US2056872A - Electron discharge device - Google Patents

Description

Oct. 6, 1936. K. STEIMEL ELECTRON DISCHARGE DEVICE Original Filed June 29, 1934 2 Sheets-Sheet 1 .INVENTOR KARL STEIMEL ATTORNEY K. STE IMEL 2,056,872

ELECTRON DISCHARGE DEVICE 2 Sheefs-Sheet 2 Original- Filed June 29, 1954 III lllllllllll d-------v LM' 27 INVENTOR KARL STEIMEL BY \TTQRNEY manner as the distant signal.

Patented Oct. 6, 1936 PATENT OFFICE ELECTRON DISCHARGE nnvron Karl Steimel, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m..b. H., Berlin, Germany, :1.

Germany corporation of Original application June 29, 1934, Serial No. 732,991. Divided and this application June 20,

1935, Serial .No. 27,490

3 Claims.

My invention relates to an electron discharge,

tube of the multi-grid type and having a plurality of discharge paths extending from the cathode, each discharge path being at least partially controlled by a common control electrode, and is a division of application Serial No. 732,991, filed June 29, 1934.

In radio receivers employing the superheterodyne method of reception, the problem is to combine two different oscillations; that is, the oscillations produced by a distant signal received by the antenna and usually amplified in a preceding stage, and the local oscillations produced in the receiver proper for providing the heterodyne action, so that the resulting intermediate frequency oscillations are modulated in the same This action is usually accomplishedin a so-called mixer tube used in various well known circuits. In order to simplify the receiver, it has been previously proposed to provide the function of the local oscillator (heterodyne) and that of the mixer stage within a single tube. This is usually accomplished by using a tube containing several rid electrodes between a cathode and an anode. Upon one of the grids, for example, that next to the cathode, the modulated distant signal may be impressed. By means of two further grids coupled to each other usually by a feed back arrangement, the local heterodyne oscillation is produced, and the latter together with the received signal results in the desired intermediate frequency oscillations which appear in the anode circuit.

It is important to generate the local oscillations independently of control by the input or signal voltage. To this end, a screen grid is placed between the control grid and the electrodes serving for the production of the local oscillations. In this way a tube having six electrodes (hexode) is obtained, which has posi-' for example, for the purpose of compensating.

for fading phenomena due to atmospheric conditions. In this case, the electron current is eventualh blocked to such an extent, by the action of the control electrode, that the current density necessary for the production of thelocal oscillations, is no longer available.

Similar conditions exist in other circuits. This is true, for example, in a high frequency amplifier stage made regenerative for example by means of feed back, and whose amplification factor is controlled at the same time by varying the grid voltage. Also the scalled homodyne circuit must be mentioned in this connection. As is well known this circuit is characterized by the heterodyning of the received signal on an oscillation produced in the receiver and of a frequency conforming with that of the carrier wave. These last two arrangements differ from the above mentioned mixer circuit in intermediatefrequency principally by the value of the frequency with which self excitation or regeneration is produced.

It is an object of my invention to provide an improved tube which will avoid the above disadvantages, particularly if the tube is used for volume control and which has a more favorable electrical separation between the parts of the tube generating the local oscillations and the parts performing the actual mixing operation by "constructing a tube having two separate distwo electrode systems adjacent each other, and

to conductingly connect, or toc'onstructively join one of the electrodes or several of the electrodes in the. different systems. The present invention differentiates over the arrangement described in that the two discharge paths are not placed side by side, but extend in different directions, preferably displaced 180 to each other. This provides the advantage of a more favorable condition for less coupling of the two systems without the use of special shielding devices, and the further advantage that a short length construction of the tube is obtained, in view of which the electrode system .can be easier manufactured and mounted. Furthermore, such an electrode sysverse cross section taken through a tube made in accordance with my invention and showing the electrode arrangement." Figs. 4 and 5 are schematic transverse cross sections of modifications of the tube shown in Fig. 3. Fig.6 is a diagrammatic, showing of a circuit embodying a still further modification of the tubes shown in the preceding figures.

a glass bulb or envelope I, containing an electron emitting cathode 2, which may be directly or indirectly heated. The cathode is enclosed by a grid like electrode 3 preferably of cylindrical shape. The other electrodes are positioned in different current paths. The auxiliary anode 4 is placed on one side of the cathode and grid 3 and on the other side is placed the screen grid 5, the control electrode 6, a.v second screen grid 1 and the main anode 8.

With a tube of the type described the circuit shown in Fig. 2, as well as others, can be used. The input circuit comprising the inductance L and condenser C fed from the antenna A or from a preceding stage, is connected between the oathode 2 and the control grid 6, which is negatively biased by means of the battery E If it is desired to provide automatic volume control, the control grid bias may be made variable and to depend upon the input amplitude in any well known manner. Inthis case the grid 5 ,is designed to have a variable mu or amplification factor.

- The two screen grids I and I may be operated at the same positive bias. They are electrically connected to each other within the envelope or within the base thereby saving one base pin. The

auxiliary anode 4 connected to the positive side of the anode battery E. through'the inductance 50 L, is coupled by means of this inductance to the tuned circuit comprising inductance L and condenser Cl connected in the circuit of grid 3. Since the grid 3 is in the main current path between the cathode 2 and the main anode 3, the discharge current between the cathodes and the anode I will be controlled by the grid 3 to vary the frequency of oscillation produced in the auxiliary discharge circuit, and at the same time will be controlled by he signal impressed on the control grid 3. Regarding the operation of the tube, it is pointed out that the voltage of the electrode 3 controls the current distribution between the anode 3 and the first screen grid I. In other words, the mutual .conductance S or steepness of the anode current characteristic will be affected by the voltage on electrode 8. Since the presence of the second screen grid I makes reaction of the alternating anode potential upon the control performance so slight that it can be disregarded, the condition exists that the alternatingplate currentJsisequal totheproduct of'the heterodyne voltage Eu (local oscillator voltage) impressed upon grid 3 and the mutual conductance S (that is J=SE"). Since, however, 3 is 75 also a motion of E (E =alternating input volttem is practically free from microphonic effects.

As shown in Fig. 1, the tube is provided with age), the heterodyne voltage Eu and the input voltage E; have a multiplying effect upon the discharge current. In this way there is formed the sum and difference of the frequency of input wave or signal and the heterodyne frequency, 5 which appearsin the anode circuit and is transferred to the subsequent amplifier, which may be connected across the oscillatory circuit comprising inductor L2 and condenser C: tuned to the intermediate frequency.

In the oscillatory grid circuit L1, there is connected in series with the coil Li, a resistor R bridged by a condenser C; for the following reason: It is desirable to be able to readily initiate the heterodyne oscillations and at the same time it is necessary to maintain the amplitude of the oscillations at a constant value. The resistor R performs both of these functions. Before oscillation starts, grid 3 is at cathode potential, and since the steepness of the grid voltage plate current curve is the greatest under these conditions, oscillations are easily built up. As soon as the oscillations are generated, a'grid current producing a voltage drop across resistor R, begins to fiow, and consequently the working point or grid bias of the tube will be shifted into the region of negative grid bias thereby stabilizing and limiting the amplitude of the oscillations.

It may furthermore be of advantage to provide the two halves of grid 3 with a different mu or amplification factor. For producing oscillations a high mu is desirable since in this case small feedback voltages suffice, and the steady state oscillation amplitude can be adjusted to have small values, especially by means of the action of the resistor R mentioned above. However, for the other discharge path the total useful control range is of great importance. This range must be large as compared with the total useful control of the discharge path serving fonthe production of local oscillations, in order that the heterodyne oscillations do not cause overload and produce distortions, which distortions must be avoided under all conditions because of'thempper'harmonics thereby developed. For this reason different values of mu (amplification factor) are chosen for the two grid halves. The mu at the side of the local oscillation system is made from to times as large as the mu at the side of the mixing system.

The mu meant is that with reference to the electrode directly following the respective grid half, thus in the one case, to the run between electrodes 3 to l, and in the other case between electrodes 3 to I. The requirement of a different mu is especially easy to accomplish if the grid 3 is vcomposed of two halves which are conductingly connected to each other, since in this case the current penetration (determined by the width of the mesh or the pitch of the grid) as well as the distance from the cathode can be made of different magnitude.-

Fig. 3 shows a transverse cross section of the electrode system constructed in accordance with my invention. In the glassenvelope I there is placed the cathode 1, preferably indirectly heated, and enclosed by a concentric cylindrical grid 3. In order to bring the grid surface as close as possible to the cathode surface. it is shaped as shown and is secured to the supporting rods l I by means of two ribs or fins Ill. By-this construction the production of a homogeneous field is made possible in the proximity of the cathode. At the same time, the ribs or fine II, which act as shields. im-

- prove the decoupling of the two discharge paths by their shielding action. Theauxiliary anode 4,. having the shape of a fiat or curved plate, is placed the main anode 8. These electrodes are formed for example, as plane surfaces parallel to each other. Since, as stated above, the two screen grids 5 and I can have the same potential applied to them, they can be structurally combined, and may for example have the shape of a box formed of a metal mesh, and be mounted on two longitudinally disposed parallel supports l2.

Within this box is arranged the control electrode 6 supported by two columns. ll. In order to pre-v vent a deviation of the electrons in the direction of the supports II, the columns B are formed of solid sheet metal strips.

' flat cathode is that a very homogeneous field dis- -tribution is formed around it, and that the control electrode can be very closely disposed to the cathode because it can be stretched out between the supporting wires. In addition the flat cathode insures a favorable decoupling of the two discharge paths. The control grid 22 has the shape of 'a box of rectangular cross section, formed of two halves having a different width of the mesh. The same box shape is also used for the double screen grid 23 whose surface is twice passed bythe discharge current. The second control grid 24, as well as the anode 25, has a U-shaped cross section, which promotes the formation of a homogeneous field and permits the electrodes to be mounted in the center plane 'of the electrode system. The auxiliary electrode 26 is shaped as a flat plate.

The modification shown in Fig. 5 shows the electrode system provided with a suppressor grid. For the sake of simplicity the same reference characters have been used for the electrodes corresponding with those of Fig. 4. The added suppressor grid 21 performs several functions. A negative potential with respect to the anode 25, preferably the cathode potential, is applied to the suppressor grid. Because of this, the suppressor grid prevents secondary electrons from the anode from reaching the preceding screen grid 23. At the same time, the mu of the control grid 22 with respect to the anode 25 is increased and therefore the anode reaction is decreased, 1. e. the plate impedance is increased.

The suppressor grid furthermore permits the application to the screen grid 23 of the same direct voltage as that applied to the anode 25, while heretofore a lower voltage was usually impressed upon the. screen grid. this voltage ordinarily being obtained from a voltage divider. As shown in Fig. 5, the suppressor grid is likewise formed into a box shape and surrounds theauxiliary electrode 26, thus including the discharge path between the cathode and the auxiliary anode. Consequently a favorable screening towards the outside is produced, so that the discharge is no longer influenced by disturbing exterior fields.

A further embodiment of a tube-coming within the scope of the present invention, is schematically represented in the circuit diagram of Fig. 6. For the sake of simplicity, identical reference characters have been used here for the elements conforming with those in Fig. 2. The novel feature in the tube is in that the two halves 3', 3" of the innermost grid 3 are not conductlngly connected to each other, but capacitively by means of a condenser K. The condenser is'suitably mounted in the interior of the tube or in the socket, .and each grid half is provided with-an insulated lead. This measure appears-to be expedient, where the two halves 3', 3" although having the same alternating voltage applied to the two halves, have diiferent direct voltages applied to them. This case occurs when the innermost grid 3' is intended to be used for volume control. The high frequency voltage supplied by the input circuit LC is'impressed upon the control grid'6 only, while the variable control voltage source designated by Er is applied to the grid half 3' as well as to the second control grid, or the control voltage may be applied only to the grid 3'.

In the first case, the controlling action will be more efiective. In the lead to the grid half 3', a. resistance W is inserted, in which the same rapid frequency voltage will be developed as that in the tuned circuit L1, Cl- By exchanging the leads to the grid halves 3, 3", it is possible to place the resistance W inside the tube, and to conmeet the same to the grid half 3" and to the cathode, so that a special lead to the grid 3" can be dispensed with.

While I have indicated the preferred embodiment of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it

is apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim is: a

1. A circuit including in combination an electron discharge tube having a thermionic cathode,

' a grid electrode surrounding 'said cathode, a main anode positioned on one side of said cathode, a control electrode between said main anode and said cathode, and a box-shaped grid electrode surrounding said control electrode, an auxiliary anode placed on the opposite side of said cathode from said main anode, means for impressing an alternating voltage of predetermined frequency said cathode, a box-shaped grid electrode surrounding said control electrode,.an auxiliary anode placed on the opposite side of said cathode from said main anode, means for impres ing an alternating voltage of predetermined frequency between said auxiliary anode and the grid surrounding said cathode, meansfor impressing an alternating input voltage of a different frequency between said cathode and the control electrode whereby an alternating voltage of in-. termediate frequency is obtained on the main anode, a circuit connected to said main anode,

and a resistor bridged by a condenser inserted in the lead between the cathode'and the grid electrode surrounding said cathode.

3. A circuit including in combination an electron discharge tube having a thermionic cathode, a grid electrode surrounding said cathode, a main anode positioned on one side of said cathode. a control electrode between said main anode and said cathode, and a box-shaped grid electrode surrounding said control electrode, an auxiliary anode placed on the opposite side of said cathode from said principal anode, means for impressing an alternating voltage of predetermined irequency between said auxiliary anode and the grid surrounding said cathode, means for impressing an alternating input voltage 0! a diflerent frequency between said cathode and the control electrode whereby an alternating voltage or intermediate frequency is obtained on the main anode. a circuit connected to said main anode, and a resistor bridged by a condenser inserted in the lead betweenthe cathode and the grid surrounding said cathode, and means for impressing a bias upon the grid surrounding the cathode dependent upon the amplitude of the alternating input voltage.

KARL STEIlidEL.

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