US2613331A - Screen grid structure for electron discharge tubes - Google Patents

Description

Oct. 7, 1952 J. L. H. JONKER ET AL SCREEN GRID STRUCTURE FOR ELECTRON DISCHARGE TUBES Filed July 15, 1946 Patented Oct. 7, 1952 UNITE D. STATES OFFICE.

' s I asiassi Y a 1 I SCREEN Gan) STRUCTURE FOR ELECTRON DISCHARGE 1 Johan" Lodewijk Hendrik Jonker-andAdrianus Johannes Wilhelmus Marie van Overbeek,

- Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford,

Conn as trustee ApplicationJuly 15, 1946; Serial No.'683,59l

In the Netherlands-February16,- 1943' Section 1, Public Law can, August 8, 194

Patent expires February 16', 1963 The presentinvention relates to an electric dis charge tube which comprises at least two control grids and wherein a positive screen electrode 1 Claimr (or. 313-300) is arranged between these grids;and, more particularly, to the construction'of thisscreen electrode. T i

The electron. current is checked by a control grid to a largeror smaller proportion according to the potential of this grid. The checked elec trons may return in this case and may give rise to negative space charges in the neighborhood of the cathode Or of a preceding grid, which may be undesirable.- This phenomenon is particularly inconvenient in the case of tubes with two or more control grids, as in frequency changers, for example, hexodes, heptodes, octodes and the like.

In tubes of this type wherein generally a screen grid is arranged between thetwo control grids, this screen'grid may be wound very tightly in order to intercept the electrons which return from the second control grid. In this case, however, a large proportion of the electron current is directly intercepted by this screen grid, which causes a decrease in the slope of the characteristic curve of the tube.

It is furthermore known to give the second control grid such a shape or position that the returning electrons are deflected in a determined manner and reach one or more suppressor electrodes specially provided for this p p 50 that they cannot return to the neighborhood of the first control grid. This method has the drawback that to direct the said electrons along another path the returning electrons need a certain space, due to which there are produced undesired space charges which impede the passage of a larger electron current, which results in a decrease in the slope of the characteristic curve of the tube. Moreover, in this case the electron current is frequently directed to thesecond control grid at a certain angle in order to impart to the electrons which return a lateral velocity component in the direction of the said suppressor electrodes so that the whole of the electron current is only allowed to pass when the control grid has a positive voltage, which causes inconveniences due to the fact that the grid begins to carry current. This inconvenience is particularly prevalent when use is made of automatic,

volume control.

According to the inven'ion, the above-men tion'ed drawbacks are considerably reduced if inarrelectric discharge tube which is equipped with an electrode system comprising at least two control grids and whereina positive screen electrode is arranged between these grids, the screen -'e1ectr'ode consists of a plurality of plate-shaped 'parts'wh'o'se faces are parallel or substantially parallel to the principal directionof the electron paths," forit has been ioundthat even if the electron current arrives on the face of a control grid at a right angle, rn 'remrmng electrons acquire-acornponent of lateral movement. This is 'caused bythe unequal-potential distribution in the face of this control 'grid'dueto the presence of the grid'wires. 'It is thus possible to intercept the returning electrons with the aid of the screen electrode-according to the invention without any risk of an appreciable proportion ofjthe principal current being taken away'by this screen electrode. Since the returning electrons are required to travel very short distances in order to reach the plate-shaped portions of the screen electrode, the space charges are small so that the slope of the characteristic curve may be increased. Since there is no objection to electrons arriving at right angles to the surface of the particular control grid because the returning electrons acquire a lateral component of velocity in any case, an increased slope can likewise be obtained by permitting electrons to reach the second controlgrid at right angles so that substantially the entire electron current will pass the latter grid at a grid voltage of 0 volt with respect to the cathode.

The plate-shaped parts of the screen electrode may be provided in diiierent ways. Care must be taken, however, to ensure that the narrow sides of these portions are always turned towards the cathode so that as few electrons of the principal current as possible are intercepted. In this case the plate-shaped parts may be constituted by a plurality of flat rings arranged at some distance above one another. It is also possible, however, to build up the screen electrode from a plurality of strips which are arranged according to the direction of the length of the cathode; here again the narrow sides must be turnedtowards the cathode. It is also possible to arrange such strips at an acute angle with respect to the longitudinal Fig. 2 elucidates the eifec't arm; electrode ac cording to the invention.

Fig. 3 is a cross-sectional view of an electric discharge tube embodying an electrode in accord ance with another embodiment of the invention.

Fig. 4 is a cross-sectional view of an electric discharge tube embodying an electrode in accordtube shown in Fig. 3 comprises within an envelope 10 an electrode assembly consisting of a cathode 4, a first grid 5, a second grid 8, an anode 8 and interposed between the grids 5 and 6 a screen electrode la in the form of a plurality of strips arranged parallel to the longitudinal axis of the cathode. In-the-arrangement'oi Fig. '4 the screen electrode shown as lb is in the form of a honeycomb; the remaining parts of the tube being the same as previously described.

What we claim is:

.An' electric discharge tube comprising an en- 'velope, a set of concentric electrodes within said envelopev comprising an anode, a cathode, two

electron permeable control grids interposed between said anode and said cathode, and a screen grid interposed between said control grids and consisting of a plurality of thin substantially planarstrips having spacings therebetween, the

ance with a further embodiment of the invenf tion.

In Fig. 1 the electron paths of the principal current and the paths along which the electrons are repelled by av control grid 3 are denoted by l and 2 respectively. Therepelled electrons generally acquire a lateral speed component due to the presence of thegrid wi'res 3.-

Fig. 2 represents acathode 4 from which the electrons pass through a grid 5 to a control grid 6. According to the invention plate-shaped parts I are arranged parallel to the electron paths l.

After having covered a short distance the electrons repelled according to the paths -2 are intercepted by the screen parts I which may have the shape of flat rings. rings 1 are arranged at a short distance above one another and. are united to form an electrode. W

One form of construction has been described above in. detail. However. it is evident that, as has been mentioned hereinbetore, the that parts of the electrode according to the invention may also be provided in other: ways. Thedischarge longest dimension of each portion being greater than the said spacing between adjacent portions,

said strips being disposed substantially coincident with radial planes through the axis of said cathode.

J OHAN LODEWIJ K HENDRIK JONKER. ADRIANUS JOHANNES WILHELMUS VAN OVERBEE-K.

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS

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