US1973075A - Space discharge tube - Google Patents

Description

isept. 11, 1934. A. HUND 1,973,075

SPACE DISCHARGE TUBE Filed Feb. 3, 1932 2 Sheets-Sheet l ION/Z/NG c/Pcu/T- INVENTOR August Hmul Patented Sept. 11, 1934 UNITED STATES PATENT OFFICE SPACE DISCHARGE TUBE August Hund, West Orange, N. J., assignor to Wired Radio; Inc., New York, N. Y., a corporationof Delaware Application February 3, 1932, Serial No. 590,561

4 Claims. (Cl. 250-27) electrodes while other electrodes are utilized for generation, modulation, demodulation or amplification of variable currents.

An object of my invention is to provide an electrical discharge tube of this character comprising a plurality of electrodes surrounded by a gas at an attenuated pressure,.two of which electrodes may be characterized as ionization electrodes while preferably a plurality of other electrodes is included in a work circuit the voltage of which may be adjusted independently of the ionizing voltage.

Another object of my invention is to provide a tube of the class described which functions so as to segregate usefully an excess of negatively charged ions in certain localities within the tube, or an excess of positively charged ions, as the case may be.

'Another object of my invention is to provide a tube of the class described in which the electrodes are of suitable formation and so arranged with respect to one another that a high amplification factor in the work circuit may be obtained.

Another object of my invention is to provide a gaseous discharge tube in which an excess of negative ions projected toward one of the electrodes may be so controlled as to producea highly efficient amplification ratio as between the input and output circuits in which said tube is placed.

These and other objects are attained by a novel construction of the electrical discharge tube as will be more fully understood from the following description and by reference to the accompanying drawings, in which:

Fig. 1 depicts one form of an electrical discharge tube having two electrodes in an ionizing circuit and two other electrodes in a work cir cuit;

Fig. 2 is a modification of the tubes of my invention showing electrodes of a suitable formation connected to input and output circuits, respectively;

Fig. 3 is another modification of my invention having five electrodes;

Fig. 4 is a diagram illustrative of certain features of my invention;

Fig. 5 is a characteristic chart showing the actual performance of the tube of Fig. 1; and

Fig. 6 is a simplified circuit diagram applicable to the tube of Fig. 1 and explanatory of-the curves of Fig. 5.

In my copending application, Serial No. 573,076, filed November 5, 1931, an electrical amplifier is shown employing two-element space discharge tubes which exhibit a negative resistance characteristic. In my copending application, Serial No. 579,872 filed December 9, 1931 electrical discharge tubes having three electrodes are shown. Since it is necessary in a two-element or a three-element tube to introduce a protective resistance in the circuit which includes the ionizing electrodes it is not always feasible to operate the tubes under the most satisfactory conditions to exhibit a power gain between the input and output circuits. The voltages applied across the ionization electrodes of such tubes are usually higher than are desirable for work circuits. Furthermore, the useful range of voltage variation in the work circuits of the tubes heretofore known is limited by the fact that if either or both of the ionizing electrodes are also used as work electrodes, that is, in the work circuit, then the latter cannot conveniently be operated below a critical voltage at which a glow discharge is set up. It so happens, however, that the most desirable part of the curve characteristic of the tube is near this critical voltage and relaxation oscillations are apt to occur. Hence the utility of the tube is for the time being destroyed.

For the above reasons tubes made with separate electrodes for the ionizing circuit and for the work circuit respectively have been found to offer considerable advantages over the two-element and three-element tubes. Among these advantages may be mentioned: (1) the fact that the voltage across the work electrodes can be low and that the protective resistance which is essential to the ionizing circuit may be dispensed with in the work circuit; (2) the work circuit may be made operative practically down to a zero voltage; and (3) the ionizing voltage can be maintained well above the critical voltage at which relaxation oscillations will occur, thus avoiding the latter.

The fundamental idea of the present invention is exhibited in Fig. 4 in which any two electrodes, say 31 and 32, may be caused to act as ionization electrodes across which a suitable voltage from the source 9 is impressed through the protective resistance 10. Then, independently of the voltage of the source 9 a different and preferably much lower voltage may be impressed across the electrodes 33 and 34 of the work circuit from the source 26. The voltage drop across the elecused with pressures of one millimeter up to several centimeters.

The tubes when suitably constructed may be used in circuits where it is desirable to exhibit a negative resistance characteristic. In other cases they may be used to bring out a high ratio of amplification by placing the two work-electrodes in a region where there is an excess either of negative ions or of positive ions.

It has been known in the art that gaseous discharge tubes could be used in a limited way for controlling the effects of voltage changes in a work circuit. Attempts, however, to combine the work circuit with the ionizing circuit have been fraught with difllculties due to the facts as set forth above with regard to the critical ionizing potential and with regard to the tendency to set up relaxation oscillations when it is attempted to apply the preferred voltage to the work circuit. The lack of continuity in the glow discharge would, of course, render the tube useless in a radio receiving set. V

Other experimenters, such as Dr. Georg Seibt and Dr. Hellmuth Bley, of Germany, have shown that with a discharge'tube having four electrodes and with peculiarities of construction, such as would exhibit a so-called edge-effect" in the dissipation of electrons, an appreciable amplification could be observed. In contradistinction thereto; the present invention provides a greatly improved system of amplification by arranging the electrodes so as to utilize their entire exposed areas for controlling and translating the input and output currents. It will be seen, therefore, that a number of important advantages are to be derived from the arrangement of electrodes in an electrical discharge tube according to the present invention. The electrodes of the work circuit may be energized with much lower voltages than are required for the glow discharge. In fact, a wide range of voltages is available and the protective resistance which is essential in the ionizing circuit may be removed from the work circuit in which a low impedance path for high frequency currents is sought.

The electrical discharge tubes of my invention are also advantageous from the standpoint of their adaptability to a wide variety of uses and of the flexibility of the circuit arrangements in which the tubes are to be operated. For example, it. is possible to adjust the protective resistance in the ionizing circuit to such a value that no relaxation oscillations will occur, and at the same time to adjust the voltages across the electrodes of the work circuit independently of the ionizing circuit. e

As will be seen from the description to follow, the tubes of my invention can be used for segregating negatively charged ions and electrons in certain places within the tube so that a control similar to that in a thermionic tube is possible.

In some of the tubes constructed according to my invention the electrodes are so arranged that the electrons have a tendency to flyofl beyond the region of maximum ionization, due, possibly. to their smaller mass and to their ability to be projected through space with fewer atomic collisions than attend the projection of positively charged ions. In other words, the mean free path of an electron is much longer than that of a molecule. a This phenomenon I make use'of by positioning the work electrodes where they will -most influentially cooperate in effecting the segregation of the negatively charged ions and electrons. It is not essential, however, that the ions and electrons so segregated should be negatively charged. Under certain conditions an excess of positively charged ions may be caused to 'co-,. operate with the work-electrodes.

The exposed area of the ionizing anode relative to that of the ionizing cathode can be adapted to favor the segregation of ions and electrons of like charge. For example, if the ionization cathode is relatively larger, then it will naturally attract to itself an excess of positively charged ions but the negatively charged ions that are repelled therefrom may have difficulty in reaching the smaller ionization anode. These negatively charged ions and electrons may, however, overshoot the anode and be attracted to one of the otherelectrodes in the tube while their effects are being controlled by the potential applied to the control electrode.

Referring now to Fig. 1, a discharge tube is shown the outer structure of which is of the wellknowntype having a base 1, an envelope 2, and

prongs 3. The ionization cathode 4 and ionization anode 5 are placed in an ionization circuit and may be in the form of rings of round or flat wire or some other suitable shape. Each of these electrodes is supported by an insulated post, preferably-of glass, in order that ionization may not take place between the leads. The leadsextending to the exposed portions of the other electrodes of the tube are also protected by insulating material in like manner.

Mounted within the ionization rings of the anode and cathode is a control electrode 7 which may be in the form of a wire helix the convolutions of which are interconnected by the metal post on which it is supported. If desired the interior of the helix may be shielded by at least one metal disk 8 and possibly by one at each end of the helix. If such a disk is used at the bottom of the helix then for the sake of practical structural design the disk will have a hole in the center thereof through which a work anode 6 may be interjected. This work anode may be in the form of a short wire located centrally with respect to the other electrodes.

Fig. 2 shows a modified tube structure in which the cathode 4a of the ionizing circuit may be in the form of a small disk, or. if desired, it may be a solid cylinder. The anode 5a of the ionizing circuit may be in the form of a rod or wire or it may have any other suitable structure. It is often desirable, though not essential, that its exposed area should be less than that of the cathode 4a. The work anode 621 is disposed suitably as a target toward which an excess of negatively charged-ions and electrons may be projected or attracted. A control electrode 7a which may have any one of a great variety of shapes and structures is interposed between the electrodes 5a andfia. In the embodiment of the control electrode shown in Fig. 2 there is a sheet metal cylinder across one end of which may be mounted 'a screen portion preferably having a very open used to adjust this potential.

- reaches the anode 6a.

tion generator is-obtained.

mesh. The cylindrical portion serves the purpose of shielding the work anode 6a from a partial bombardment by stray electrons which might not enter the interior of the cylinder through the mesh of the screen portion. The object of the structure will clearly be seen to direct the ions and electrons in such pathsas will be controlled as when they pass through the open mesh. It is therefore preferable that the work anode So should be at least partially surrounded by a shielding portion of the control electrode.

The tube of Fig. 2 is illustrated in connection with a circuit diagram in order that its manner of operation may be more clearly described. The same circuit diagram is also applicable to the tube of Fig. l.

The ionizing electrodes may have impressed upon them any suitable voltage from a source 9 feeding through a protective resistance 10. If the tube is to be used as an amplifier, the input voltages may be derived from a transformer 11 and the input circuit may be tuned in the usual manner by a variable condenser 12. If the input coil is coupled back to the output coil an oscilla- In order that the potential of the control electrode 7a may be adjusted to a suitable value, I may use a potentiometer 13 which is placed across the ionization prongs of the tube. The movable contact 14 is adjusted so that this control potential will be negative with respect to that of the ionization electrode 5a. A path of low impedance to variable currents impressed upon the control electrode 7a is not readily afforded by the potentiometer l3 nor by the source of energy 9 and therefore I provide, preferably, a small condenser 15 which shunts these elements.

The output circuit is seen to be coupled by a transformer 16 with the circuit which includes the work anode 6a and the ionizing electrode 5a. Potential of suitable value is impressed upon work anode 6a through a tap 17 which is taken off of the protective resistance 10 and preferably through an adjustable resistance 18 which can be The variable current may be shunted around the relatively high resistance path of resistances 10 and 18 by the use of a condenser 19.

The operation of either of the tubes thus far described when connected in a circuit such as that shown in Fig. 2 is as follows:

The field of ionization set up by the constant potential applied to electrodes 4a and 5a causes a stream of negatively charged ions and electrons to be shot through the convolutions of the control electrode 7a. The variable potential applied to the control electrode from the t'uned input circuit causes this stream to be electrically controlled so that more or less of the negative charge The energy drawn from the source 9 through the anode 6a is thus controlled by the behavior of the stream of ions and electrons. This current passing through the primary of transformer 16 delivers power fluctuations in the output circuit which are greatly amplified compared with the fluctuations of the input energy derived from the secondary of the transformer 11.

With the arrangement of the potentiometer l3 and the adjustable tap 17 on the resistance 10, I may, if desired, operate the tubes of this invention with a very low internal output-impedance. In other words, the voltage applied to the electrodes of the work circuit may be very small. Furthermore, the drop of potential between the work anode 6a and electrode 5a may be adjusted to such a value that at certain potentials of the control electrode the current in the output circuit varies very considerably. Under certain circumstances it may be desirable to introduce into the tube what I term an accelerating electrode 21 as shown in Fig. 3. This electrode may be in the form of a ring, either of wire or metal ribbon which is mounted between the control electrode 71) and the ionizing anode 5a. In some cases I have placed the auxiliary electrode 21 between electrodes 6a and 7b. The potential to be applied to the accelerating electrode 21 may be slightly more positive than that of the ionizing anode 5a and considerably more negative than that of the output circuit anode 6a. The large opening in the electrode 21 makes it possible for a considerable stream of electrons to be shot through the work anode 6a and the loss of efficiency due to the attraction of some ions and electrons to the electrode 21 itself is reduced to a minimum. With proper adjustment of the negative bias on the control electrode '7b this accelerating electrode 21 greatly improves the efiiciency of the control electrode. found useful to make the electrode 21 more negative than the ionizing anode So so as to repel and deflect the negative ions and electrons. In this way a very desirable increase in the effectiveness of the control electrode is obtained.

Referring now to the circuit diagram of Fig. 3,

Under certain circumstances it may be it will be noted that since the tube has five elements it is found convenient to apply the proper voltages to each of them by means of a potentiometer 22 which is placed across the full voltage of the source of energy 9. The protective resistance 23 for the ionizing circuit is here shown bethe potential of the ionizing anode 5a it will be seen that a more negative tap 24 supplies a suitable negative bias to the control electrode 7b while a more positive tap 25 renders the accelerating electrode 21 attractive to the stream of negatively charged ions and electrons in the direction of the work anode 6a the latter having the most positive potential of all the electrodes. The adjustable resistance 18 and primary winding of the output transformer 16 are also in circuit with the Work anode 6a. The input transformer 11 and output transformer 16 occupy the same relative positions in the circuit diagram as shown in Fig. 2. The bypass condensers 15 and 19 also afford a low impedance path for variable currents compared with that of the potentiometer 22 and resistance 18. In view of the foregoing description the operation of the tube as shown in Fig. 3 will be readily understood.

The behavior of the tubes of my invention may be more readily understood by reference to Figs.

5 and 6 which show one example of the actual relationship found to exist between the input and output circuits and the power gain to be derived. The values shown in the diagram are to be understood as illustrative only, since they have reference merely to the measurement of the characteristics of one particular tube. Other tubes made in accordance with my invention. might show characteristics which depart considerably from those shown in the diagram. Accordingly I have found that with an ionizing current of ten milliainperes and with 67 volts impressed upon the work-circuit anode 6, there being a load resistance R of 10,000 ohms in series with the source 26, the power gain in the work-circuit can be curves I and Ib for different voltages applied to the control electrode 7.

The transformer 11 can, as usual, be made to vary the input voltage by an amount represented as AEc. The steady control current characteristic L: is essentially a horizontal curve over a considerable voltage range so that the dynamic input resistance an, A1,

is very high. The slope of the curve It representing the output current is at the same time very steep. A test of one of the tubes of my invention showed at the operating point indicated in Fig. 5 a ratio Al? TI,

and a power gain that was 1225 fold. It will thus be seen that the tubes of my invention have an extremely, satisfactory performance characteristic for use in an amplifier.

It will be understood that many modifications of my invention are comprehended within the spirit and scope thereof and although I have shown but three species of an electrical discharge tube, my invention is limited only in accordance with the scope of the appended claims.

I claim:

1. An ionic glow discharge tube containing gas and comprising a non-thermionic cathode, an ionizing anode having its exposed area of activation small relative to that of the cathode, an auxiliary electrode at least partially surrounding 2.An ionic glow discharge tube containing a vapor and comprising, a non-thermionic cathode, an' ionizing anode having its exposed area of activation small relative to that of said cathode, an auxiliary electrode at least partially surrounding the main field of ionization, a control electrode more remote from said anode than said auxiliary-electrode, a work anode at least partially surrounded by said control electrode and an output circuit for said tube connected to said work anode.

3. Anionic glow discharge tube containing a vapor and comprising, a non-thermioniccathode, an ionizing anode, an auxiliary electrode at least partially surrounding the main field of ionization, a control electrode more remote from said anode than said auxiliary electrode, a Work anode partially surrounded'by said control electrode and an output circuit for said tube connected to said work anode.

- 4. An ionic glow discharge tube containing a vapor and comprising, an ionizing cathode, an ionizing anode, an auxiliary electrode, a control electrode more remote from said anode than said auxiliary electrode, a Work anode partially surrounded by said control electrode and an output circuit for said tube connected to said work,

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