US2417805A - Electric oscillation generator and amplifier - Google Patents

Description

March 25, 1947. BANARD T 2,417,805

ELECTRIC OSCI LLATION GENERATOR AND AMPLIFIER Filed May 12, 1942 3 Sheets-Sheet l Fig. 3. K

ATTOIPIVEV March 25, 1947. A N ETAL 2,417,805

ELECTRIC OSCILLATION GENERATOR AND AMPLIFIER Filed May 12, 1942 3 Sheets-Sheet 3 To VI. dhd R3 as Fig.3.

72, V1.and R2 85 F73.

Patented Mar. 25, 1947 UNITED STATES ATENT QFFICE ELECTRIC OSCILLATION GENERATOR AND AMPLIFIER Application May 12, 1942, Serial No. 442,636 In Great Britain April 30, 1941 14 Claims.

The present invention relates to the improvement of electrical oscillation generators for very high frequencies, and particularly to cases in which a high degree of stability of operation isrequired.

The usual methods hitherto used in this field have become increasingly unsuitable as the frequencies which have to be dealt with are increased. In particular, difiiculties have been encountered, for example, even in the relatively low range from 1000 to 5000 kilocycles. The interelectrode capacities of the amplifying valves used in the circuits constitute serious limitations to the amplification which can be obtained at these frequencies, and increase the difficulties of obtaining satisfactory amplification and phase shift frequency characteristics. In order to avoid these inconveniences and to improve the stability of the circuit in the presence of variable external factors (for instance, temperature and power supply), it is desirable to restrict as far as possible the number of valves used in a given circuit, and this requires the use of valves having a high mutual conductance. Unfortunately valves of the ordinary type which have a high mutual conductance usually have the grid or grids very close to the cathode and accordingly they have generally a rather high grid-cathode capacity, which largely destroys the advantage which would otherwise be gained from the high mutual conductance.

The present invention is concerned chiefly with frequency ranges up to 300 megacycles, or more, and two classes of arrangements will be described, the first of which is suitable for frequencies not much higher than 30 megacycles, and the second is suitable for use over the whole range. The generating circuits commonly used hitherto usually require at least three valves of the conventional type which must operate at the oscillation frequency, while as will appear from the following description, the desired results may be obtained in the frequency range just specified with one valve only, operating at the oscillation frequency.

In the construction of orthodox amplifying valves, the physical sizes of the electrodes are largely controlled by the requirements set by the necessity of dissipating the heat generated by the rangements can be made whereby they dissipate only a small fraction of the total power dissipated in the valve, it becomes possible greatly to reduce their dimensions for a given mutual conductance. This would enable a corresponding reduction of the interelectrode capacities associated with the oscillating circuit to be made, so that a greater proportion of the circuit which actually determines the frequency may be outside the envelope of the valve.

It has been found that considerable simplification of the generating circuits, and also reduction of the interelectrode capacities associated therewith, can be obtained by the use of a known electron discharge device or multiplying valve, with or without certain modifications of the design and with certain special associated circuits. This results in greatly improved operating characteristics and stability in the frequency range mentioned above.

According to the invention, in an electrical oscillation generator, an electron multiplier valve is associated with an amplitude stabilized oscillating circuit so that one or more of the multiplying, electrodes participate directly in the generation of the oscillations. According to other features, the multiplying electrodes may be spaced apart from the source of electrons to reduce the heating effect, and this permits their physical dimensions to be reduced, in order to reduce correspondingly the interelectrode capacities.

The invention will be more clearly understood from a consideration of the following detailed description and, with reference to the drawings in which:

Figure l is a diagram of the abovementioned multiplying valve, together with a schematic of a suitable operating circuit.

Figure 2 is a block schematic of an oscillatory circuit.

Figures 3, 4, 5 and 6 are circuit schematics of stabilized high frequency oscillators, Fig. So being a schematic diagram of a concentric cable transmission line.

Figure '7 comprises curves which show certain operating characteristics of the multiplying valve.

Figure 8 is a diagram of a multiplying valve modified in accordance with certain features of the invention. 7

In the circuits given a number of condensers denoted K are shown. These are blocking condensers having a capacity sufiiciently high to form a coupling of negligible impedance. Likewise resistances marked G are leak resistances of high value, the shunt effect of which can be neglected.

A thermionic valve oscillator usually consists in essentials of an amplifier having a positive feedback path which must contain a frequency discriminating circuit. It is well known that the frequency is fixed by the conditions (a) that the gain of the amplifier shall be exactly equal to the loss through the feedback path, and (b) that the total phase shift round the loop includ-- ing the amplifier and the feedback path shall be zero. Stability of the frequency is dependent (amongst other things) on the constancy of the gain and phase change introduced by the amplifier, and in most known forms of oscillators it is practically impossible to achieve the necessary constancy of these factors so that the desired degree of frequency stability is obtained in the range of frequencies with which the present invention is mainly concerned.

An already known arrangement by which some improvement in stability may be obtained, is shown schematically in Fig. 2, in which Al is the amplifier and D is the discriminating circuit in the feedback path mentioned above. The circult of D may consist, for example, of a shunt anti-resonant circuit L, C, and a series resistance R, as shown. Connected to the input terminals of the amplifier Al is a controlling amplifier A2, the output of which is applied suitably to the amplifier Al through a rectifier W as indicated diagrammatically in Fig. 2, for the purpose of automatically controlling its gain. If it is assumed that the oscillations have built up to some stable level, and that at some subsequent period the gain of the amplifier A! should tend (for example) to increase, the level of the oscillations will tend to rise, thus also raising the level at the inputs of both the amplifiers. The control exerted on Al by A2 will be so arranged that the gain of Al tends to be reduced, and so the gain of the amplifier Al and also the level of the oscillations will be maintained practically constant. The operation of the arrangement when the gain of Al tends to become reduced will be opposite to that just described.

It should be added that the amplifier A2 could if desired be connected to the output of Al instead of to the input, and the operation would be similar.

Thus it will be seen that by this arrangement one of the causes of frequency variation will be eliminated, or at least reduced; unfortunately, howeverQit is difficult to construct an amplifier covering a frequency range of more than two or three octaves in which the phase shift remains substantially zero over the whole range, and further, electrical gain controlling arrangements usually introduce amplitude distortion. The present invention discloses means whereby these difficulties may be surmounted, so that the arrangement of Fig, 2 may be used up to frequencies in the order of 300 megacycles.

The means by which this is achieved is by the use of a modification of a known form of electron discharge device or valve which can be considered as equivalent to a triode in which an electron multiplying arrangement is incorporated between the control grid and the anode. Fig. 1 gives the details of a preferred form of this type of multiplying valve and includes an example of a circuit which may be used for supplying the necessary. potentials to the electrodes. indicates a very simple arrangement by which the valve may be operated as an amplifier.

It also The multiplying valve M is provided with a series of electrodes which have been numbered as indicated in Fig. 1. The first two electrodes, l and 2, are the cathode and control grid, respectively, and 8 is the anode proper of the valve considered as a triode. The plate 3, provided with a central hole, supplies the initial field for producing a stream of electrons from the cathode, a proportion of which pass through the hole. Behind the plate 3 is another plate 3a perforated with a large number of small holes, and coated on the side nearest the plate 3 with a material which produces a powerful secondary emission... The plates 3 and 3a are electrically connected. The electrons which pass through the hole in the plate 3 thus strike the plate 3a, and secondary electrons are produced, some of which pass through the holes and are accelerated by a grid 4, which also collects some of them, this grid being connected to a point of higher potential than the plate 3a. Behind the grid 4 is another secondary emitter plate 4a similar to 3a, and electrically connected to the plate 4. Behind the pair of electrodes 4, 4a, are located in succession three more exactly similar pairs 5, 5a; 6, 6a; 1, 1a; connected successively to points of progressively higher potential. Behind the secondary emitter la is the anode proper 8 already mentioned, which is also perforated, but is not a secondary emitter. The electrons which pass through the anode 8 strike a target 9 which is also a secondary emitter, and is connected to a point of lower potential than the anode 8, so that the electrons emitted therefrom will be attracted to, and be collected by, the anode. Thus it will be seen that the electron current produced by the electrodes l, 2 and 3 will be progressively increased or multiplied by the successive pairs of emitting and collecting electrodes. The final multiplied current collected by the anode 3 will be proportional to the original current and will be modulated in the same way by signals applied to the grid 2.

It should be explained that the collectors 5, 6 and l, in addition to accelerating the electrons arriving from the previous stage, also maintain a space charge which serves the purpose of reflecting back the secondary electrons produced by the following secondary emitter, so that they may be caused to travel forwards with the rest of the stream. The plate 3 will also be regarded as a collector electrode, since it operates substantially in the same way as the grids l, 5, 6 and 1. Further, the number of pairs of multiplying electrodes similar to i and 4a is not nezessarily limited to four. Additional pairs may be provided if further amplfication is desired.

This arrangement produces a high mutual conductance without, at the same time, producing a large capacity between the grid 2 and the cathode l, or between the grid 2 and the anode 8. In a valve of this type, a mutual conductance of about 40 milliamps per volt, and a slope capacity ratio about four times greater than w th a screen grid valve of the usual .typ may be obtained. It can be seen, therefore, that when using this multiplying valve it should be possible to construct an amplifier having a flat frequenzy characteristic over a range of perhaps four times that which can be obtained with an ordinary valve. t will be further noted that as the electron current is progressively increased by the successive pairs of multiplying electrodes, the power dissipated by each pair alsov progressively increases, so that only a small part of the total power will be dissipated by the pairs nearest to the cathode.

In Fig. 1 the various electrodes are'supplied with the required potentials by means of a potentiometer of series resistances Rl to R9, the junction points of which are connected to ground with coupling condensers K; and it will be noted that the electrodes i and la are at earth potential. This arrangement, however, is only one example of how the supplies may be obtained and it is not necessary that any particular pair of electrodes should be at earth potential. Fig. 1 also includes an example of a simple arrangement for adapting the valve as an amplifier. A pair of input terminals is connected one to the cathode I, and the other to the grid 2 through a condenser K; and an output transformer T is connected with the primary winding in series with the anode 3 and the secondary winding to a pair of output terminals. A signal applied to the input terminals will be obtained amplified at the output terminals.

A number of circuits or automatically stabilized high frequency oscillators in whizh a multiplying valve is used will now be described. Most of these circuits, however, may require that certain of the electrodes of the valve shown in Fig. l, which are there shown connected together, should be separated and brought out to separate terminals.

In Fig. 3 is shown an oscillatory circuit in which a tuned circuit consisting of an inductance LI and a condenser Cl is connected between the grid 2 and the cathode l of the valve M. The secondary emitter electrode 3a provides the required feedback through the resistance Rib. The electrode 3a must be disconnected from the plate 3, but is externally connected thereto by an impedance Z, designed to bring the eleztrode 3a to the same phase as the grid 2. This arrangement avoids the use of a transformer which is a major source of phase shift difficulties.

An ordinary triode valve Vi is connected with its plate-cathode circuit in parallel with the resistance R3 which determines the potential of the plate 3. The grid-cathode circuit of the valv V! is connected across a resistame RH which is in series with a rectifier W and fed from a winding of the output transformer T whose primary winding is in series with the anode 8 of the valve M. The resistance Rlil is so chosen that the feedback produced by the electrode 3a is just sufficlent to enable the circuit Ll, CI to oscillate. The amplified oscillations are obtained from the transforme T, and should there be a variation in the amplitude, the drop of potential across resistance RH will change and will accordingly change the plate current of the valv Vi. This will in turn change the potential applied to the plate 3 and thereby the secondary emission of 3a, and the subsequent amplification, and the con-- nections are so arranged that this change is in the direction which will tend to restore the oscillations to their original amplitude. The circuit is accordingly self-stabilized.

Th method of automatically controlling the gain of the amplifier, which has just been described, does not introduce any appreciable distortion as may be seen by referring to Fig. '7, in wh ch the multiplying factor of the valve M is shown plotted against the voltage per stage, and it can be seen that, provided a suitable operating point be chosen, the variation of the multiplication factor is substantially linear.

Other simple methods of controlling the gain of an amplifier (such as, for example, by the use 6 by means of the potential applied to a control"- ling grid) produce changes in the amplification which ar by no means linear.

In Fig. 3 the electrodes of M which are not directly concerned with the external oscillating circuit have been omitted for clearness, as also have been omitted the corresponding resistances of the supply potentiometer, their presence being indicated by a dotted line. They are, of course,

actually in use and are connected as shown in Fig. 1.

In Fig. 4 is shown a modification of Fig. 3 which though less simple and easy to control, has the advantage of allowing a multiplying valve M of the ordinary type, as shown in Fig. l, to be used without any modification of the electrode connections. In Fig. 4 the feed-back connection is made through another triode valve V2. The parts of the circuit which are the same as in Fig. 3 have been omitted and it should be assumed that they are connected in exactly the same way. In the case of Fig. 4, the electrodes 3 and 3a are connected directly together as in Fig. 1, and on this account the phase of 3a differs from that of the control grid 2 by very nearly degrees. Accordingly the feed-back connection between 3a and the oscillatory circuit Ll,

Cl must introduce a change of phase of 180 degrees. This is done by making the connection through the valve V2, the grid of which is connected to the electrode 3a and the plate to the resistance RH), as shown in Fig. 4. The impedance Z is connected in series with the common terminal of electrodes 3 and 3a, and, as in Fig. 3, is designed to adjust the relative phases of the grid 2 and electrode 3a, the right hand terminal of impedance Z being connected with the upper terminal of resistance R3 and to the plate of valve VI, as shown in Fig. 3. The cathode of valve M, Fig. 4, is connected with the cathode of valve VI and the lower terminal of resistance R3, as shown in Fig. 3, the grid 2 of valve M, Fig. 4, being connected through the inductance Ll with the lower terminal of resistance R2, as shown in Fig. 3. All the other electrodes 4 and 4a to 9 and their connections, the output transformer T, rectifier W, and resistances RH, forming a part of the Fig. 4 modification, but not shown in Fig. 4, are connected as in Fig. 3, as

' explained above.

The introduction of the reversing valve V2 in addition to complicating the circuit, adds a source of potential variation, and accordingly the arrangement of Fig. 3 is preferable if it can be used.

In Fig. 5 is shown another stabilized oscillator circuit particularly suitable for very high frequencies, and which can be used up to possibly 300 megacycles per second. This circuit requires that an early stage, such as the first, of the electron multiplier shall have the collector and secondary emitter isolated, and. also one subsequent stage, which is not the last. Accordingly, in Fig. 5, the pairs 3, 3a and 4, 4a are shown separated. The output arrangements and also the rectifier circuit are exactly the same as in Fig. 3, and are This will be seen to be a very well known type" of oscillating circuit, such as is frequently associated with a triode valve, and the electrodes of the valve M involved are, in fact, operating as though they constituted a triode in which the emitter 3a and the collector 4 represent the cathode (since they are effectively connected together by thecondenser K). The electrode 3 represents the grid and the electrode do the anode.

The stabilizing valve VI is operated exactly as in Fig. 3, but is in this case connected across resistance R4, and thereby regulates the difference of potential of the electrode pairs 3, 3a and 4a. In this circuit also the grid 2 is maintained at a constant potential through the leak re sistance G.

When it is desired to use this circuit for very high frequencies, the inductances L2 and L3 may be replaced by transmission lines of suitable design and electrical length. arranged to have the desired positive reactances' for the frequency concerned.

Fig. 5a gives a sketch of such a transmission line shown as a concentric cable, though it need not be of this form. When two lines similar to Fig. 5a are used instead of L2 and L3, the terminals :01 and $2 of one line will be connected to terminals 2i and 22, respectively, in 5, and the terminals $1 and m2 of the other to 23 and 25. The output terminals of both lines may be shortcircuited, as shown, the lengths being chosen accordingly.

In Fig. 6 is shown a somewhat different arrangement, analogous to the so-called dynatron circuit. The electrodes 3 and 3a are separated and the tuned circuit L4, C3 is connected in series with da. Since there is secondary emission from 3a, a negative resistance is obtained across the tuned circuit, which, by suitable adjustment, can be arranged to cancel out the positive resistance therein. Control of the negative resistance is obtained by the use of the valve Vl connected between the plate 3 and the cathode i, which, as in Fig. 3, is operated from the transformer T in exactly the same way. As before, the grid 2 is maintained at a constant potential through the leak resistance G. If the secondary emission produced by the electrode 3a is insufficient to produce the desired negative resistance, connection may be made instead to one of the other secondary emitters, for example, to 4a. Alternatively, control of the negative resistance may also be obtained by using a variable bias on the control grid 2 which can be produced in a number of known ways. The impedance Z is as before used to adjust the relative phases of the electrodes 3 and to. By making use in this way of the negative resistance property of the secondary emitter, the diiiiculties associated with phase shift are substantially reduced.

In all the circuits just described, the method of supplying the required potentials to the electrodes shown in Fig. 1 has been used, but any other convenient method could also be adopted, without making any essential change in the principles involved.

One of the difiiculties associated with generating extremely high frequency oscillations is that the interelectrode capacities of the associated valve are liable to be the controlling factors which set an upper limit to the frequencies which can be obtained.

In ordinary valves it becomes difficult to reduce these capacities, for instance by reducing the dimensions of the electrodes and their connecting leads, because owing to their rather close 8 proximity to the cathode they are liable to be overheated. It is possible to overcome these difficulties by means of a modification to the multiplying valve shown in Fig. 1, because the electrodes which are used for generating the oscillations are not the same as the electrodes involved in the original production of the electron stream.

In Fig. 8 is shown a multiplying valve modified in accordance with one of the features of the invention. It will be seen that the multiplying electrodes have been spaced from the electrodes generating the electrons, whereby they are prevented from becoming appreciably heated by radiation from the cathode. The electrodes in Fig. 8 are denoted by the same numbers as the corresponding electrodes in Fig. 1, and certain extra electrodes have been introduced. Thus, the electron stream is produced by the electrodes I, 2 and 3, as before, and the electrons travel some distance before they meet the first emitter electrode lla. An extra collector II has been inserted in front of I la, and owing to the distance which the electrons have to travel before reachin the other electrodes, a focussing device consisting, for example, of a tubular electrode H) has been shown inserted behind the electrode 3 in order to concentrate the electron beam so that it shall strike the emitter electrode Ha. The circuit whereby the Fig. 8 modification generates oscillations, is connected in the same manner as the Fig. 3 circuit, the electrode Ha being similar in function to electrode 3a in Fig. 3. The operation of the Fig. 8 circuit in producing oscillations will thus be clear from the description of the Fig. 3 circuit.

It is not necessary that the oscillations should contain any appreciable power when they are actually generated, since they are amplified in the valve by the succeeding multiplying stages. Accordingly, the first gew pairs of electrodes may be of very small dimensions so as to introduce only very small capacaties. The succeeding electrodes, however, must be of larger dimensions in order to enable them to handle the power as it increases in the succeeding stages. This progressive increase in the dimensions of the electrodes is indicated in Fig. 8.

The first three pairs of electrodes have been shown separated, but connected externally through impedances ZI, Z2 and Z3. These are simply to indicate diagrammatically that these electrodes may be connected in some way to an oscillating circuit. The extra electrode II has been inserted in order that all the secondary electrons produced by Ila may be reflected and directed forwards, and also for the purpose of supplying the electrode corresponding to the plate which is now no longer available for use in connection with the associated oscillating circuit. The modified valve as shown in Fig. 8 may be supplied with the appropriate potentials from a potentiometer circuit like that in Fig. l, and an extra tapping on resistance R3 is shown dividing it into two parts R3A and B3B, in order to provide the focussing electrode 10 with a potential higher than that of the plate 3. As already menticned, however, it is not essential that the valve should be supplied in this way; and also it could have, if desired, more pairs of multiplying electrodes, and other kinds of focussing arrangements could be used.

By means of this modified multiplying valve,

therefore, it has become possible to reduce the dimensions of the electrodes associated'with the oscillating circuit, so that their controlling effect on the external circuits will be greatly reduced, and, moreover, since the load is in fact connected to the oscillating circuit through an amplifying arrangement, there will be substantially no reaction upon the frequency of the oscillation. It will thus be seen that the invention provides a means for generating exceedingly high frequencies which may be automatically controlled and may also be amplified to any desired degree with the equivalent of only one valve.

Of the arrangements which have been shown and described, that of Fig. (particularly when transmission lines as shown in Fig. 5a are used for the inductances L2 and L3) is preferable for very high frequencies, for example 300 megacycles or more. In order to make best use of this circuit, the multiplying valve M should be of the type shown in Fig. 8 in order that the capacities associated with the oscillating electrodes may be made small enough to prevent the frequency from being limited thereby. When lower frequencies are required, (for example, frequencies of, the order of 30 megacyoles), Fig. 3 or 6 may be satisfactorily used, with or without using a multi plying valve according to Fig. 8. If the multiplying valve available is of the known type shown in Fig. 1, then the oscillating circuit may be as shown in Fig. 4.

The invention is not limited to the embodiments which have been described for the purpose of illustration, and various modifications of the arrangements shown which are within the scope of the invention will occur to those skilled in the art.

What is claimed is:

1.. An ultra high frequency oscillation generator comprising an electron multiplier valve including a plurality of secondary emission multiplying electrodes arranged in series between the anode and cathode thereof and a control grid adjacent said cathode; and an oscillating circuit connected with the control grid and a secondary emission electrode, said circuit including a resistance between said grid and the latter electrode.

2. An osc llation generator as set forth in claim 1, in which the value of said resistance is selected to maintain said grid substantially at the minimum oscillating potential and which includes an output stabiliz ng means including means for varying said grid potential.

3. An ultra high frequency oscillation generator comprising an electron multiplier valve including a plurality of secondary emission multiplying electrodes in series between the anode and the cathode thereof. a plurality of collector electrodes each associated with a multiplying electrode and located on the cathode side thereof, and a control grid; impedance means connected between a multiplying electrode and the associated collector electrode for maintaining the same potential phase on the multiplying electrode as on said control grid, and an oscillating circuit connected to electrodes of said valve. 7

4. An oscillation generator as set forth in claim 3, in which the oscillating circuit includes a feedback resistance connected between a multiplying electrode and the control grid, and output stabilizing means including means connected between the latter multiplying electrode and the control grid-cathode circuit for varying the control grid potential in accordance with variations in thevalve output.

5. An ultra high frequency oscillation generator comprising a multiplier valve including a plurality of multiplying electrodes in series between the anode and the cathode thereof a control electrode adjacent said cathode, spacing between the cathode and the next one of the multiplying electrodes being substantially wider than the'succeeding inter-electrode spacing, the arrangement being such that said electrodes receive a substantially reduced proportion of cathode heat; and an oscillating circuit connected to said control electrode.

6. An ultra high frequency oscillation generator comprising a multiplier valve including a plurality of multiplying electrodes in series between the anode and the cathode thereof, the multiplying electrodes adjacent to the cathode being substantially smaller than the succeeding multiplying electrodes; and an oscillating circuit connected to said smaller electrodes.

7. An oscillation generator as set forth in claim 6, in which the dimensions of the multiplying electrodesprogressively increase with their distance from the cathode.

8. An ultra high frequency oscillation generator comprising a multiplier valve including a plurality of multiplying electrodes and a control electrode arranged in series across a substantially straight electron path extending from the cathode to the anode of said valve, and a feedback circuit connected between one of said electrodes and the control electrode.

-9. An ultra high frequency oscillation generator comprising a multiplier valve including a plurality of multiplying electrodes and a control electrode arranged in series across a substantially straight electron path extending from the oathode to the anode of said valve, and an oscillating circuit connected between one of said electrodes and the control electrode.

10. An ultra high frequency oscillator generator comprising a multiplier valve including a plurality of multiplying electrodes and a control electrode arranged in series across a substantially straight electron path extending from the cathode to the anode of said valve, and an oscillating circuit connected between one of said electrodes and the control electrode, the near one of the multiplying electrodes being substantially wider than the succeeding inter-electrode spacing, the arrangement being such that said electrodes receive a substantially reduced proportion of cathode heat.

11. An ultra high frequency generator comprising an electron-multiplying valve including a plurality of secondary emission-multiplying electrodes, and a control grid in series arrangement between the anode and the cathode thereof, and an oscillating circuit for controlling the frequency of the oscillations generated connected between a first one of the series of multiplying electrodes and the control grid, the connection of said circuit including a resistance.

12. An ultra high frequency generator comprising an electron-multiplying valve including a series of electrodes from cathode through grid to a final one of a series of electron-multiplying electrodes, connections including an oscillatory circuit between the grid and a multiplying electrode relatively near to the cathode for producing oscillations, the spacing between grid and said relatively near multiplying electrode being larger than that between succeeding multiplying electrodes, said succeeding electrodes having spacings decreasing with the distance from the grid and sizes increasing with the decreasing spacings.

13. In a generator according to claim 9, a mull i tiplying electrode relatively near the cathode and a succeeding one each comprising a collecting member and a secondarily emissive member insulated from one another, oscillating circuits connecting said'members to the control electrode and a capacity coupling between the collecting member of the near electrode and the emissive member of the succeeding one.

14. In a generator according to claim 9, a multiplying electrode relatively near the cathode and a succeeding one each comprising a collecting member and a secondarily emissive member insulated from one another, oscillating circuits connecting said members to the control electrode and a capacity coupling having substantially no impedance between the collecting member of the near electrode and the emissive member of the succeeding one, said oscillatory circuits being substantially inductive and forming coaxial transmission lines.

ROY MAYNE BARNARD. ALBERT COOPER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,732,050 Jobst Oct. 15, 1929 2,073,599 Malter Mar. 9, 1937 10 2,130,272 Ford Sept. 13, 1938 2,182,870 Jarvis Dec. 12, 1939 2,220,452 Jarvis Mar. 5, 1940 2,055,090 Rust Sept. 22, 1936 2,181,720 Barthelemy Nov. 28, 1939 15 2,190,069 Hollmann Feb. 13, 1940 2,205,071 Skellett June 18, 1940 2,235,497 Heil Mar. 18, 1941 2,257,942 Farnsworth Oct. 7, 1941 0 FOREIGN PATENTS Number Country Date 502,472 British Mar. 17, 1939 540,893 British V Nov. 4, 1941

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