US2263825A - Signal translating stage - Google Patents

Description

Nov. 25, 1941 A. I. LOUGHREN 2,263,825

SIGNAL TRANSLATING STAGE Filed May 15, 1940 2 Sheets-Sheet 2 FIG.6.

Grid Voltage Grid Volta'ge i INVENTOR ARTHUR V. LOUGHREN ATTORNEY Patented Nov. 25, 1941 UHTED SIGNAL TRANSLATING STAGE Arthur V. Loughren, Great Neck, N. Y., assignor to Hazeltine Corporatio ware n, a. corporation or Dela- Application May 15, 1940, Serial No. 335,238

(Cl. 250-20) l 1'7 Claims.

This invention relates generally to signaltranslating stages for the translation of signals within a wide amplitude range and particularly to such stages in which the gain is controlled inversely in accordance with the amplitude of the signal input to the stage.

Under normal operating conditions, a modulated-carrier signal receiver is utilized for the reception of signals of amplitudes varying within very wide limits. As a result, the signal input to the first repeater stage of the receiver normally has a correspondingly wide range of amplitude variations. For weak signals, it is desirable to maintain the transmission characteristics or the response of the preselector between the antenna and the first repeater stage of the receiver at a maximum in order to raise the received signals substantially above the noise level,

thus to procure maximum useful sensitivity of the receiver. However, with a high gain in the preselector, as the strength of desired received signals increases to such an extent that the grid swing of the first repeater stage includes a substantial nonlinear portion of the characteristic curve of the repeater, distortion of the desired signal-modulation envelope and cross modulation of the desired signal-carrier wave by strong undesired signals may result. This is particularly true in the case of receivers provided with automatic amplification control by which strong signals cause the grid of the first repeater stage to be biased toward that portion of its characteristic which is most nonlinear. The undesired signals, as well as desired signals, which reach the grid of the first repeater stage 01 the receiver have the .efiect of causing the grid to swing over such a range that these disturbing effects result. It is well known that such envelope distortion and cross modulation are efiects which cannot be filtered out by succeeding selective circuits of the receiver.

In general, the preselector of a receiver, that is, the selector circuit between the antenna and the input circuit of the first vacuum-tube remore, this does not remove the envelope distortion of abnormally strong desired signals.

Various expedients have heretofore been proposed for automatically and adjustably attenuating the input to the first repeater stage or a modulated-carrier receiver in order to eliminate the disturbing effects described above. In certain of these arrangements, adjustable impedance elements such as vacuum tubes have been connected in circuit with'the preselector circuit oi the receiver adjustably to damp such circuit, thereby adjustably to attenuate the signal input to the first repeater stage. Other proposed arrangements for this purpose comprise two feed-forward coupling paths between the antenna and the first vacuum-tube repeater of the signal-translating channel so arranged as to apply signal voltages of opposite phase to the input circuit of the first repeater, the transmission characteristics of one of the coupling paths being adjustable. While such arrangements provide generally satisfactory operation, they have generally required the use of one or more additional vacuum tubes or other circuit complexities that tended to increase the cost oi. the receiver.

It is an object 01' the invention, therefore, effectively to provide an improved, simple, and economical signal-translating stage which may .be easily adjusted to control the sensitivity or a modulated-carrier signal receiver in such manner as to eliminate the undesired effects described above.

It' is another object of the invention effectively to provide a signal-translating stage which secures the desired characteristics described without affecting the selectivity of a radio-frequency selector with which it is associated.

It is still another object of the invention to provide a signal-translating stage: adapted for 40 the translation or a signal input which varies tion eilects.

pea-ter in the signal-translating channel, should be selective to pass a band of desired modulation frequencies sufiiciently wide to provide the desired fidelity of reproduction. Generally speaking, if an attempt is made to decrease the total desired and undesired signal input of the first repeater stage by discriminating against the un- In accordance with the invention, a signaltranslating stage comprises a vacuum tube including a source of electrons, an anode, a control electrode, and a signal-input electrode between said control electrode and said anode etdesired signals passed by the selector by adjusting its band width, the fidelity of reproduction fective to control the electron stream from the source to the anode and having a greater effect on the electron stream over one cross-sectional portion of the electron path than on that over is impaired to an undesirable degree. Furtheranother portion so that, normally, the transconductance from the control electrode to the anode is primarily determined by the control of ace-spas derived. The audio-frequency signals are, in turn, amplified by the audio-frequency amplifier i8 and supplied to sound reproducer I! for reproduction. The automatic amplification control bias derived from unit I! is effective to maintain the signal input to detector 15 within relatively narrow limits for a wide range of received signal intensities.

Referring now-more particularly to the signaltranslating stage i2 of the invention, this stage comprises a vacuum tube including, in the order named, a source of electrons such as a cathode ii, a first or control electrode 22, a second electrode 22, a third or signal-input electrode 24, a screen electrode 25, and an anode 26. The

' signal-input electrode 24 is effective primarily to For a better understanding of the invention, together with other and further objects thereof,

reference is had to the following description taken in connection with the accompanying drawingaand its scope will be pointed out in the appended claims.

Referring now to the drawings, Fig. 1 is a ditcuit diagram, partly schematic, of a modulatedcarrier signal receiver of the superheterodyne type including a signal-translatingstage in accordance with the invention; Figs. 2' and 3 are circuit diagrams of modifications of the signal-- translating stage of Fig. 1; Fig. i ls a circuit diagram. partly schematic, of a receiver of the su-' perheterodyne type including a signal-translatcontrol the variations in electron stream from cathode 2i to anode 26 at signal-input frequen cies and is so designed as effectively to extend ing stage in'accordance with the invention and Figs. 6 and 'l comprise graphs utilized to explain the operation of the circuit of Fig. 1.

Referring now particularly to Fig. 1 of the drawings, there is shown a circuit diagram, partly schematic, of a complete modulated-carrier signal receiver of the superheterodyne type employing the invention. This receiver comprises, coupled in cascade with an antenna-ground circuit I0, I I, a radio-frequency amplifier I2, a frequency changer or oscillator-modulator i3, an intermediate-frequency amplifier i4 of one or more stages, a detector and automatic amplification control or A. V. C. supply IS, an audio-frequency amplifier it of one or more stages, and a sound reproducer .11. Automatic amplification control is secured in a well-known manner by applying a unidirectional voltage derived from the A. V. C. supply 15 to the control electrodes of oscillatormodulator i3 and one or more of the tubes included in the intermediate-frequency amplifier l4. Automatic amplificationcontrol potentials are also applied to radio-frequency amplifier If in a manner to be hereinafter fully described.

Neglecting for the present the details of operation of signal-translating stage i2. of the present invention, the apparatus described constitutes, in general, a conventional superheterodyne wave-signal receiver, the operation of which is well-understood in the art. In brief, signals intercepted by antenna-ground circuit l0, II are translated to the input circuit of radio-frequency amplifier l2, are amplified therein and translated to oscillator-modulator i3 wherein they are converted to an intermediate-frequency signal. The intermediate-frequency signal is amplified in intermediate-frequency amplifier I4 and delivered to detector I! wherein the audio-frequency signals and the A. V. ,C. biasing potentials are 75 the path directly through grid 24 is mainly etover only a portion of the cross-sectional area oi the electron path from cathode 2i to anode 24. An additional'or auxiliary electrode 21 is pro vided which extends over another portion of the cross-sectional area of the electron path between cathode 2i and anode 2| and is generally complementary to the signal-input electrode 24. Electrode 24 is loosely coupled to electrode 21 by means of capacitance 8i shown in dotted lines for the reason that it may be comprised in whole or inpart or the interelectrode capacitance be-- tween these electrodes. Electrode 21 is also designed so as to extend over only a portion of the entire cross-sectional area of the electron path. Positive operating potentials are supplied to electrodes 23 and 25 and anode 26 from suitable sources, while negative operating potentials are supplied to electrodes 24 and 21, the operating potential applied to electrode 21 being applied through an impedance 21'. A negative voltage, variable in accordance with the amplitude of received signals, is applied to electrode 22 from the A. V. C. supply source ll.

in considering the operation of the signaltranslating stage of Fig. 1, it will be seen that signal-input electrode 24 has more effect on one portion, which may be called portion A, of the cross-sectional area of th cathode-anode electron path than on another portion, that is, the portion over which electrode 21 extends, which may be called portion B, so that, normally, that is, in the absence of an appreciable negative potential applied to electrode 22 from the A. V. C.

fect the transconductance between electrode 24 and anode 28, but only to a relatively small degree, due to the action of electrode 21 on the portion B of the electron stream.

As the negative bias applied to electrode 22 is increased, due to an increased signal-input amplitude and an increased A. V. C. bias, the ratio of the density of the electron stream over portion B to that over portion A is increased, whereby the portion of the transconductance between sig- A. V. C. voltage applied to control electrode 22,

fective in determining the transconductance between signal-input electrode 24 and anode 26. As a larger A. V. C. bias is applied to electrode 22, the transconductance of this path may be gradually decreased to complete cutoff and the resultant transconductance from signal-input electrode 24 to anode is then only that due to the electron stream through grid 21. The means for applying the unidirectional A. V. C. control potential to control electrode 22 is thus efiective to increase the average density of the electron stream over portion B relative to that over portion A, whereby the portion of the transconductance of the tube determined by the electron stream through portion B is materially increased. Also, it is preferable that the electrode structure of the tube is so related to its operating poten* tials that screen electrode 23, to which a positive potential is applied,.is efiective, together with the the electron current to anode 26 may be controlled by the signal voltages on electrodes 24 and 21.

Reference is made to the graphs of Figs. 8 and connected to cathode 2|. A resonant circuit 23,

84 is included in the anode circuit of tube 30. and it will be understood that the remainder of tron stream by virtue of its electrostatic field which extends somewhat over the remainingpom tion of the electron path. Suppressor electrode 32 has the same purpose in the tube as the suppressor electrodes of conventional tubes,

which purpose iswell understood by those skilled in the art.

In Fig. 3, there is shown a signal-translating stage generally similar to that ofFig. 2 and circuit elements which are similar to those of Figs.

1 and 2 have identical reference numerals. The

1 signal-translating stage of Fig. 3 comprises a 7 for a further explanation of the operating characteristics of the signal-translating stage II.

The curve A of Fig. 6 represents the grid voltage-anode current characteristic of portion A of tube 20, while curve B represents the corresponding characteristic for portion B. If an input signalof small amplitude is applied to control electrode 24 or tube '20.'the resultant grid voltage-anode current characteristic of the tube is that represented by the sum of curves A and B,

which is represented by curve C. Thus, for a small signal input, as indicated by curve a, a relatively large signal output. as indicated by the curve a, is obtained. Similarly, if the input signal is very large, as indicated by the c e b, the effective or over-all input voltage-outpu current characteristic of the tube is that of curve B and an output signal represented by the curve b is obtained from the stage. If now an input signal of intermediate amplitude value is applied to the signal-translating stage, it is seen that an A. V. C. bias is developed and applied to electrode 22 eflectively changing the transconductance characteristic of portion A of the tube and the changed characteristic may be as represented by curve A of Fig. 7. The characteristic of portion B is not materially changed, so that the over-all characteristic of the tube is that represented by the sum of curve A of Fig. 7 and curve B of Fig. 6, which over-all characteristic is illustrated by the curve D. Therefore, for an input erally similar to the signal-translating stage i 2 of Fig. 1 and similar circuit elements have identical reference numerals. The tube 30 of Fig. 2 is generally similar to the tube of Fig.1 except that electrode 21 has been omitted and there is included a suppressor electrode 32 disposed between screen grid 25 and anode 26 and 43, by-passed for signal-frequency currents by condenser 44, is provided for tube 40, electrode 4| being grounded.

In considering the operation of the signaltranslating stage of Fig. 3 it will be.seen that,

for received signal amplitudes of. low value, for which maximum gain is required from tube 40,"

substantially .no current flows through grid 21 due to the effect of negatively biased electrode 4| and the electron stream through the signalinput grid 24 is mainly effective to determine transconductance between control electrode 24 and anode 28.r As the amplitude of received signals increases, the bias applied to electrode 22 from the A. V. C. source gradually increases. ultimately cutting oil the electron stream through control electrode 24. and reducing the negative bias on grid 4| so that an electron path is open through grid 4| to anode 28. That is, sufiicient bias voltage is developed-across resistor 43 to cut oil the electron stream through grid 4| when a small A. V. C. 'bias is applied to grid 22 and, as the A. ,V. C. bias to grid 22 increases, the bias voltage developed in resistor 43 for grid 4i is decreased, thereby permitting the electron stream to flow through grid 4| and grid 21 in a path which is controlled to 'a much lesser'extent by the potential of signal-input electrode 24. '.It

is, therefore, seen that the transc'onductance of portion B of the tube of Fig. 3 increases from a negligible value to some value as represented by the curve B of Fig. 6 while the transconductance of portion A of the tubes falls-from avalue as represented by curve A of Fig. 6 to acre.

. The signal receiver represented in Fig. 4 is generally similar to that of Fig. 1 and similar circuit elements have identical reference numerals. Thecircuit of Fig. 4 diflers from that of Fig. l primarily in that it contains no stage of radio-frequency amplification, the signal-translatmg stage of the invention being included in the circuit of the receiver as a converter stage ior developing an intermediate-frequency signal for intermediate-frequency. amplifier l4. signal-translating stage of Fig. 4 includes a vacuum tube 50 having between screen electrode 21 and anode 26 an electrode supplied with oscillations from a conventional local oscillator 53. It is believed that the operation of the circuit of Fig. 4 will be readily apparent from the description of the circuits of the preceding figures; that is, the action oi. grid 24 is generally similar and the oscillation voltage supplied to grid 5| is also efiective to vary or modulate at the frequency of local oscillator 53, the resultant electron stream to anode 26. Therefore, for a received signal of low amplitude, the conversion transconductance from signal-input electrode 24 aaoaaas electron stream over said other of said portions to that over said one or said portions, whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

2. A signal-translating stage comprising, a vacuum tube including a source of electrons, an anode, a control electrode, and a signal-input electrode between said control electrode and said anode eflective to control the electron stream from said source to said anode and extending over only a portion 0! the cross-sectional area of the electron path whereby it has a greater eflect on the electron stream over said portion than on that over another portion so thatnormally the transconductance from said signalto anode 26 is primarily determined by the electron stream through the grid-24. For strong signals, however, the conversion transconductance from signal-input electrode 24 to anode 28 is primarily determined by the electron stream through grid 21, the potential applied to signalinput electrode 24 having a lesser effect upon this portion of the electron stream.

The receiver of Fig. 5 is generally similar to that of Fig. 4 and similar circuit elements have identical reference numerals. The receiver of Fig. 5 differs from that of Fig. 4 in that the signal-translating stage embodying the invention is an oscillator-modulator, there being included in such signal-translating stage means for developing sustained oscillations which are applied source of operating potential +B, there is shown included in intermediate-frequency amplifier ll an anode load impedance for intermediate ire- 'quencies which comprises tuned circuit 33, 3| to which is inductively coupled an inductanc 51. It will be understood that the remaining portions oi. intermediate-frequency amplifier H which are not shown may be of conventional construction and operation.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A signal-translating stage comprising, a vacuum tube including a source of electrons, an' anode, a control electrode, and a signal-input electrode between said control electrode and said anode efiective to control the electron stream from said source to said anode and having a greater efiect on the electron stream over one cross-sectional portion of the electron path than on that over another portion so that normally the transconductance from said signal-input electrode to said anode is primarily determined by the control of the electron stream through said one portion, and means for applying a unidirectional potential to said control electrode for increasing the ratio of the average density 01' the input electrode to said anode is primarily determined by the control or the electron stream through said one portion, and means for applying a unidirectional potential to said control electrode for increasing the ratio of the average density of the electron stream over said other of said portions to that over said one of said portions. where-' by the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

3. A signal-translating stage comprising, a

vacuum tube including a source of electrons, an anode, a control electrode, a signal-input electrode between said control electrode and said anode efiective to control the electron stream from said source to said anode and effectively extending over only a portion of the cross-sectional area oi. the electron path, whereby it has a greater effect on the electron stream over one cross-sectional portion of the electron path than on that over another portion, an auxiliary signalinput electrode effective to control the electron stream from said source to said anode extending over said other portion and normally being less effective than said signal-input electrode so that normally the transconductance from said signalinput electrode to said anode is primarily determinedby the control of the electron stream through said one portion, and means for applying a-unidirectional potential to said control electrode for increasing the ratio of the average density oi. the electron stream over said other of said portions to that over said one of said portions, whereby the portion of said transconductance determined by the stream through said other of said portions is materially increased.

4. A signal-translating stage comprising, a vacuum tube including a source of electrons, an anode, a signal-input electrode eil'ective to control the electron stream from said source to said anode efi'ectively extending over only a portion of the cross-sectional area of the electron path. whereby it has a greater eflect on the electron stream over one cross-sectional portion of the, electron path than on that over another portion, an auxiliary control electrode effective to control the electron stream from said source to said anode extending over said other portion so that normally the transconductance from said signalinput electrode to said anode is primarily determined by the control of the electron stream through said one portion, means for applying a signal input to said signal-input electrode and for applying a small fraction of said signal input to said auxiliary electrode, and means for increasing the ratio of the average density of the electron stream over said other of said portions by the stream through said other of said portions is materially increased.

5. A signal-translating stage comprising, a vacuum tube including a source of electrons,'an anode, a control electrode, a signal-input electrode between said control electrode and said anode effective to control the electron stream from said source to said anode and having a greater effect on the electron stream over one cross-sectional portion of the electron path than on that over another portion, and an auxiliary control electrode effective to control the electron stream from said source to said anode and having a greater effect on said other portion than on said one portion, said stage including means loosely coupling said signal-input electrode and said additional control electrode so that normally the, transconductance between said signal-input electrode and said anode is primarily determined by the control of the electron stream through said one portion, and means for applying a unidirectional potential to said control electrode for increasing the ratio of the average density of the electron stream over said other of said portions to that over said one of said portions, whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

6. A signal-translating stage comprising, a vacuum tube including a source of electrons, an anode, a control electrode, a signal-input electrode between said control electrode and said anode efiective to control the electron stream from said source to said anode and having a greater efiect on the electron stream over one cross-sectional portion of the electron path than on that over another'portion, and an auxiliary control electrode efiective to control the electron stream from said source tov said anode and having a greater effect on the electron stream over said other portion than on that over said one vacuum tube including a source of electrons, an anode, a control electrode, and a signal-input electrode between said control electrode and said anode eifective to control the electron stream from said source to said anode and having a greater effect on the electron stream over one cross-sectional portion of'the electron path than on that over another portion so that normally the transconductance from said signal-input electrode to said anode is primarily determined by the control of the electron stream through said one portion, and means for applying a variable negative potential to said control electrode for increasing the ratio of the average density of the electron stream over said other of said portions to that over said one of said portions,

whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

9. In a modulated-carrier signal receiver including an antenna and a signal-translating channel, a first signal-translating stage in said portion, said stage including means incidentally coupling said signal-input electrode and said auxiliary electrode and including the interelectrode capacitance between said electrodes so that normally the transconductance from said signalinput electrode to said anode is primarily determined by the control of the electron stream through said one portion, and means for applying a unidirectional potential to said control electrode for increasing the ratio of the average density of the electron stream over said other of said portions tothat over said one of said portions. whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

'7. A signal-translating stage comprising, a vacuum tube including means for forming a virtual cathode, an anode, and a signal-input electrode efiective to control the electron stream from said virtual cathode to said anode and having a greater efiect on the electron stream over one cross-sectional portion of the electron path than on that over another portion so that normally the transconductance from said signalinput electrode to said anode is primarily determined by the control of the electron stream through said one portion, and means for increasing the ratio of the average density of the electron stream over saidother .of said portions to that over said one of said portions, whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

8. A signal-translating stage comprising, a

signal-translating channel comprising, a vacuum tube including a source of electrons, an anode, a control electrode, and a signal-input electrode between said control electrode and said anode effective to control the electron stream from said source to said anode and having a greater efiecton the electron stream over one cross-sectional portion of the electron path than on that over another portion so that the transconductancefrom said signal-input electrode to said anode is'primarily determined by the control of the electron stream through said one por'tion,'means for coupling said signal-input electrode to said antenna, and means for applying a unidirectional potential to said control electrode for increasing the ratio of the average density of the electron stream over said other or said' portions to that over said one of said portions, whereby the portion of said transconductance determined by the electron stream through said other of tions is materially increased.

10. In a modulated-carrier wave-signal receiver including an antenna, a signal-translating channel, and a source of automatic amplification control voltage, a first signal-translating stage in said signal-translating channel comprising, a vacuum tube including a source of electrons, an anode, a control electrode, and a signal-input electrode between said control electrode and said anode effective to control the electron stream from said source to said anode and having a greater effect on the electron stream over one cross-sectional portion of the electron path than on that over another portion so that normally the transconductance from said signal-input electrode to said anode is primarily determined by the control of the electron stream through said one portion, means for coupling said signal-input electrode to said antenna, and means for applying a potential from said source of automatic amplification control voltage to said control electrode for increasing the ratio of the average density of the electron stream over said other of said portions to that over said one of said portions, whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased for received signal amplitudes of large value,

11. A signal-translating stage comprising, a vacuum tube including, in the order named. a

said porcathode, a first electrode, a secondelectrode, a

signal-input electrode, and an anode. means for applying a positive unidirectional operating potential to said second electrode, said signal-input electrode being eflective to control the electron stream from said source to said anode and having a greater efiect on the electron stream over one cross-sectional portion of the electron path than on that over another portion so that normally the transconductance from said signalinput electrode to said anode is primarily determined by the control of the electron stream through said one portion, and means for applying a variable negative potential to said first electrode for increasing the ratio of the average density of the electron stream over said other of said portions to that over said one of said portions, whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

12. A signal-translating stage comprising, a

0! the average density of the electron stream over said other of said portions to that over said one of said portions, whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

15. A signal-translating stage comprising, a

control electrode including, in the order named,

a source of electrons, a signal-input electrode, a 1

screen grid, an additional electrode, and an anode, said signal-input electrode being effective to control the electron stream from said source to said anode and having a greater eifect on the electron stream over one cross-sectional portion of the electron path than on that over another portion, means comprising said additional elecvacuum tube including a source of electrons, an

trode for varying the electron stream to said anode at a preselected frequency, whereby the normal conversion ttansconductance from said signal-input electrode to said anode is primarily determinedby the control of the electron stream through said one portion, and means for increasing the ratio of the average density of the directional potential to said control electrode for decreasing the density of the electron stream over said one portion, whereby the portion of said transconductance determined by the electron stream passing through said other oi said portions is materially increased.

13. A signal-translating stage adapted to translate signal inputs within a wide amplitude range comprising, a vacuum tube including a source of electrons, an anode, a control electrode, and a signal-input electrode between said control electrode and said anode eiiective to control the electron stream from said source to said anode and having a greater efiect on the electron stream over one cross-sectional'portion oi the electron path than on that over another portion so that normally the transconductance from said signal-input electrode to said anode is primarily determined by the control of the electron stream through said one portion, and means responsive to the amplitude of said signal input for applying a unidirectional potential to said control electrode for increasing the ratio of the average density of the electron stream over said other of said portions to that over said one of said portions. whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

14. A signal-translating stage comprising, a vacuum tube including a source of electrons, an anode, a signal-input electrode efiective to control the electron stream from said source to said anode and having a greater efiect on the electron stream over one cross-sectional portion of the electron path than on that over another portion so that normally the conversion transconduct- .ance from said signal-input electrode to said anode is primarily determined by control of the electron stream through said one portion, an additional means for varying at a preselected frequency the electron stream from said source to said anode, and means for increasing the ratio electron stream over said other of said portions to that over said one of said portions, whereby the portion of said transconductance determined by the electron stream through said other of said portionsis materially increased.

16. A signal-translating stage comprising, a vacuum tube including a source of electrons, an anode, and a signal-input electrode efiectiveto control the electron stream from said source to said anode and having a greater eiiect on the electron stream over one cross-sectional portion of the electron path than on that over another portion so that normally the conversion transconductance iromsaid signal-input electrode to said anode is primarily determined by the control of the electron stream through said one portion, means included in said vacuum tube for providing sustained oscillations and for utilizing said oscillations to vary the electron stream to said anode, and means for increasing the ratio of the average density of the electron stream over said other of said portions to that over said oneoi said portions, whereby the portion of said transconductance determined by the electron stream through said other of said portions is materially increased.

17. A signal-translating stage comprising, a vacuum tube including, in the order named, a source of electrons, a signal-input electrode, a screen electrode, an additional electrode, and an anode, means including said additional electrode for providing sustained oscillations and for utilizing said oscillations to control the electron stream to said anode, said signal-input electrode being effective to control the electron stream-from said source to said anode and having a greater effect on the electron stream over one cross-sectional portion of the electron path than on that over another portion so that normally the conversion transconductance from said signal-input electrode to said anode is primarily determined by the control of the electron stream through said one portion, and means for increasing the ratio of the average density of the electron stream over said other of said portions to that over said one of said portions, whereby the portion of said transconductance determined by the electron ARTHUR V. LOUGHREN.

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