US2190697A - Electron discharge valve - Google Patents

Description

Feb, 20, 1940.

c. s. BULL 2, ELECTRON DISCHARGE VALVE Filed April 30,- 1938 INVENTOR CABOT SEATON BULL Y ATTORNEY inserted in Patented Feb. 20, 1940 UNITED STAT than? FrlcE ELECTRON DISCHARGE VALVE Cabot .Seaton Bull, Hillingdon,

England, as-

signor to Electric 8; ll/Eusical Industries Limited, Hayes, Middlese company X, England, a British Application April 30, 1938," Serial No. 205,275 In Great Britain May '7, 1937 4 Claims. (or. 250 215 This invention relates to electron discharge valves.

Electron discharge valves as at present constructed suffer from the disadvantage that when a space charge limited current flows noise is present which is due to the fluctuations of current as l pressed by a factor R where REE/g2 9 being the slope of the valve and being the mean square noise current. If, now, two such valves be connected in parallel, with their anodes, grids and cathodes respectively connected, and their anodes connected to a common load, the addition of. the two equal fluctuating currents "i will give a total. noise output of whilst the slope will be 2g. The noise/signal ratio of the combination will then be given by which, from at abovajwill be found to be equal to VZR In other words, the-use of two valves in parallel as described above willv reduce the noise/signal ratio. It has been found by experiment that the use of two valves in this manner does, in fact, serve to reduce the noise/signal ratio. The abo e statements are based on the assumption that the two valves are entirely separate entities. It has, however, been found by experiment that if the equivalent of the two valves are a sale envelope, the equivalent of the two valves merely being afforded by doubling the size of respective components, the improvement in the noise/signal ratio is not obtained. This, it is believed, is due to the fact that the electron err ion from individual portions of the cathode mutually interact thereby increasing the noise. l

It will be appreciated that the use of two or more separate valves in parallel is an inconvenient and costly expedient for the improvement of the noise/signal ratio and if a duplicatenumber of 5 electrodes were inserted in a single envelope such an arrangement would render the construction of the valve cumbersome.

It is the object therefore of the present invention to provide an improved valve of which the noise/signal ratio is improved whilst at the same time avoiding complication of valve construction, the improvement of the present invention being based upon the principle underlying the reduction in noise/signal ratio" which results from the use of two or more valves inparallel.

According to the invention an electron dis charge valve is provided comprising asource of electrons, an anode, and, if desired, one or more additional electrodes wherein the electron emission from said source is arranged to be in the form of a plurality of substantially separate streams and the arrangement is such that when a space charge limited current fiows the individual space charges of the streams are separated to such an extent that they are substantially prevented from mutually interacting, whereby noise is reduced.

Although it is feasible according to the invention to employ two entirely separate cathodes in I a valve and to take steps by shielding or by other suitable means to ensure that the space charges of the electron emission from the individual cathvention will hereinafter be described.

odes are prevented from interacting, it is, however, preferable to employ. a single cathode and to so construct the cathode or to take other steps, as hereinafter referred to, to ensure that a plurality of separate streamsresult, the space charges of which are substantially non-interacting. Several dilierent constructions according to the in- Itisiound that the. improvement in the noise/signal ratio resulting from a valve constructed in accordance with the invention is less at high frequencies than at low frequencies.

In order that the said inventionmay be clearly invention where the separate streams are obtained by the use of partitions.

The valve shown in Figure 1 comprises a directly heated cathode 6, a control grid ill and an anode l l, the electrodes being mounted within an evacuated envelope !2, in known manner. The cathode 9, as shown more clearly in Figure 2, is provided at intervals along its length with fins or other projections 53, the fins or other projections being composed of nickel wire or sheet welded or otherwise attached to the filament at intervals along its length. These fins or projections cause the electron emission from the filament to be confined substantially to predetermined zones, the fins or projections being of such a size that when a space zones are so separated that the space charges are prevented from mutually interacting, that is to say, the separation is such that electrons from one zone are prevented from passing to the space charge of another zone. The desired effect may be obtained by making the fins or other projections of a sufiiciently large area or by making the fins or other projections of such a nature that the filament is cooled over a relatively large portion of its length so as to provide a wide separation between the emission of the predetermined zones. The fins or projections it, since they are connected to the filament, will in operation be maintained at the same potential as that of the filament and this will serve to cause the space charges in the predetermined zones to be shielded and the separation enhanced by an electrostatic eiiect.

Figure 3 of the drawing illustratesa filament similar in form to that shown in Figure 2, the filament of Figure 3 being an activated filament and the emission therefrom is confined to predetermined zones by taking steps to ensure that certain portions of the filament indicated at M are not activated during manufacture or are de activated during or after manufacture. By making the portions [4 of a sutficient size the space charge in the individual streams can be prevented from interacting.

Figure 4 of the drawing shows a conventional form of indirectly heated cathode which comprises an elongated rectangular casing having therein a heating element the exterior of the casing being activated in known manner. The activated area of the cathode is divided into two zones by the provision of an area [5 which is formed by ole-activating the emissive material or by ensuring, during manufacture, that the emissive material is only applied to the casing over certain areas of the casing leaving a nonactivated portion l5.

It will be appreciated that in the above examples and in the examples which follow, the emissive areas of the cathode need not only be divided only into two streams but may be divided, if desired, into more than two streams. Preferably, in all cases the emissive areas of the oathode are of nearly equal area.

Wherethe invention is applied to valves having one or more grids, the provision of the separate emissive streams may be effected, as shown in Figure 5, by providing on the grid 16 nearest the cathode 9 a partition H which projects in close proximity to the cathode. Alternatively, the partition H, as shown in Figure 6, may be mounted on the cathode 9 so as to project into close proximity to the grid l6 which is surrounded by the anode Il, here indicated schematically. The partition I? serves to afilord substantially separate electron emissive streams and, in addition, since the partitions are connected either to the grid 56 or to the cathode 9 and will, therefore, be maintained at substantially the same potentials as the elements to which they are connected, which elements will normally be maintained either at negative or earth potentials, the partitions will serve to provide an electrostatic eiiect to separate the individual space charges and so prevent them from mutually inter-acting.

It is preferable in all cases where the invention is appliedto grid-controlled valves to ensure that the gridwires, or the equivalent of other portions of other forms of grid, are opposite to the emissive areas of the cathode; in other words, the apertures in the grid are not aligned with the emissive portions of the cathode.

The invention may be applied to various forms of valves, such as diodes, triodes and multigrid valves.

I claim:-

1. An electron discharge device comprising an elongated cathode, an equipotential grid surrounding and coextensive with said cathode and having grid conductors opposite the electron emitting surface of said cathode, an anode surrounding and coextensive with said grid, and a conductive member mounted on and connected to said cathode intermediate the ends of said cathode and extending transversely of said cathode a part of the distance only between said cathode and said grid to separate the space charges in space current flow to said anode from emitting portions of said cathode on opposite sides of said member. 1

2. An electron discharge device comprising an elongated cathode, an equipotential grid surrounding and coextensive with said cathode and having grid conductors opposite the electron emitting surface of said cathode, an anode surrounding and coextensive with said grid, said cathode being provided intermediate its ends with a metal projection extending transversely of said cathode into the space between said cathode and said grid a distance less than said cathode-grid spacing.

3. An electron discharge device comprising a rectilinear unipotential cathode electrode, an equipotential grid electrode surrounding and coextensive with said cathode and having grid conductors opposite the electron emitting surface of said cathode, an anode surrounding and coextensive with said grid, and a metal member extending into the space between said cathode electrode and said grid electrode intermediate the ends of said grid a distance less than said cathode-grid spacing, said metal member being mounted on and connected to one of said electrodes.

4. An electron discharge device comprising a rectilinear unipotential cathode, an equipotential grid surrounding and coextensive with said cathode and having grid conductors opposite the electron emitting surface of said cathode, an anode surrounding and coextensive with said grid, and a metallic disc mounted on and electrically connected to said cathode at a point intermediate the ends of said cathode and extending transversely of the longitudinal axis of said cathode and with a diameter slightly less than the inner diameter of said grid.

CABOI' SEATON BULL.

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