US2118845A

US2118845A - Amplifier

Info

Publication number: US2118845A
Application number: US686338A
Authority: US
Inventors: Clarence W Hansell
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1933-08-23
Filing date: 1933-08-23
Publication date: 1938-05-31
Anticipated expiration: 1955-05-31
Also published as: DE661909C

Description

5 Sheets-Sheet 1 AMPLIFIER c. w. HANSELL Filed Aug. 25, 1953 any 31, 1938.

AA/ODE POM fl? .SIIPPZ Y 500/965 INVENTOR CZAAE/VCE Wf/AA/SELL ATTORNEY ay 31, 1938. c. W. HANSELL 2,111,845

AMPLIFIER Filed Aug. 23, 1933 3 Sheets-Sheet 2 NQQER TU INVEVNTOR LARENCE WJ/A/l/JZ'LL ATTORNEY C. W. HANSELL AMPLIFIER Filed Aug. 23, 1933 3 Sheets-Sheet 3 INVENTOR L a J M H. w a m R M C n N m n A l'i'E This invention relates STATES AMPLIFIER Clarence W. Hansell, Port Jefierson, Y, as-

signor to Radio Corporation poration of Delaware Application August 23,

18 Claims.

to electron discharge device circuits, and particularly to such of these circuits as may be used for the amplification of signals.

An object of the present invention is to enable the amplification of extremely wide bands of frequencies with simplicity and high efiiciency.

A further object is to provide an arrangement wherein there may be utilized vacuum tubes which function with high positive D. C. potentials on the control elements, but with little or no current fiow to these control elements.

These and other objects are achieved, in accordance with the present invention, by the provision of an axial magnetic field around an electron discharge device whose output and input electrodes are supplied preferably with approximately equal positive potentials.

In one form of vacuum tube, which forms part of my invention, the magnetic field is arranged to have sufi'icient strength to reduce the anode current to zero while at the same time it permits considerable current to flow to the grid. Under such conditions, if the anode potential is varied the amount of grid current can also be varied without causing any flow of current to the anode which in this case may act as the control element.

Since only a relatively small amount of anode power is needed for this purpose the tube is thus available for power amplification.

One advantage of the present invention is that a magnetron may be used for the electron discharge device, or even an ordinary three element tube which is supplied with an axial field.

Another advantage is that a system utilizing such electron discharge devices in accordance with the present invention in a chain of amplifiers avoids the necessity for employing blocking condensers or coupling circuits between the anode of one tube and the control electrode of the next succeeding tube obtained a simplification consequently there is of the circuit and an increase in maximum operating frequency without any difficulties due to capacity to ground, etc., of the blocking condensers or coupling circuits.

Referring to the drawings, Figure 1 shows a magnetron vacuum tube of a type which may anode magnetron tubes.

Figure 4 illustrates,

of America, a cor- 1933, Serial No. 686,338 (01. 179-171) in simplified form, the application of my invention to push-pull circuits and to circuits in which undesired capacitive feed-back from output to input circuits is neutralized.

In Figure 1 there is illustrated in cross section 5 a magnetron comprising an electron discharge device having an evacuated envelope l0 containing within it at its center an electron emitting cathode II surrounded by an anode I2 and a grid-like structure l3. It is proposed to provide 10 this grid structure with rather widely spaced radial and vane-like elements on a circle almost as great as the diameter of the anode, as shown in the figure. This design, it has been found, gives the anode much more influence on the a0- 15 celeration of the electrons from the cathode, but still assures that nearly all the current will flow to the grid. Externally of the envelope and surrounding it, is some suitable means, such as a coil winding, for creating a magnetic field 20 parallel with the cathode.

In the operation of this magnetron, both the grid structure I3 and the anode l2 are positively charged, as shown in Figure 2. When the cathode II is maintained at a suitable incandescence by a heating current, electrons will, under ordinary circumstances, flow toward the grid l3 and anode l2. When there is no magnetic field, the value of this current is determined by various factors, among which are the impressed voltage, the 3 cathode temperature, the size and geometrical relations of the electrodes, and the resistance of any output circuit which may be connected to the electrodes. The electrons which carry or con stitute this current travel outwardly in straight 35 radial paths from the cathode to the surrounding grid I3 and anode l2, and most of them will fall upon the anode. However, when a magnetic field is applied substantially parallel to the cathode and hence substantially at right angles to the 40 electric field between the electrodes, then the electrons are deflected and caused to travel in a spiral path about the cathode on their way to the grid, as shown by dotted lines in Figure 1. As the field strength is increased, the fiow of cur- 4,5 rent to the anode ceases altogether for relatively weak fields because the vane-like elements of the grid structure completely cut off the paths of the electrons as the spiral paths of the electrons become longer; finally at a rather critical magnetic field strength, characteristic of any particular device, some of the electrons fail to reach the grid structure 13 by reason of this deflection, thereby resulting in a decrease of grid current. When the field strength is still further increased, above this critical value, the electron current rapidly falls and is finally reduced substantially to zero. It is proposed in the present invention to adjust the value of the field strength so that the electrons reach the grid structure only, while substantially no current flows to the anode and it is under these circumstances that any variations in anode potential will vary the amount of grid current without any flow of current to the anode. By means of these tubes one may obtain a voltage amplification factor of 2 or 3 to one, or even more, depending upon the design of the tube and circuits.

Figure 2 shows an amplifier circuit using a chain of electron discharge devices I, 2 and 3 in accordance with the present invention. These devices may be either the magnetron illustrated in Figure 1 or any suitable three element tube provided with coil windings, as shown. The grid or control electrode of each tube is shown connected to the anode of the next succeeding tube, these electrodes both being supplied with equal positive potentials through impedances or resistances R from a source such as a generator, battery or rectifier.

In the operation of this circuit, variations in signal current received over an input circuit 5, which is illustrative of any desired receiving or transmitting arrangement, are applied to the anode of tube I, thus causing variations in the amount of grid current without having any flow of current to the anode. Such variations in grid current of tube l in accordance with the incoming signal waves cause a variation in voltage drop (IR) to appear in impedance R in circuit with the grid, and consequently a variation in the potential on the anode of electron discharge device 2 which, in turn, influences the grid current flowing in the circuit of electron discharge device 2 similar to that heretofore described, and so forth. The output circuit which is shown connected to electron discharge device 3 and any suitable utilization circuit 6 will contain fluctuations in current similar to those appearing in the input circuit 5, except that they have been amplified by each of the succeeding tubes I, 2 and 3. If the vacuum tubes are properly designed, the output potential, current and power from the system may be made much greater than the input.

An arrangement as just described in connection with Figure 2 may be used for amplification of frequencies from about 20 to 1,000,000 cycles with high eficiency and should find a large field of usefulness in the transmission of television signals.

Figure 3 shows a cascade resistance or impedance coupled amplifier system using split anode magnetron tubes 20, 2!, and 22. In this system equal direct current potentials are preferably applied to the control and output anode elements of the same tube. The split anode magnetron tube, due to the curved paths taken. by electrons in the magnetic field, has the peculiar property of increasing the current flow to one anode when the potential of the other electrode is increased and vice versa. If I trace the paths of the electrons, it will thus be seen that with equal positive potentials on both anodes of the tube and with a critical value of field, no electrons will flow to either anode element in the absence of input signals, but that with an increase in the positive potential to the control anode element due to a received signal, electrons will start to flow toward the control anode element but will reach only the output anode element on account of the radial paths of the electrons. Thus, fluctuations in potential applied to one anode cause fluctuations in the current flowing to the other anode. In Figure 3, one anode of each tube is shown so connected that it serves as an input electrode while the other anode serves as an output electrode.

Since the two anodes are usually identical in size and construction and symmetrically located with respect to the cathode, it might, at first thought, appear that no voltage gain can be obtained with the system. However, this is not the case since the interaction or regeneration effect of the applied alternating current energy of the magnetron enters into consideration and may cause a large voltage gain per tube. This may be explained as follows: If the anode used as a control electrode has its potential made more positive, the result is an increase in current to the other electrode. Due to increased voltage drop in the series or coupling impedance of the'other electrode, its potential is decreased. This, in turn, tends to reduce the current to the control electrode. Thus increased control grid potential results in decreased control grid current, which is equivalent to regeneration or negative input resistance. With associated circuits having insufficient loading due to positive resistance, this regeneration or negative resistance efiect can and does produce oscillation between the two electrodes at any frequency to which the associated circuits are tuned. In the instant case, it may be assumed that the negative resistance of the tube is balanced, to prevent oscillation, by the positive resistance of the coupling impedances.

Referring to tube 2| in the diagram, let us assume that, due to the action of the first tube, anode 23 has its potential increased. At once the current flow to electrode 24 is increased and this reduces the potential of 24 by increasing the voltage drop in impedance Z". But reducing the potential of 24 reduces the current flow to 23, raising-its potential still higher, and so there is' effective regeneration without frequency discrimination if the coupling impedances are resistances. The presence of regeneration is apparent from the fact that the split anode magnetron, when adjusted for equal average current flow to both electrodes, is regenerative and capable of producing oscillations at any frequency to which the electrodes will respond. In other words, the split anode magnetron has a push-pull negative resistance. If the coupling resistances are made to be equal to one another, or somewhat less than the efiective alternating current negative resistance, then there is obtained very great power amplification. By suitable circuit and tube adjustments the voltage, current and power gain per tube may be made quite high and can approach infinity.

Figure 4 is similar to Figure 3 except that a push-pull arrangement is illustrated in which couplings between output and input circuits are neutralized, and more complex interstage coupling circuits are provided to widen the frequency response characteristic. Due to these extra complications it is possible to obtain substantially equal amplification for all frequencies in an extremely large band from, say 0 to 2,500,000 cycles. Of course, the type of tube illustrated in Figure 2, or any other positive control grid type of tube may be used in this system.

Although there are shown circuits suitable for amplification of relatively low frequencies, it will be understood that my positive potential control element system may also be used for radio frequency amplification by substituting tuned circuits in place of the interstage coupling impedances shown in the drawings.

I claim:

1. The combination with an electron discharge magnetron tube including an electron emitting cathode, a grid surrounding said cathode, and a control electrode surrounding said grid, means for supplying substantially equal positive direct current potentials to said grid and control electrodes, and means for applying a magnetic field to said electrodes having a component at right angles to the electric field between said electrodes.

2. In combination, an electron discharge device including a cathode, a control and a controlled electrode, both said control and controlled electrodes. extending along an appreciable portion of the effective length of said cathode, means for maintaining both control and controlled electrodes at positive potentials relative to said cathode. an input circuit coupled to said control electrode and cathode and an output circuit coupled to said controlled electrode and cathode, and means for applying a magnetic field to said electrodes of such a value that controllable electron current flows to the controlled electrode but substantially no electron current flows to the control electrode upon receipt of signals from said input circuit.

3. An amplifier circuit comprising a vacuum tube having an imperforate control electrode, a cathode, and a perforate controlled electrode, said control and controlled electrodes extending along an appreciable portion of the eiTective length of said cathode, means for maintaining said control and controlled electrodes at positive potentials with respect to said cathode, an input circuit coupled to said control electrode and an output circuit coupled to said controlled electrode.

4. A regenerative amplifier comprising a split anode magnetron having a cathode and a pair of anodes extending along an appreciable portion of the effective length of said cathode, an input circuit connected to one anode, and an output circuit connected to the other anode.

5. A cascade amplifier system comprising a plurality of split anode magnetrons in series relation, each having a cathode and a plurality of anodes extending along an appreciable portion of the effective length of said cathode, an input circuit connected to one anode of each magnetron, and an output circuit connected to another anode of the same magnetron.

6. In combination, an electron discharge device comprising an envelope containing a control electrode, a grid, and a cathode, said control electrode and grid extending along an appreciable portion of the efiective length of said cathode, a magnetic field surrounding said envelope, means to apply approximately equal high positive potentials to both said control electrode and grid, an input circuit coupled to said control electrode, and an output circuit coupled to said grid.

'7. In combination, an electron discharge device amplifier comprising an envelope containing a control electrode, a grid, and a cathode, said control electrode and grid extending along an appreciable portion of the effective length of said cathode, means to apply approximately equal high positive potentials to both said control electrode and grid, a magnetic field parallel to said cathode whereby current to said control electrode is reduced to zero and current flows to the grid, means to vary the positive potential on said control electrode in accordance with the signal to be amplified, and utilization means coupled to said grid.

8. An amplifier having, in combination, a first electron discharge device comprising a control electrode, cathode and grid, said control electrode and grid extending along an appreciable portion of the efiective length of said cathode, and a magnetic field surrounding said electrodes, a second electron discharge device similarly arranged, a direct wire connection between the grid of said first device and the control electrode of said second device, means for supplying over separate paths a positive potential to said wire connection and to the control electrode of the first device and to the grid of said second device, an input circuit connected to the control electrode of said first device and an output circuit coupled to the grid of said second device.

9. A regenerative amplifier comprising a split anode magnetron having a cathode and a pair of anodes oppositely disposed with respect to and extending along an appreciable portion of the effective length of said cathode, an input circuit connected to one anode and an output circuit connected to the other anode, and means for applying positive potentials to both of said anodes.

10. In combination, an electron discharge de vice having a cathode, a grid electrode surrounding said cathode, and a control electrode surrounding said grid, means for supplying positive potentials to said grid and control electrodes with respect to said cathode, an input circuit coupled to said control electrode, and an output circuit coupled to said grid electrode.

11. In combination, an electron discharge device having a cathode, a grid electrode surrounding said cathode, and a control electrode surrounding said grid, means for supplying positive potentials to said grid and control electrodes with respect to said cathode, means for applying a magnetic field parallel to said cathode, an input circuit coupled to said control electrode, and an output circuit coupled to said grid.

12. In combination, an electron discharge device comprising an evacuated envelope having within it a pair of anodes oppositely disposed with respect to a central cathode located between said anodes, a coil surrounding said envelope for applying a magnetic field parallel to said cathode, an input circuit coupled to one of said anodes, and an output circuit coupled to the other of said anodes.

13. In combination, an electron discharge device comprising an evacuated envelope having within it a pair of anodes oppositely disposed.

with respect to a central cathode located between said anodes, a coil surrounding said envelope for applying a. magnetic field parallel to said cathode, means for applying positive potentials to both said anodes, an input circuit coupled to one of said anodes, and an output circuit coupled to the other of said anodes.

14. In combination, an electron discharge device comprising an evacuated envelope having within it a control anode and a controlled anode oppositely disposed with respect to a central cathode located between said anodes, a coil surrounding said envelope for applying a magnetic field parallel to said cathode, a second similar electron discharge device, a neutralization circuit coupling the control anode of each device with the controlled anode of the associated device, a connection between the cathodes of both devices, means for applying positive potentials to the control anodes of both devices, an input circuit connected to the control anodes of both devices, and a utilization circuit coupled to the controlled anodes of both devices.

15. In combination, an electron discharge device comprising an evacuated envelope having within it a control anode and a controlled anode oppositely disposed with respect to a central cathode located between said anodes, a coil surrounding said envelope for applying a magnetic field parallel to said cathode, a second similar electron discharge device, a neutralization circuit coupling the control anode of each device with the controlled anode of the associated device, a connection between the cathodes of both devices, means for applying positive potentials to the control and controlled anodes of both devices, an input circuit coupled to the control anodes of said devices, and a utilization circuit coupled to the controlled anode of said devices.

16. The method of operating an electron discharge device having a cathode, a control and a controlled electrode, both extending along an appreciable portion of the effective length of said cathode, which comprises maintaining both said control and controlled electrodes at substantially equal positive potentials with respect to said cathode and applying a magnetic field to said device parallel to said cathode of such a value that an increase in positive potential to said control electrode will cause electrons emanating from said cathode to impinge solely on said controlled electrode.

17. In combination, an electron discharge device including a cathode, a control and a controlled electrode each in the form of a cylinder surrounding said cathode for an appreciable portion of the effective length thereof, said controlled electrode being perforated and located intermediate said cathode and control electrode, means for maintaining both control and controlled electrodes at positive potentials relative to said cathode, an input circuit coupled between said control electrode and cathode, an output circuit coupled between said controlled electrode and cathode, and means for applying a magnetic field to said electrodes of such a value that controllable electron current flows to the controlled electrode but substantially no electron current flows to the control electrode upon receipt of signals from said input circuit.

18. An amplifier system having, in combination, first and second electron discharge devices each having a cathode, a grid surrounding said cathode and an anode surrounding said grid, a coil surrounding each device for producing a magnetic field in a direction parallel to the oathode thereof, a source of signals coupled to the anode of said first device, a direct connection between the grid of said first device and the anode of said second device, an output circuit coupled to the grid of said second device, and means for applying direct current potentials to said anodes and grids which are positive with respect to their associated cathodes.

CLARENCE; W. HANSELL.