US1945041A - Discharge tube for amplifying electric oscillations - Google Patents

Description

Jan. 3, i934. HQLST 3,945,641

DISCHARGE TUBE FOR AMPLIFYING ELECTRIC OSCILLATIONS Original Filed Nov. 2 1927 \NVENTOR G/LLES HOLST GEN ,1 a v I ATTORNEY Patented Jan. 30, 1934 UNITED STATES DISCHARGE TUBE FOR AIWPLIFYING ELECTRIC OSCILLATIONS Gilles Holst and Bernardus D. H. Tellegen, Eindhoven, Netherlands, assignors to N. V. Philips Gloeilampenfabrieken,

Eindhoven, Netherlands, a limited-liability company of the Netherlands Original application November 25, 1927, Serial No. 235,504, 14, 1926. Divided and and in the Netherlands December this application February 23, 1933. Serial No. 658,078

11 Claims. (Cl. 250-275) This application is a division of our copending application, Serial No. 235,504, filed Nov. 25, 1927. In that application we have disclosed and claimed circuit arrangements for the amplification of electric oscillations by means of thermionic devices. The present application has particular reference to the thermionic devices therein disclosed, and the claims herein are particularly directed to these devices per se.

It is known that when these devices are to be used for amplifying purposes .it is desirable that the slope of the grid voltage-anode current characteristic should be steep. With the customary triodes the steepness of the static characteristic decreases to an appreciable extent when oscillations are impressed on the control grid because these oscillations are transferred to the anode amplified, but in opposite phase, so that when the grid potential increases the anode current will on the one hand increase under the influence of the said increasing potential but the current will on the other hand decrease under the influence of the falling anode potential caused by the increased current flow so that the resulting increase of the anode current is diminished. In order to obviate this disadvantage with the final amplifier a so-called screening grid may be used between the control grid and the anode, said screening grid being maintained at a constant and fairly high positive potential, whereby the possibility remains of applying an appreciable negative grid bias to the control grid, which is very desirable in connection with the comparatively large output energy of the final amplifier.

If, however, a so-called final valve is used in an amplifier the phenomenon occurs that when the anode potential decreases, the screening grid current increases at the expense of the anode current and that when this potential fall becomes so large that the anode potential is less than the potential of the screening grid, secondary electrons will pass from the anode to the screening grid while part of the primary electrons which reach a position between the screening grid and the anode will reverse their direction, and return to the screening grid. These phenomena result, some to a greater extent and others to a smaller extent, in the screening grid current increasing at the expense of the anode current so that the advantage incidental to the use of the screening grid is again largely lost.

The invention is based on the recognition of the just mentioned phenomena and consists therefore in providing means which ensure that when the anode potential falls the increase of the screening grid current at the expense of the anode current will be substantially avoided. At the present state of knowledge it is. possible to suggest various means by which this object can be attained, said means being therefore also included in the invention. Some of these means, which on account of their simplicity and efficacious effect are particularly advisable, are the following:

1. The screening grid and the anode of the final amplifier have arranged between them an auxiliary grid kept at a constant potential which is not materially higher, preferably even lower, than the lowest instantaneous value of the anode potential.

2. A discharge tube, having at least two auxiliary electrodes between the cathode and the anode, is used as the final amplifier, the distance between the anode and the outermost auxiliary electrode being such that any electrons coming 75 from the anode are prevented from passing to the said auxiliary electrode because of the space charge of the auxiliary electrode.

3. A discharge tube is used having at least three auxiliary electrodes between the cathode'and so the anode, the auxiliary electrode on the anodes side being electrically connected to the cathode. This electrical connection can be provided within the tube.

4. A discharge tube having at least two auxiliary electrodes between the cathode and the anode is used as the final amplifier, the anode comprising a number of partitions directed radially with respect to the cathode. In this construction of the discharge tube which is described and claimed in our other divisional application, Serial No. 235,504, filed Nov. 25, 1927, the auxiliary electrode nearest the anode is preferably made of a number of conductors positioned parallel to the cathode and so that each conductor is located in a plane with one of the anode partitions and the cathode.

5. A discharge tube, having at least two auxiliary electrodes between the cathode and the anode, is used as the final amplifier, and in which the auxiliary electrode nearest the cathode screens 100 the next following auxiliary electrode against the electrons coming from the cathode. For this purpose the first mentioned auxiliary electrode may be formed of a number of small fiat ribbons.

6. A discharge tube having a screening grid, is 105 used as the final amplifier, the said screening grid being in turn screened by an auxiliary grid in its proximity and nearer the anode, said auxiliary grid being electrically connected to the anode.

The invention will be more clearly understood by reference to the accompanying drawing in which some circuit arrangements and tube constructions according to the invention are diagrammatically illustrated by way of example. In the said drawing:

Figure 1 shows a circuit arrangement according to the invention in which the final amplifier is provided with an auxiliary grid between the screening grid and the plate, the saidauxiliary grid being maintained at a constant positive potential.

Figure 2 is a diagram showing the potentials of the various electrodes of the final amplifier shown in Figure l.

Figure 3 shows a circuit arrangement corresponding to that shown in Figure l, the difierence being inter alia that the auxiliary grid is electrically connected to the cathode, and

Figure 4 shows diagrammatically a preferred construction of the discharge tube which in accordance with the invention should be preferably used as the final amplifier.

Referring to Figure l the secondary of a transformer 1, has one end connected to the control grid 2 of thefinal valve and its other end is connected through a grid bias battery 7 to the negative end of the cathode 6. In addition the dis: charge tube comprises a screening grid 3 which is connected to such a point of the high tension battery 9 that it is kept at a high positive potential which, however, is slightly lower than the average potential of the anode 5 In the circuit of the anode 5 is included a reproducer 10 (telephone, loudspeaker, recording set or the like). The cathode 6 is supplied from a battery 8 which may be connected across a variable resistor. Between the screening grid 3 and the anode 5 is arranged an auxiliary grid 4 which is connected to such a point of the battery 9 that the potential of 4 is materially lower than that of the screening grid 3.

In the diagram shown in Figure 2, 2, 3, 4 and 5 are graphically plotted so as to give a better idea of the distribution of the electric field within the discharge tube. The potential of the auxiliary grid 4 should be so little positive that it can be assumed with all reliability that the instantaneous anode tension never falls materially below the potential of 4, even not with maximum potential amplitudes on the control grid 2. Therefore any secondary electrons emitted by the anode are absolutely prevented from passing'to the auxiliary grid 4 because the potential of 5 is so much greater than that of 4 that the strength of the field, due to the potentials, increases continuously and rapidly from grid 4 to anode 5.

The circuit arrangement may be slightly simplified by connecting the auxiliary grid 4 directly to one of the ends of the filament 6, as shown in Figure 3. The auxiliary grid 4 consequently has a zero potential so that the same remarks made above in connection with the secondary electrons from the anode apply in this case. Inaddition it is possible to directly connect the grid 4 to the cathode within the valve as shown in Fig. 4, or, if desired, within the cap. Thus the number of the contact screws or pins to be fitted on the valve is decreased by one.- A second difierence between the structure of Figure 3 and that of Figure 1 is that the screening grid 3 is connected to the posi 've end of the battery 9 and thus receives the same direct current potential as the anode 5. The output of the final valve is thereby increased.

Figure 4 shows the principal elements of a tube electrodes located between constructed according to the invention in which the cathode and the anode have arranged between them three auxiliary electrodes, the outermost of which is electrically connected to the cathode within the tube. In this construction the various electrodes are sealed in a well-known manner,

.with some of the carriers serving also as leadingin wires, in the glass squeeze or press 13 of a stem 14.

The cathode 6 is formed by a taut wire or filament which is stretched between two carriers 11, the left hand one of which is lengthened upwardly and connected electrically at the top to a small metal beam 12 which in addition to the lower metal beam 22 serves to stiffen and support the outermost grid 4. This grid serves as an auxiliary grid in the sense of the invention and is arranged between the anode 5 and the screening grid 3. From Figure 4 of the drawing it will be observed that the turns of wire of the auxiliary grid 4 are more widely spaced than those of the screening grid 3; in other words, the former grid is of more open mesh than the latter grid. The screening grid is supported in a well known manner by a small carrying beam 20 and by two carriers 21 sealed in the squeeze or press 13. The right hand carrier is led out through the squeeze. Finally the screening grid 3 and the cathode 6 have between them a control grid 2 which, similarly to the two grids 3 and 4, is shown as a helically wound wire attached on the lower side to a small carrying beam (not shown) which is supported by means of two carriers 23 sealed the squeeze 13. The control grid carrying beam which may be similar to those for the screen grid 3 and auxiliary grid 4 is not illustrated for the sake cl simplicity. The left hand carrier of the two last mentioned carriers is led out through the squeeze. The anode 5 is supported in a well known manner by a stitl central carrier 24 which is sealed in 115 the squeeze 13 and led out through this squeeze. There are therefore in the aggregate five leadingout wires, tour of which may, for example, be connected to contact pins at the bottom of the cap, whereas the fifth one, for example the leadingout wires of the screening grid, may be led to a contact screw (not shown) on the cylindrical side wall of the same cap.

With the invention it is possible to use a final amplifier having a large power output and an internal resistance which is so large as compared with the impedance of the reproducer (loudspeaker or the like) that the current variations through the reproducer follow exactly the potential variations of the control grid of the final valve 1 0 so that the reproduction is undistorted.

In summary, the invention therefore comprises means used either separately or in combination, with a final amplifier having a screening grid between the control grid and the anode by which 135 the screening grid current is prevented entirely or partially from increasing at the expense or the anode current when the anode potential falls.

What we claim is:

1. A discharge tube having a filamentary cath- 14o ode, a control grid and an anode, a screening grid interposed between the control grid and the anode, characterized in that the screening grid, on the anodes side, is substantially screened by an being directly electrically connected inside the tube to the cathode.

2. A discharge tube having cathode, control grid and plate electrodes comprising two auxiliary the control grid and posed between the cathode, and the anode, thegrid electrode nearest the anode being directly connected to one end of the cathode within the evacuated envelope.

4. An electron discharge tube comprising an evacuated envelope having mounted therein an electronemitting cathode, a control grid electrode disposed around the cathode, a screen grid electrode disposed around the control electrode,

an auxiliary grid electrode disposed around the screen electrode and directly connected to the cathode within the envelope, and a plate electrode disposed around the auxiliary grid electrode.

5. An electron discharge tube comprising an evacuated envelope having mounted therein an electron emitting cathode, cylindrical control, screen and auxiliary grid electrodes and a cylindrical plate electrode, all concentrically arranged about the cathode in the order named, and a direct electrical connection within the envelope between one end of thecathode and the auxiliary grid electrode.

6. An electron discharge tube comprising an evacuated envelope provided with a reentrant stem, a plurality of electrodes, including a cathode, control grid, screen grid, auxiliary grid and anode, contained within the envelope, supporting arms carried by said stem for supporting the cathode, and an electrical connection from said auxiliary grid to one of said cathode supporting arms.

7. An electron discharge tube comprising an evacuated envelope provided with a reentrant stem, a plurality of electrodes, including a cathand said anode and electrically ode, control grid, screen grid, auxiliary grid and anode, contained within the envelope, supporting arms carried by said stem for supporting the cathode, one of said cathode supporting arms being extended beyond the point of connection to the cathode, and an electrical connection from the auxiliary grid to said extended portion of said cathode supporting arm.

8. An electrical discharge device comprising a sealed envelope containing an electron emitting cathode, an anode, three grid electrodes positioned to be successively passed by the discharge between said cathode and said anode, and a direct electrical connection between said cathode and said grid electrode adjacent said anode.

9. An electron discharge device comprising an electron emitting cathode, an anode, a screen grid between said cathode and said anode, a control grid between said screen grid and said cathode, and an additional grid between said screen grid connected to said cathode whereby said additional grid is maintained at substantially the same potential as said cathode.

10. An electron discharge device comprising an electron emitting cathode, an anode, a control grid adjacent said cathode, a screen grid between said control grid and said anode, an additional grid of more open mesh than said screen grid mounted between said screen grid and anode and having an electrical connection to said cathode whereby said additional grid is maintained at zero potential with reference to said cathode.

11. An electron discharge device comprising an electron emitting cathode, an anode, a control grid adjacent said cathode, a screen grid between said control grid and said anode, an additional grid of more open mesh than said screen grid mounted between said screen grid and anode and having a direct electrical connection to said cathode within the device whereby said additional grid is maintained at substantially the same potential as the cathode.

GILLES HOLST. BERNARDUS D. H. TELLEGEN.

CERTIFICATE OF CORRECTION.

Patent No. 1,945,041.

January 50, 1954.

GILLES HOLST, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

after the numeral and period "14. insert the following sentence:

1' is the glass bulb to which the stem is sealed.;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

(Seal) Signed and sealed this 15th day of December, A. D. 1956.

Henry Van Arsdale Page 2, line 84,

Acting Commissioner of Patents.

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