface of which is coated with metal and alkaline earth oxides. 3

In another proposed arrangement a'length of tungsten or like refractory filament is wound helically upon a core or spool of insulating material a coating of alundum cement being subsequently provided in turn surrounded by a closely fitting metal tube constituting the cathode proper which tube may be oxide coated. I With prior arrangements it'has been found that during operation the refractory material becomes conductive when operated at a red heat and due to its contact with the metal cathode frequently breaks down and behaves as a pyro-electric conductor. Furthermore, when direct current is used for the heater undesirable electrolysis occurs resulting frequently in the rapid destruction of the heater filament.

According to the present invention the disadvantages above referred to are avoided or minimized, in the firstplace by separating as far apart as possible the ends of the heater coil and their connecting wires which are in contact with the insulating material, in the second place by spacing the insulating material'from the cathode at all places where the latter operates at incandescence and in the third place, in cases where the heater and cathode are directly registered with respect to one another, by arranging that the necessary mechanical engagementbetweenl the members is located at places which are so cool that conduction and electrolysis will not occur to an undesirable extent.

5 By the invention a vacuum electric tube device may be constructed having a cathode adap ted' to be heated by a resistance heater which can be directly supplied from sources of comparatively high voltage such'as of 50 volts or more and even up to 250 volts and particularly from direct current house mains, whilst the cathode can be constructed with a small sectional perimeter as is desirable in order that the consumption of heating energy may be low, so that grid emission may be absent or negligible and so that hum due to supply ripples may be of no consequence. 10

Another feature of the invention consists in the use in a vacuum electric tube device of the kind specified and suitable more particularly for high voltages, of a carbon filament wound or formed upon the insulating support and preferably prepared by first winding a cellulose, or other thread capable of producing a carbon filament, upon a porcelain or other refractory bobbin or former and heating the latter with the thread thereon in a reducing atmosphere to convert the thread to carbon, thereby to obtain. a formed carbon filament supported on a refractory insulating support. The carbonization may be carried out in any .of the methods known in the carbon lamp filament art. For instance, the 25 support with the thread thereon may be heated to a red heat in powdered charcoal. In order that terminals for such a carbon heater may be provided metal connectors are preferably attached to the ends of the support in engagement with thethread before carbonization is effected. According to a further feature of the invention fuses are inserted in the heater circuit at the two ends of the heater and are located within the evacuated envelope of the device so that in the 35 event of the heater touching the cathode the fuses will blow and disconnect the heater from the supply mains.

In carrying out the invention the insulating support and the cathode tube are extended be- 0 yond their active-portions, that is to say, beyond the electron emitting portion of the cathode and the hotportion of the support and at these extended portions engage one another for the purposes of relative location as is necessary since the heater is required to be close to but separated from the cathode.

In a preferred arrangement which itself and the modifications described constitute features of invention, the heater filament is in the form of 0 a helix of tungsten, molybdenum or carbon upon I the. central portion of a comparatively long slender rod of porcelaimquartz or other suitable refractory insulating material and the cathode comprises-a tube of substantially the same length central portion only, namely along a length roughly corresponding to the length of the heater winding. The insulating rod and the cathode areregistered with respect to one another either by increasing the diameter of the rod at its end so that it engages with the ends only of the oathode tube, or washers of insulating materialor -by the insulating rod directly or through the intermediary of washers. Alternatively the rod may be registered with respectto the cathode tube by means of narrow U-shaped. clips having central perforations for the ends of the rod' and with their arms engaging the ends of the cathode tube. In any of these arrangements the ends of the heater filament may be brought out through the perforations.

To enable the invention to be clearly understood it will now be described with reference to the accompanying drawings which show by way of example several structures in accordance with the invention.

Fig. 1 is a sectional illustration of one electrode structure and Fig. 2 is a plan view thereof.

' Figs. 3, 4, 5 and 6 are elevations on an enlarged scale of the upper. ends of modified forms of indirectly heated cathode. Fig. '7 is a plan view oi the form shown in Fig. '6. Fig. 8 is a sectional elevation of a still further electrode structure, and Fig. 9 a plan View thereof. Figs. 10 and 11 are respectively, an elevation and a plan of the upper end of an electrode structure which is a modification of that shown in Figs. 3 and 9. Fig. 12 is an elevation of a, still further electrode structure,

Referring first to Figs. 1 and 2 oil the drawings, the electrode structure therein illustrated comprises an anode l. secured to a wire 2 carried hi the pinch or seal 3 which may form part of the usual foot of the valve envelope. Within the anode 1 is a helical grid t secured to a support wire 5 which is carried in a tube 8 secured in the pinch or seal The support wires 2 and 5 are tied together at their upper projecting ends by means of a glass bead 2' having'rused in it wires 8 which are in tum welded to said support wires.

located within the grid i is a cathode 9 comprising a metal tube which is coated with electron emitting oxide or oxides preferably only along that part of it which lies within the grid. That is to say, the end portions of said cathode v be wire for-the cathode. At its upper end the oath-- ode is welded to two wires 11 which are fused into the glass head 7. Within the cathode tube 9 is a heater comprising a rod 12 of insulating material consisting preferably of porcelain or quartz on which is a helical winding 13 of tungsten, molybdenum or carbon filament. Said helical winding extends along the rod 12 the length of the main electrodes. That is to say, there is no winding proper at the ends of the rod, W111 6. 25

as the rod, but having the oxide coating in its pass through the perforations of washers 14 which are also preferably of porcelain and which are located within the ends of the cathode tube 9. The washers 14 may be retained within the tube 9 by crimping or otherwise deforming the latter. Conveniently the rod 12 at its lower and engages in a socket 15 which is held in the pinch or seal 3, said socket being connected with a lead-in wire at one end of the heater which is welded to the socket at 16. The other end 17 of theheater winding passes around outside the electrodes to a lead-in wire 18 extending from the pinch or seal 3. Preferably the upper end 17 of the heater winding is welded to a steadying wire 19 secured in the glass head '7. Preferably the rod 12 is otherwise free to slide within the washers 14 but is retained within the socket 15, for instance by pinching the latter.-

With the construction of cathode above described it will be appreciated that the washers 1e are located atplaces where the cathode tube 9 and rod 12 are cool so that no appreciable conduction or electrolysis will occur. No appreciable conduction or electrolysis will occur along the central portion of the rod since there will be a low voltage drop between consecutive turns of the heater winding 13.

Referring now to Fig. 3, in the modified cathode structure therein illustrated therod 12 is located with respect to the cathode tube 9 by means of the washer is which is retained in position within the tube 9 by crimping the latter at 20 and turning over the end at 21. The cathode tube 9 is provided with perforations 22 so as to leave comparatively thin arms 23 which are integral with the central or active portion of the cathode and with the cool and inactive end portion. The end 17 of the heater winding may be led out through one of the perforations 22 of which there are conveniently three.

In Fig. 4 no washers such as 14 are employed, the refractory insulating rod 12 engaging dire ly the inwardly flanged end 24 of the cathode tube 9, which latter is preferably provided with at least one perforation such as 22 through which the end 17 of the heater wire may pass as clearly shown.

In Fig. 5 the end of the cathode tube 9 is expanded, as shown at 25', to receive a comparatively large insulating washer 1411, the latter being retained by turning in the edges of the expanded portion of the cathode tube as imitcated at 26.

In Figs. 6 and '7 the refractory insulating rod 12 andthe cathode tube 9 are registered with respect to one another by means of a U-shaped strip of metal '27 having a central perforation 28 through which the end of the rod 12 passes, the side por tions 29' of the member 27 gripping and preferably being welded to the end of the cathode tube 9.

Referring now to Figs. 8 and 9 oi. the drawings, the'electrode structure therein illustrated com- "prises. as before, an anode 1, grid 4, a cathode tube 9 and a rod 12 carrying the heater winding 13. The anode is carried on two supporting wires 2 and the grid on two supporting wires 5. v

The refractory insulating rod 12 carries at its ends 'nickel clamping rings or bands 30 for the ends of-the helical heater winding 13. The cathode tube 9 is supported at its lower end as before by means of two wires 10 carried in the pinch or seal 3, whilst the rod 12 at its lower end is supported in the socket 15. At its upper end the rod 12 is slidably engaged in an eye 31 carried by or integral with a wire 32 which is fused into the glassbead 7 which is secured by means of'wires 8 to the anode supporting wires 2. The end 1'! of theheater. winding is welded to the wire 32 toiently consists ofmica and which is shown separately in Fig. 11. Said plate 35 is provided-with a plurality of perforations appropriate to the wires which extend beyond the upper ends of the electrodes, the cathode tube 9 in particular having welded to it a pair of upwardly extending wires 36. The mica plate 35 may be held in position by means of a pair of U-shaped wires 37 welded to the upper extensions of the. anode supporting wires 2. An additional hole 38 is provided in the mica plate 35 to locate and accommodate a down lead from the upper end of the heater winding (not shown in Figs. 10 and 11) In Fig. 12 is shown a structure which is modifled to the'exten't that .the cathode tube 9 is located in position by means of discs or washers 39 .which are secured to additional and externally disposed support wires 40 extending upwards from vided with a U-shaped member such as the member 2'7 shown in Figs. 6 and 7. -In addition a limiting stop for each end of .therod 12 is pro- "vided, consisting of an additional member 42 fects to occur thereon rather than on the filament, the rod at least at its ends being preferably made tubular to receive the guard member-which may consist simply of wires extending into the ends of the tube.

In any of the electrode structures illustrated one or both of the leads fromthe end of the helical-heater winding to the corresponding lead-in wires extending from the pinch may comprise or have associated in them a fuse or fuses. Su fuses may comprise short pieces of thin wire of such material and diameter as to be effected for the particularvoltage contemplated. such wires being located between the ends of the heater fllament and its lead wires or members. cases the fuses may comprise in fact integral extensions of the heater wire if the heater wire' is cooled by the insulating material on whichit is wound so that an excess current will causethe fuse portions to blow before the heater itself will blow.

Insome- As previously herein set forth the heater filament 13 may consist of carbon formed in the manner described and connectors such as the metal clamping rings or bands 30 shown in Figs. 8, 10 and 12 'ma'y be employed for such filament.

' It will be understood that various modifications may be made without departing from the scope of the invention. I

I claim as my invention:'' l. The manufacture of a heater for a cathode of the type set forth, which consists in assembling a winding of material having a cellulose base with a refractory insulating support, heating the as-. sembled unit out of contact with oxidizing gases to carbonize the winding, and then assembling the heater and support with the other electrodes.

2. The manufacture of a heater as claimed in claim 1 in which the helix is secured to the support by clamps before the carbonization. I

3. In an electron-discharge.device, a cathode comprising a helically wound type of heater filament supported along its length by a refractory supporting element of insulating materiahsaid refractory element extending beyond the vicinity of said heater filament, electron-emissive means surrounding said heater filament, and means for supporting said refractory element at a point substantially removed from said filament.

4. In an electron-discharge device, a cathode comprising a refractory supporting element of in- 'sulating material, a heater filament helically wound along the middle portion of said supporting element, an electron-emissivetube surrounding said heater filament, and supporting means in contact with the ends of said element for holding it in fixed relation to said tube, said supportingmeans being located at arpoint substantially re-'- moved from said filament.

5. In an electron-discharge device, a cathode ERNEST YEOMAN ROBINSON. I

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