US2841743A - Electron tube device - Google Patents

Description

July i, 1958 H. B. HAARD ELECTRON TUBE DEVICE 2 Sheets-Sheet 1 Filed July 15, 1954 J/Vg NTQR f/mw 352274 HHHRO f i a I H flrromvzr y 1958 H. B. HAARD 2,841,743

v ELECTRON TUBE DEVICE "Filed July 15. 1954 2 Sheets-Sheet 2 ELECTRON TUBE DEVICE Hans Berti wHadrd, Hagersten, Sweden, assignor to Telefonalrtieholaget 'L M Ericsson, Stockholm, Sweden, a corporation of Sweden Application July 15, 1954,5erial No. 443,643

Claims priority, applicationsweden Early 31, 1953 6 Claims. (or. sis-2r This invention relates to an electron tube device provided with a trochotron tube. This .kind of tube is defined for example in U. S. vPatents 2,563,807 and 2,591,997 or in the Transactions of the Royal Institute of Technology, Stockholm, Sweden, Nr. 22, 1948: Theory and application of .trochotrons. A =trochotron tube may be provided with a number of compartments arranged side by side :along a straight line. .By means of control electrodes the electron beam may be directed into any of said compartments. Each compartment is bounded by two adjacent control electrodes at the sides and by a receiving electrode at the bottom. An electronsource is located at one end of the row formed by the compartments, and at the other end there is an idle electrode for catching the electron beam when it is not directed into any of the compartments. The idle electrode is usually extended towards the electron source, and this extended part, which .is usually .called the rail, is arranged parallel to the .row of compartments and faces the same. The compartments are open towards the rail. A trochotron tube of the described type may be provided with further electrodes arranged within the di'fierent compartments, said electrodes being auxiliary electrodes to facilitate direction of the electron beam into the respective compartment.

The trochotron tubes have proved advantageous in pulse multiplex systems as a stepping operation .of the electron beam over the .diiferent receiving electrodes can be readilyprovided 'for combining or distributing the different channel pulses. It .has been proposed to modulate the voltage applied to the control electrodes by the low frequency modulating voltage of the respective channel, whereby the current distribution between the control electrode and the respective receiving electrode may-be varied intime in respect to the modulation. Thus amplitude modulated pulses are obtained across the load impedance of the receiving or the control electrode without special amplitude modulators. This method of modulating the channel pulses has however several serious drawbacks. Owing to the low frequency modulating voltage being permanently applied to all the control electrodes, serious changes in'the field configurationwill appear as a function'of the modulating voltagesof alluchannels, causing crosstalk between the channels. Furthermore, the control electrodes will draw a considerablerpower from the modulating source, sothat additional amplifiers may be necessary in eachchannel.

These disadvantages may be avoided with theelectron tube device according to the present invention. The invention is characterized by each compartment of the trochotron tube comprising in addition to the receiving electrodes, the control electrodes and possibly the auxiliary electrodes, a further electrode, an auxiliary control electrode, which is located between the receiving electrode and a control electrode which serves to direct the current into said compartment. The invention is further characterized by means for feeding said further electrode with a potential, which is negative in relation 184L743 i atented July 1, 1958 2 to the cathode of the tube, and by means for varying said negative potential.

In one embodiment of the invention, applicable to amplitude modulated pulse multiplex system, for generating the amplitude modulated pulse series for the different channels of a pulse multiplex system, the cathode current of the trochotron is pulsed at equal intervals, whereby current pulses are sequentially received in the different compartments. The modulating voltages of the diflerent channels is impressed upon the auxiliary electrode of the compartment associated with the channel, so that amplitude modulatedcurrent pulses are obtained in the respective circuits of receiving electrodes and the control electrodes or the auxiliary electrodes.

By means of this additional auxiliary control electrode the current distribution between the receiving electrode and the control electrode or the auxiliary electrode may be varied without influencing the electric field outside the compartment. Thus crosstalk will be reduced to a negligible value. As the auxiliary control electrode is made negative, the power drain from the modulating source is negligible too and no additional amplification is necessary in the low frequency channel. A voltage step-up transformer is sufficient in most cases.

The .invention will be more closely described in the following with reference to the accompanying drawingsf Fig. 1 illustrates a trochotron having the general shape shown in the above mentioned transactions and is 'pro vided with auxiliary control electrodes according to the invention, Fig. 2 shows two compartments of a tube according to Fig. 1 but with a further auxiliary electrode per compartment, and Fig. 3 shows a circuit comprising a rotational symmetric tube according to the U. S. Patent No. 2,591,997.

The electron tube of the circuit shown in Fig. .1 comprises in an envelope 43 ten receiving SlEClIOCl6'S1'1@, ten control electrodes 114d ten auxiliary control electrodes 214,42, a cathode or source of electrons ill, such as a grid surrounding the cathode, an acceleration anode 44 and an'idle electrode or rail 42. Thus each compartment includes a receiving electrode, for example 5, a control electrode, for example 15, directing the electron beam from the source of electrons to the corresponding .compartrnent, and an auxiliary control electrode, for example 25, located on the same side of the compartment as the control electrode. Said auxiliary control :-electrode .is

- connected to a negative voltage source, for example '72,

77. By varying the negative potential of the auxiliary control electrode, for example'by means of applying a modulation voltage to the electrode through a transformer, "for example 62, 69, the current distributionhctwecnthe plate for example 5, and the following :con trol electrode, for example 14 may be varied. If the potential of the auxiliary control electrode, for example 25, is decreased, an increasing part of the beam will-be directed :to the following control electrode 14, and the currentto that electrode will thus increase. On the other hand, -i-f'the potential of the auxiliary control electrode is increased, the current to the control electrode .M-is reduceclwhile the current to the plate 5 is increased to a corresponding degree.

The receiving electrodes :of the trochotron; shown .in Fig. l are in a usual manner connected to a positive voltage source 43 through a common resistor 46. The control electrodes ll20 are connected to another posi tive voltage source 50 through individual resistors 81-95 The cathode 40 and the rail 42 are grounded at 47 while the grid 41 is connected to a bias source 49, which may be pulsed at the stepping rate. The electron beam is designated by 45.

The device operates in the following manner: By means of any known method the potential of the control electrodes of the tube is sequentially lowered. The electron beam of the trochotron is normally cut off by means of a high negative bias on the control grid 41. The grid 41 is fed with short positive pulses synchronized with the potential decrease of the control electrodes, whereby cathode current is caused to flow to one compartment after the other in short pulses. When the electron beam enters a compartment the electron current is distributed between the receiving electrode and the following control electrode, the distribution depending on the potential of the auxiliary control electrode. Thus the amplitude of the current pulse to a receiving electrode will be proportional to the instantaneous value of the modulating voltage on the auxiliary control electrode. The complex pulse series composed of the diiferent channel pulse series can be taken out across the resistance 46.

With suitable dimensions of the different electrodes of each compartment and with suitableelectrode potentials it is possible to obtain a good control of the current distribution between the receiving electrode and the control electrode of each compartment. However, the current to the control electrode must not increase too much, as then the voltage of the control electrode will fall below the stepping voltage, thereby causing the electron beam to step to the next compartment. In order to obtain an almost 100% modulation withoutthis risk of false stepping an embodiment according to Fig. 2 may be used. This figure shows a detail of two compartments ina tube having the same general shape as the tube shown in Fig. 1. In the tube accordingto Fig. 2 there is provided an additional auxiliary electrode, for example 35, 36, in each compartment. These electrodes are connected to a positive voltage source through individual resistors, for example 55, 56. In thisembodiment the electron current is entirely distributed between the receiving electrode, for example 6, and the following auxiliary electrode, for example 36. The auxiliary electrodes have no influence on the stepping of the electron beam from one compartment to the other.

The invention is not limited to trochotron tubes having the different compartments located in a straight line as shown in Fig. 1 but may as well be applied to a tube having the compartments symmetrically located around a central cathode as is shown for example in the U. S. Patent 2,591,997. A circuit equivalent to the circuit of Fig. 1 but with such symmetrical tube is shown in Fig. 3.

In Fig. 3, 91 is the tube envelope, 92 is the 'cylindric cathode connected to ground and located centrally in relation to the other electrodes of the tube. A control grid 93 encompasses the cathode for controlling the emitted cathode current and is connected to the same terminal 49 as is shown in Fig. 1. Around the cathode the control electrodes 101-110, the auxiliary control electrodes 111120 and the receiving electrodes 121-130 are located in a manner analogous to that shown in Fig. 1. In the tube shown in Fig. 3 the electron beam has the same distance to travel to all receiving electrodes, which is a great advantage owing to the symmetry obtained. In the same manner as is shown in Fig. "1 all the receiving electrodes are connected to the terminal 48 through a common resistance 46, while each control electrode is connected to the terminal 50 through a separate resistance 8190 and each auxiliary control electrode is connected both to a negative terminal, for example. 72, 77, and to a source of modulating voltage, for example 62, 69. The

function of the circuit according to Fig. 3 is the same as shown in conjunction with Fig. 1.

I claim:

. 1. An electron discharge apparatus including a trocho-. tron having several compartments each limited by a receiving electrode, a control electrode and the control electrode of the next following compartment and further having a cathode and means for stepping the electron beam produced by the cathode from compartment to compartment, in combination with an auxiliary control electrode means for each compartment, each of said auxiliary electrode means being disposed between the receiving electrode andthe control electrode of the respective compartment closer to the control electrode of its own compartment than to the control electrode of the next following compartment, a source of a bias potential negative relative to the cathode, connected to each auxiliary control electrode means to render the electrode means active during the discharge, and circuit means for varyingsaid bias potential to vary the distribution of the cathode current between the respective receiving electrode and the respective control electrode.

2. An electrondischarge apparatus according to claim 1, wherein said circuit means for varying the negative bias potential comprise circuit means for applying a modulation voltage to the respective auxiliary control electrode means.

3. An electron discharge apparatus according to claim 2, wherein said circuit means for applying the modulation voltage comprise a number of transformer means each one included in the connection between the respective auxiliary control electrode means and said source of negative bias potential.

4. An electron discharge apparatus according to claim 1, wherein each of said auxiliary control electrode means comprises two auxiliary electrodes, one connected to said source of negative bias potential and the other to a source of positive potential to renderboth electrodes active during the discharge, whereby the electron current is distributed between the respective receiving electrode and the respective one of said other auxiliary electrodes.

5. An electron discharge apparatus according to claim 4, wherein a resistance means is included in the connection between each one of said other auxiliary electrodes and said source of. positive voltage.

6. An electron discharge apparatus according to claim 1 for generating amplitude modulated pulse series in the References Cited in the file of this patent UNITED STATES PATENTS 2,242,289 Snyder, Jr. et a1 July 22, 1947. 2,513,260 Alfven et a1. June 27, 1950 2,591,997 Backmark Apr. 8, 1952 2,620,454 Skellett Dec, 2, 1952 2,706,248 Lindberg et al. Apr. 12, 1955 2,721,955

Fan et al. Oct. 25, 1955

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