US2755411A - Device of the kind comprising an energy amplifying tube having a pentode characteristic curve - Google Patents

Description

y 7, 1956 2. VAN GELDER 2,755,411

DEVICE OF THE. KIND COMPRISING AN ENERGY AMPLIFYING TUBE HAVING A PENTODE CHARACTERISTIC CURVE Filed Dec. 17, 1952 I I I I K 2 I S I j i -q 50- III 1 VOLTS ANODE Fig.l

INVENTOR ZEGER VAN GELDER AGENT United States Patent DEVICE OF THE KIND COMPRISING AN ENERGY AMPLIFYING TUBE HAVING -A PENTODE CHARACTERISTIC CURVE Zeger Van Gelder, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford,

Conn., as trustee Application December 17, 1952, Serial No. 326,445 Claims priority, application Netherlands February 2, 1952 5 Claims. (Cl. 315-13) contrary, is high and drops comparatively strongly at an increase in Va and assumes a definite, comparatively low, substantially constant value at the knee. voltage. Since such tubes usually operate at anode voltages exceeding the knee voltage, the screen grid of such tubes is proportioned to be such that at this comparatively low screen-grid current noexcessive heating of the screen grid occurs. However, in energy amplifying tubes the heating brought about by the screen-grid current is yet so great that, as a rule, particular measures .must be taken to cool the screen grid. For this purpose the screengrid wires have been arranged behind thecontrol-grid wires and cooling members have been provided at the screen-grid stay wires. However, these means are insufficient in those cases. in which the anode voltage is often lower than the knee voltage, so that excessive heating of the screen-grid may occur. This is the case, for example, in definite transmitting tubes and television tubes.

In this case the provision of larger cooling members does not remedy the evil, since the comparatively thin screen-grid wires themselves cannot transmit the heat sufliciently rapidly to the stay rods or the cooling members. These wires must be thin, in' order to intercept a minimum of primary electrons.

' Extensive experiments have nowshown that the said difliculty can be substantially completely avoided, if, in accordance with the invention, in a device comprising an energy amplifying tube having a pentode characteristic curve, in which the electrons emanating from the cathode are concentrated in one or more beams, a number of screens with positive potential are arranged outside the forward electron flow in close proximity to the screen grid. It has been found that these screens are capable of attracting and intercepting the primary electrons which are reflected owing to the spatial charge between the screen grid and the anode.

The electrons reflected by a spatial charge occurring in front of the anode produce a strong increase in screengrid current at low anode voltages. By using a tube according to the invention excessive heating of the screengrid wires can be avoided even at low anode voltages. It was a surprise to find that the reflected electrons, which are otherwise intercepted by the positive screen-grid wires are sufliciently attracted by the positive screens according to the invention to find their way to these screens.

The difficulty caused by reflected electrons also occurs in mixing tubes and electronically coupled mixing tubes 2,755,411 Patented July 17, 1956 and oscillator tubes, inter alia in hexodes, octodes and the like. However, with energy amplifying tubes the conditions are quite different from those occurring in such mixing tubes in which the electrons reflected electrostatically by a control-electrode are reflected in a definite direction. In such tubes the construction of the grids is therefore such that the reflected electrons are directed to screens provided for this purpose. Since such tubes operate with a low electron current, it may be ensured that the electrostatically determined electron paths are affected very little by spatial charge. This is, however, quite different in energy amplifying tubes in which the reflection of electrons occurs more or less irregularly, if high spatial charges occur locally at definite instants. I

In order that the invention may be readily carried into effect, it will now be described in detail with reference to the accompanying drawing, in which Fig. 1 shows a graph of apentode;

Figs. 2 and 3 show tube constructions according to the invention;

Fig. 4 shows the tube illustrated in Fig. 3 in a typical operating circuit.

.Referring now to Fig. 1, reference numeral I designates the IaVa characteristic curve of a tube having pentode characteristics, and II designates the I a-Va characteristic curve of the screen grid of such a tube. At an anode voltage of less than 25 to 50 v., the screen-grid current increases very strongly, so that the known tubes are practically unserviceable at such anode voltages, since the screen-grid is then overloaded. This may be avoided, if for example use is made of an energy amplifying tube of a construction according to the invention, as is shown in Figs. 2. and 3. Fig. 2 shows a spatial-charge tetrode, in which 1 designates the cathode, 2 the control-grid, 3 the screen grid, 4 the anodes and 10 the bulb of the tube. The screens 5, which may, if desired, be replaced by a collecting grid, may be connected to thecathode 1, or be connected outside the tube to zero' potential or to low potential. They may produce at7 a spatial charge, if the anode voltage has a low value, so that the secondary electrons 8 from the anode are withheld and the pentode .characteristic curve shown in Fig. l is produced. It is found that the electrons 9, reflected by the spatial charge, may be attracted by the screens 6, which are kept on a comparatively high positive potential and which may, if necessary, be connected in'the tube to the screen grid 3 in a manner such that these electrons find their way to these screens instead of to the positive screen-grid wires. evident from curve III of Fig. 1, which indicates the variation of the current of these screens 6. Moreover, it is thus avoided that the reflected electrons should pass several times through the system and might produceBarkhausen- Kurz oscillations. The current of the screen grid itself appears to have a variation in accordance with curve 'IV of. Fig. 1. It is evident that at a low Va this exceeds only little that at a high Va. Thus also in the range of low Va excessive heating of the screen-grid wires may be avoided.

It is necessary that the flow of electrons should be concentrated in beams, since otherwise the reflected electrons should traverse in any direction the forward flow of electrons, so that no measures could be taken to intercept only these reflected electrons, since the arrangement of positive screens outside the forward flow of electrons would then not be possible and these screens would then intercept also a great portion of the forward going electrons.

In general, the provision of a control-grid with stay rods suffices to form the beams. This is, for example, the case with a tube as shown in Fig. 3, in which the invention has been carried out in a pentode energy-amplifying tube, comprising a collecting grid. In this figure reference numeral 11 designates the cathode, 12 the control-grid, 13 the screen-grid, 14 the suppressor grid or collecting grid, 15 the w in This is anode and 17 the bulb of the tube. In the proximity of the stayrcdsof the screen grid 13 are provided the screens 16 according to the invention. In certain cases these screens themselves may beshaped as stay members, over which'the screen-grid wires are wound. However, as a mile, it is preferred to arran e and to shape these screens so that they are located not only outside the forwardgoing bearn's, but also for the major part outside the plane of the screen-grid Wires, so that the sucking effect on the electrons, wandering back comparatively slowly, is improved and a minimum quantity of these electrons will find their way to the screen-grid wires themselves. This is particularly of importance, if comparatively wide beams are used, as is the case shown in Fig. 3. The screens may be connected internally to the screen grid. typical ciredit for the tube of Fig. 3 is illustrated in Fig. 4, which shewsthe suppressor grid 14 connected to the cathode 11, and the screens 16 connected internally to the screen grid 13, both therefore being at a relatively high potential relative to the cathode 11.

The eifect of the invention is consequently obtainable only if the flow of electrons is divided into limited beams and it the current density in the beams is so high thatelectrons can be reflected by a high spatial charge. Consequently, the invention is of importance, in general, only for power amplifying tubes, i. e. tubes adapted to operate with a comparatively high electron current, for example, with a mean anode current of more than 25 ma. A The invention is furthermore of importance for all those cases in which electrons reflected by spatial charges give rise to excessive heating of preceding positive grids of thin wires.

Apart from the embodiment shown, other embodiments of the invention are possible. For example, the screens according to the invention may be provided with a sep- 'arate current supply conductor and be quite free from screen grid, but they may, as an alternative, be connected directly to the screen grid. In this case a tube according to the invention comprises two sets of plate-shaped electrodes arranged between the screen grid and the anode, these electrodes being arranged clearly outside the path of the forward flow of electrons, the set nearest the screen grid being connected to this screen grid, the other set to the cathode.

What I claim is:

1. A beam power discharge device having a pentode anode voltage-anode current characteristic for operation with high anode currents, comprising a cathode, control grid, screen grid, suppressor electrode and anode disposed in that order within an envelope, said electrodes being arranged to confine the electron flow between the cathode and anode in a limited area, means for applying a comparatively high positive potential relative to the cathode to thescreen grid and not more than a low positive potential relative to the cathode to the suppressor electrode to thereby produce a high space charge region in the path of the electron fi'ow between the anode and screen grid 4. whereby the tube exhibits a pentode characteristic, a plurality of screens disposed in close proximity to and outside of the screen grid and outside the path of the electron flow, and means connecting said screens to said screen grid to attract primary electrons reflected by the space charge region and thus prevent them from striking the screen grid.

2. A beam power discharge device as claimed in claim 1 in which the screens comprise a pair of bent oppositelydisposed plate-shaped electrodes disposed between the screen grid and the suppressor electrode, each of said electrodes partially embracing a portion of said screen grid.

3. A beam power discharge device as claimed in claim 1 in which the suppressor electrode comprises a first pair of oppositely-disposed bent plate-shaped electrodes located outside the path of electron flow, the screens comprise a second pair of oppositely-disposed bent plate-shaped electrodes disposed coaxially within said first pair and outside the path of electron flow and partially embracing the screen grid, and means are provided connecting the suppressor electrode to the cathode.

4. A circuit including a beam power discharge tube having a pentode anode voltage-anode current characteristic for operation with high anode currents, said tube comprising a cathode, control grid, screen grid, suppressor electrode and anode disposed in that order within an envelope, said electrodes being arranged to confine the electron fiow between the cathode and anode to a limited area, a plurality of screens disposed in close proximity to and outside of said screen grid and outside the path of the electron flow between the cathode and anode, means for maintaining, the screen grid at a comparatively high positive potential relative to the cathode, means for maintaining a potential between zero and a low positive potential relative to the cathode on the suppressor electrode to thereby produce a high space charge region in the path of the electron flow between the anode and screen grid whereby the tube exhibits a pentode characteristic, and means for maintaining said screens at a comparatively high positive potential relative to the cathode and of the order of that maintained on the screen grid to attract primary electrons reflected by the space charge region and thus prevent them from striking the screen grid.

5. A circuit as claimed in claim 4 wherein the screens comprise a pair of bent oppositely-disposed plate-shaped electrodes disposed between the screen grid and the suppressor electrode, each of said electrodes partially embracing a portion of said screen grid.

References Cited in the file of this patent UNITED STATES PATENTS 2,113,801 Shoenberg et a1 Apr. 12, 1938 2,219,102 Herold Oct. 22, 1940 2,228,978' Schade Jan. 14, 1941 2,460,382 Fulton Feb. 1, 1949

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