US2582203A - Electric discharge tube - Google Patents

Description

Jan. 8, 1952 J. L. H. JONKER ET AL ELECTRIC DISCHARGE TUBE Filed Dec. 6/1947 J,L,H,JONKER & G. DIEMER INVENTOR$ AGENT Patented Jan. 8, 1952 ELECTRIC DISCHARGE TUBE Johan Lodewiik Hen rik Junker and Gesin s Diemer, Einclh ven, Netherlands, as ign rs to Hartford National Bank, and Trust Company, Hartford, 001.111., s r e Application December 6, 1947, Serial No; 799,054 In the Netherlands November 2, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires November 2, 1966 4 Claims. (Cl. 313-299) This invention relates to devices comprising an electric discharge tube for amplifying or generating electrical oscillations and to tubes for use in such devices.

One of the magnitudes considered with discharge tubes for such a device is the anode current-control grid voltage characteristic curve i. e. the Ia-Vg characteristic curve. As is wellknown, in the case of a triode this curve varies in accordance with the 3/2 power curve, whereas for other tubes it differs more or less from the 3/2 power curve. Consequently, the I'ar-Vg characteristic curve may be considered as substantially rectilinear over a comparatively small portion and hence a small portion only 0! the negative grid-voltage region may be used if a determined permissible distortion percentage must not be exceeded. For the usual working region of the tube this applies to both the static and dynamic Ia-Vg characteristic curves.

Attempts have previously been made to construct amplifying tubes in such manner that distortion occurs to a smaller extent which then becomes manifest in the Ia,-Vg characteristic curve in that this curve is substantially rectilinear over a. greater length. It is known for this purpose to utilise tubes in which the anode current is controlled by deflection of an electron beam. However, such tubes are comparatively complicated and, as a rule, require high voltages for optimum operation.

The said disadvantages may be obviated by the use of a device comprising a discharge tube according to the invention since many experiments have revealed that it is possible to provide for a determined portion of the IaVg characteristic curve and more particularly the portion located in the working region, to be more rectilinear than, the 3/2 power curve. For this purpose applicant has previously suggested that the control and screen grids in a tube should be wound with equal pitch and sopositioned that the active portions, as viewed from the cathode, are located one after another, in which event the ratio between the distance of the grids and the pitch is at least 2:1, whilst the second grid consists of wires the thickness of, which is at least of the pitch. Now, it is possible to obtain substantially the same result by simpler means. For this purpose, in a device for amplifying or generating electrical oscillations, comprising an electric discharge tube having at least a cathode, a control grid and an anode and in which the electron current is concentrated into one or a plurality of beams the width of which varies 2 with the voltage or the control grid, the control grid and the anode are separated by at least one conductive member which is maintained at a fixed positive potential and extends parallel or substantially parallel to the cathode, this member being shaped and positioned in such manner that with control grid voltages in the vicinity of the working point of the tube. this member intercepts the electron current to such extent that the corresponding region of the IaVg characteristic becomes more rectilinear than corresponds to the 3/2 power curve. In case advantage is taken of the fact that, upon variation of the voltage oi the beaming members, in this case for example the supporting rods for the control grid or beaming members connected to this grid, the width of the beam varies. Upon decreasing negative control-grid voltage the width of the beam steadily increases.

The invention takes advantage of this phenomenon for obtaining the effect described.

Owing to the presence of the members according to the invention it may be ensured that upon increasing width of the beam such members are reached, at a certain moment, by the edges of the beam and thus become current-conveying, with the result that the anode current increases to a proportionately smaller extent than in the absence of these members. The members are so shaped and positioned as to be located wholly or for the greater part in the electron current after a determined increase in width of the beam, so that upon further increase of the width of the beamthe current absorbed by these members remains substantially constant. It is thus ensured that in the working region of the tube the slope of the Ic -V9 characteristic curve increases to a smaller extent than corresponds to the 2/3 power curve and hence is more rectilinear.

In the presence of a screen grid such members may either be connected to the grid or integral therewith.

In order to ensure proper operation, the members according to the invention must not be of undue width. As a rule, such members may have a width of 0.3 mm. The construction according to the invention affords the advantage that it may readily be used with existing types of discharge tubes, no other requirements having to be imposed upon the construction and the spacing of the electrodes than those which are already observed in general for satisfactory operation of the tube. Beaming of the electrons is in most cases already ensured to a suflicient extent by the presence of the supporting rods for the control grid if such supporting rods are of sufiicient thickness and provided on each side of the cathode. In this respect also most of the existing tube constructions need not undergo any modification. I

The beaming may be improved, however, by forming the cathode in known manner in an oval, elliptic or circular shape. The lensshaped cross-section of the cathode usually employed for output amplifying tubes, in which the lateral faces are not provided with electronemitting material, is less suitable in this respect. When use is made of such a cathode the beaming eiiect may be improved by providing the control grid in known manner with rods.

The conductive members according to the invention may have the shape of straight rods. The position of such rods may be slightly inclined with respect to the cathode. It as also possible to substitute the rods by strips or plates, in which event they may be, for example, trapezoidal in shape or may acquire an irregular width by providing notches or similar recesses at the edges. in increase of the current intercepted by the said members. For this purpose use could alternatively be made of bent rods. Furthermore it is possible to ensure that the said members serve also as supporting rods for a screen grid. It is possible to utilize a single member but in general a plurality of members will be provided ata distance on each side of a beam which is greater than the minimum width of the beam but smaller than the maximum Width of the beam.

In order that the invention may be clearly understood and readily carried into effect, it will now be described more fully by reference to the accompanying drawing, wherein Fig. 1 and 2 show characteristic curves and Fig. 3 is a cross-sectional view of a determined form of pentode tube according to the invention.

In Fig. 1, reference numeral I indicates a dynamic Ia-Vg characteristic curve of a pentode which varies up to point 13 approximately in accordance with the 3/2 power, whereas reference numeral 2 indicates a characteristic improved in accordance with the invention. The point e is the static working point of the tube. In the case of line 2 the portion ab, which corresponds to the working range of the tube for alternating grid voltages of not undue value, is more rectilinear than the corresponding portion of line I. As can be seen from Fig. 2, this is ensured owing to the fact thatin this region the screen grid starts to convey a proportionately greater current as indicated by line 4 since on account of the voltage variation of the control grid, the width of the electron beams increases to such extent that the thin rods 9, shown in Fig 3, which, in this case, extend parallel to the cathode, become current-conveying. The spacing of these rods is such that approximately half of their width is located within the beam at the working point It is thus possible to control the speed of the tube. This position may be ascertained in asimple manner by way of tests, for example in combinationwith investigations with the rubber sheet. When the rods 9 are located wholly withinthe beam, the increase in screen g id cur-.

rent takes place again in accordance with the initial line 3 (Fig. 2). In Fig. 3 the cathode is indicated by 5, the control grid by S, the screen grid by I and the anode by 8. The screen grid 7 and the anode 8 may be separated by a suppressor grid, not shown, which may be connected to the cathode. The supporting rods 52 for the control grid bring about beaming of the electron current. The beams have a width I with a stron ly negative control-grid voltage. When the beams acquire a width II, the screen-grid current increases to a proportionately greater extent than according to line III. Consequently, this moment must be reached at a negative control-grid voltage corresponding to point a, whilst the rods 9 must preferably be located wholly within the beams at a control-grid voltage corresponding to point b. Upon further decrease in negative control-grid voltage the beams acquire a width as indicated by III in Fig. 3. lhe rods 9 generally require to be of a thickness smaller than that of the supporting rods H, but this thickness may vary in accordance with the length of the region ab and the extent of the variation in width of the beams upon variation of the control-grid voltage. If necessary, the rods may serve assupporting rods for the screen grid, in which event the supporting rods 1 i could be dis pensed with.

What we claim is:

1. An' electric discharge tube comprising a cathode having a given dimension in a given di rection which is smaller than all other dimensions of said cathode, an anode enclosing the cathode, a control grid between the cathode and anode, rods supporting said grid, said rods having a given dimension in a direction parallel to said given direction of the smallest dimension of the cathode which dimension of the rod is of the same order of magnitude as the smallest dimension of the cathode, and an electrode member adapted to have a positive potential applied thereto positioned substantially parallel to said cathode between said control grid and said anode, said rods constituting beam-forming electrodes in the operation of the tube.

2. An electric discharge tube as claimed in claim 1 in which the cathode has an elliptical shape.

3. An electric discharge tube as claimed in claim 1 in which the cathode has a circular shape.

4. An electric discharge tube as claimed in claim 1 in which the rods supporting the control grid are slightly inclined with respect to the cathode.

J OHAN LODEWIJK HENDRIX J ONKER. GESINUS DIEMER.

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

UNITED STATES PATENTS Rothe et a1. Aug. 12, 1941

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