US1850104A

US1850104A - System for eliminating tube noise

Info

Publication number: US1850104A
Application number: US400490A
Authority: US
Inventors: Clarence W Hansell
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1929-10-18
Filing date: 1929-10-18
Publication date: 1932-03-22
Anticipated expiration: 1949-03-22
Also published as: GB360630A

Description

22, 1932. c. w. HANSELL 1,850,1Q4

SYSTEM FOR ELIMINATING TUBE NOISE Filed Oct. 18, 1929 INVENTOR CLARENCE W. HANSELL ATTORNI IY Patented Mar. 22, 1932 CLARENCE W. HAN SELL, OF PORT JEFFERSON, NEW YORK, ASSIGNOB TO RADIO COB- PORAIION OF AMERICA, A CORPORATION OF DELAWARE SYSTEM FOR ELIMINATIN G TUBE NOISE Application filed October 18, 1928. Serial No. 400,490.

My present invention relates to amplifiers,

and, more particularly, to amplifier circuits embodying electron discharge devices of novel construction, the amplifier circuits being such that the, amplified output is much less afi'ected by undesired emission variations, than the circuits now in common use.

A factor which causes considerable difliculty in operating an amplifier embodying electron discharge tubes is the noise produced by the tubes themselves. It will be obvious that the slightest variation in the currents flowing in the plate to filament circuit of an amplifier tube, may be so magnified, particularly if it be a tube in one of the first stages of a multistage amplifier, as to result in an extremely large variation in the anode current of the last stage. This large variation in the last stage is usually detected in the form of a hissing or rushing sound, which is sometimes called tube noise or tube hiss.

In many cases, particularly at very high frequencies, these disturbing noises are loud er than atmospheric noises and are the fundamental limitation in very high frequency radio reception. If they could be eliminated the distances at which very high frequency transmitters might be heard would be great- 1y increased, the transmitter power could be reduced, or the quality of reception would be improved. It has been determined that these minute variations of current in the tube circuits occur because of several causes, one of the most common of which causes is actual irregularities in the rate of emission of electrons from the tube cathodes. It has been stated by Hull that the upper limit of amplification is about 2X 10 in voltage; the actual irregularities in electron emission making greater amplification useless.

It has, therefore, been concluded by many that because of the surface conditions of the hot cathode from which the electrons are being boiled out, it seems impossible that the emission of the electrons could be made steady enough to eliminate a slight irregularity. Efforts, consequently, towards correcting and eliminating this irregularity have been directed towards increasing the ratio between signal strength and tube noise, rather than the elimination of the tube noise itself.

Now, I have invented a method of eliminating noise in the output of an amplifier, which noise is due to variations in cathode emission, or variations in anode or grid potential, my method, thus, permitting greater radio frequency amplification to be used so that smaller values of radio frequency energy may be amplified successfully. I have also devised means for embodying my invention in a practical form, and applying it in an amplifier circuit.

Accordingly, it is one of the main objects of my present invention to provide a method of, and means for, eliminating tube noises in the final output of high frequency energy amplifiers, the said means including an elec-' tron discharge tube embodying an anode circuit arranged in such a manner that any vari ations in emission from the tube cathode or any variations in anode and grid power supply potentials will result in equal and opposite variations in the said anode circuit, with the result that no tube noise will be impressed upon the input of a subsequent stage.

Another important object of the present invention is to provide an amplifier circuit for high frequency energy, which circuit includes an electron discharge tube comprising an electron emission source, and a plurality of anodes electrostatically shielded from the said source, the anodes being connected in such a manner that variations in emission from the said source will result in equal and opposite variations in the anode output circuit whereby the said currents will balance out and no noise be present in the output of said amplifier.

' Another important object of the invention is to provide an electron discharge tube capable of greatly amplifying radio frequency currents when arranged in an amplifier circuit connected for eliminating noises due to variations in cathode emission, the tube comprising a cathode, a pair of anodes electrostatically shielded from the cathode, all points on the cathode being substantially equi-distant from the two anodes, and one or more control electrodes symmetrically disposed with respect to the anodes and cathode and causin deflections in the electron stream, the amplifi cation of the tube being a maximum when the active length of the control electrodes is approximately equal to a half wave for the frequency being amplified.

Other objects of the invention are to amprove generally the efiiciency of amplifier circuits embodying electron discharge devices, and to, further, provide an electron discharge tube which is durable and reliable in operation, possesses high amplification power, a minimum of reaction from the output circuit back to the input circuit, and may be readily arranged in an amplifier circuit to eliminate tube noises arising from irregularities in cathode emission.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically one circuit organization whereby my invention may be carried into effect.

Referring to the accompanying drawing, there is shown astage of tuned radio frequency amplification having its tuned input circuit 1, 2, coupled, at at M to a source of radio frequency energy, the latter being generally designated as input. The tuned output circuit 3, 4., of the radio stage is coupled, as at M to any utilization circuit, generally designated as output.

I will now describe, in detail, the manner in which a tube, constructed according to novel principles, may be arranged between the tuned input and output circuits to eliminate tube noises in the output. A tube consists of three insulating sections 5, 6 and 7. Section 5 has sealed in it the cathode of filament 8, the latter being heated by a source of current A.

A pair of anodes 9, 9 are disposed adjacent an opening in insulating section 7. the said opening being closed by a screen grid or electrostatic shielding member 10. The shield 10 is retained in parallelism with the anodes 9, 9, by a metal cylinder 11, the latter having its opposite ends sealed to insulating sections 6 and 7.

A second metal cylinder 12, has its opposite ends sealed to insulating sections 5 and 6. If preferred the cylinder 12 may be supported inside the envelope of the tube and insulating sections 5 and 6 may be joined into one section of insulating envelope. A pair of

wires

13 and 13, having the greater portion of their length substantially parallel, are sealed to the section 5 at an end thereof. In order to mount the tube an annular, metallic mounting and shielding disc 14 is provided, the inner circumference of the disc contacting with the exterior of the cylinder 11. This disc, when the tube is in operation serves to cover the opening, between two shielded compartments containing the input and output circuits so that there is no reaction from the output circuit back into the input circuit due to electrostatic or electromagnetic coupling.

The disc 14 is further provided, adjacent its outer circumference, with a plurality of mounting apertures 15. Thus, in orderto fixedly mount a tube within a receiving set it is merely necessary to employ the apertures 15 for receiving the securing means which shall fixedly maintain the disc 14 in a given position. In this tube, the two anodes 9 and 9 are electrostatically shielded from all other parts within the tube by the shield grid 10. The two control electrodes 13 and 13' are symmetrically spaced with respect to the anodes and the filament 8. It should be understood that only one control electrode can be employed, if desired.

The filament 8 is designed with a relatively large surface area, and a low heating temperature should be used to minimize at the beginning the amount of emission variation, the eflects of which we wish to reduce or eliminate. Furthermore, all points on the filament should be as nearly as possible equidistant trom the two anodes 9 and 9 so that emission variations, which occur in spots, or unequally over the cathode area are more nearly balanced in their efiect upon the two anodes. I will now describe the connections between the tube, the tuned input circuit and the tuned output circuit which will eliminate noise resulting from variations in cathode emission, and which will permit more variations in plate and grid voltages. I

Positive potential is applied to the screen grid 10 and the anodes 9 and 9 of the tube from current sources D and B respectively. The positive terminal of the source B is connected by a lead 15 to the midpoint of inductance coil 3. A lead 16 connects the positive terminal of source D to the shielded disc 14. The midpoint of the filament heating source A is connected by a lead 17 to ground, it being observed. that the sources B, C, D and E are also grounded.

The

control electrodes

13 and 13 are negatively biased by means of a lead 18 connected between the negative terminal of the source C and the mid-point of inductance coil 1. The metallic cylinder 12 has negative potential applied to it for concentrating the electronic stream issuing from the filament 8, by means of a lead 19 connected between the gegative terminal of source E and the cylin- I have represented the center of the electronic stream issuing from the cathode or filament 8 by means of a series of dotted lines 20 passing between the

control electrodes

13 and 13. The middle of these lines shows the position of the stream when there is no energy in the input circuits while the outer lines show the positions to which the stream may be deflected when there is an input. The stream is deflected back and forth between the anodes 9 and 9' b the alternating potentials on the contro electrodes, it being understood that the latter elements are connected in circuit with the variable condenser 4 and the inductance coil 3 in the tuned output circuit of the stage.

When positive potential is appliedto-the screen grid and anodes of the tube, and there is no energy in the input circuit, substantially equal currents will flow to the two anodes and any variations in emission from the filament, with their corresponding variations in plate to filament and grid to filament potential, will cause equal variations .in the two anode currents. The output from the anodes being connected, as shown, in

' push-pull manner, it therefore results that the equal variations in the anode currents due to the usual source of tube noise will balance out, and no noise will be heard in the output circuit.

The two control electrodes have their potentials varied by the radio frequency currents which are to be amplified, and, as a result, will cause deflections in the electron stream 20 similar to those in the cathode ray oscillograph. These deflections of the stream will vary the anode currents diiferentially, and the differential variations will produce the useful amplified output from the tube.

Of course, when the tube is amplifying there may be slight variations in the unbalanced component of anode current which will slightly modulate the amplified alternating currents, but this efl'ect will be of a relatively small magnitude and is negligible in comparison with the efi'ect of emission variations in the types of vacuum tubes now in common use.

It should be possible to get a very large amplification with a tube as described heretofore, up to frequencies where the time required for an electron to travel the length of the control electrodes, approaches the duration of one cycle. Long control electrodes will increase the amplification up to the point where the time of travel of the electrons becomes an appreciable factor, or up to the point where the action length of the control electrodes becomes equal to a half wave for the frequency being amplified.

It will thus be seen, that I have discovered a new method, and devised novel means for, effectively eliminating tube noises in the output circuits of the amplifiers, which noises arise because of cathode emission variations or variations in power supply voltages, the method essentially consisting in balancing out anode currents arising because of the said emission variations and simultaneously.

differentially varying the path of an electron stream between the cathode and anode by radio frequency currents'to be amplified, in

order to produce useful variation in anode output. It is also to be observed th'atthe type of tube' describedmay be used for direct current amplification, alternating cur-.

rent amplification, and also as a detector.

It should also he understood that while I have indicated and described one arrange ment for carrying my invention into eflect, it will be apparent to one skilled in the art that my invention is by no means limited tothe particular organization shown and described, but that many modifications may be employed without departing from the scope of my invention as set forth in the appended claims. 'In particular I wish .to point'out that the detail proportions and construction of the vacuum tube shown will undoubtedly be modified by careful considerations of detail design and to permit of constructing the tube with less practical difiiculties. The fig-' ure is only intended to illustrate the general schgme and I, arrangement which would be use What I claim is:

1. An electron discharge tube com rising an evacuated casing, a pairof ano es'disposed therein, a cathode disposed within said casing, all points on the cathode being substantially equi-distant from the two anodes, one or more control electrodes disposed within the casing for deflecting the path of electrons flowing between the cathode and anodes and an electrostatic shield between the anodes and the remaining electrodes within the cas-. mg. i 1

2. An electron discharge device for am lifying radio frequency currents comprising an enveloping member, a pair of anodes disposed withinsaid member, a cathode within said member, one or more control electrodes disposed within the member and symmetrically spaced with respect to the anodes-and. cathodes, a screen grid between the anodes and the remaining electrodes within the ing electrode in the path of the electrons flowing from the cathode to the anode, maintained at a predetermined potential.

4. In apparatus for undulatory electrical currents, an envelope, an anode within the envelope, a cathode within the envelope for supplying a stream of electrons to flow to the anode, a deflecting electrode within the envelope intermediate the anode and cathode for deflecting the stream of electrons flowing' the anode, a deflecting electrode within the envelope intermediate the anode and cathode for deflecting the stream of electrons flowing between the anode and cathode, and, an auxiliary electrode adjacent the anode for substantially eliminating feed-back from the anode to other electrodes within the envelope.

6. Apparatus for undulatory electrical currents comprising, an envelope, a pair of anodes within the envelope, a cathode for supplying a stream of electrons within the envelope, one or more deflecting electrodes within the envelopefor deflecting the stream of electrons'flowing from the cathode towards the anodes, and, a screening electrode in the path of the electrons flowing from the cathode towards the anodes maintained at a suitable potential.

7. An electron discharge device for undu latory electrical currents comprising, an envelope, a cathode within the envelope for supplying electrons, an anode within the envelope for receiving electrons supplied by the cathode,'and a negatively charged electrode intermediate the anode and cathode for concentrating the electrons flowing from the cathode to the anode into a relativelysmall stream.

'8. An electron discharge device for undulatory electrical currents comprising, an envelope, an anode within the envelope, a cathode within the envelope for supplying a stream of electrons to the anode, and, a negatively charged electrode intermediate the anode and cathode about the stream of electrons flowing from the cathode to the anode for concentrating the stream of electrons so flowing.

9. An electron discharge device for undulatory electrical currents, comprising an envelope, an anode within the envelope, a cathode within the envelope for supplying a stream of electrons to the anode, a cylindrical electrode about the stream subjected to a negative potential for concentrating the stream of electrons flowing from the cathode to the anode, a deflecting electrode adjacent the stream for deflecting the stream in accordance with potentials supplied tothe electrode, and, a screening electrode subjected to unidirectional potential in the path of the stream.

10. An electron discharge device for undulatory electrical currents comprising, an

envelope, 2. pair of anodes Within the en velope, a cathode for supplying a stream of electrons to flow to the anodes, deflecting electrodes adjacent the stream for causing the stream to flow alternately from one anode to the other, a cylindrical electrode about the stream subjected to a negative potential for .concentrating the stream of electrons flowing to the anodes, and, an auxiliary electrode subjected to unidirectional potential adjacent the anode.

11. An electron discharge device for undulatory. electrical currents comprising, an

envelope, a pair of anodes Within the en-. velope, a cathode for supplying a stream of electrons to flow to the anodes, deflecting electrodes adjacent the stream for causing the stream to flow alternately from one anode to the other, a cylindrical electrode about the stream subjected to a negative potential for concentrating the stream of electrons flowing to the anodes, and, a screening elect-rode in the path of the stream between the anode and cathode, said screening electrode being subjected to a suitable unidirectional potential.

12. An electron discharge device for undulatory electrical currents comprising, an envelope, a pair of anodes within the envelope, a cathode for supplying a stream of electrons to the anodes, a pair of deflecting electrodes within the envelope for deflecting the stream from one anode to the other alternately, a cylindrical electrode about the stream subjected to a negative potential for concentrating the stream of electrons flowing from the cathode, and, a screening electrode adjacent. the anode in the path of the electron stream, said screening electrode extending beyond the envelope and adapted to support the envelope and the electrodes contained therein.

CLARENCE W. HANSELL.