US1872274A - Thermionic tube - Google Patents

Description

Aug 16, 1932- T. R. GOLDSBOROUGH THERMIONIC TUBE Filed March 27, 1928 INVENTOR fiwwf TTORNEY Patented Aug. 16, 1932 UNi'l'ED STATES PATENT OFFICE TEADDE'US R. GOLDSBOROUGH, OF FOREST HILLS, PENNSYLVANIA, ASSIGNOB TO WEST- INGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION 01E PENN- SYLVANIA THERMIONIC TUBE Application filed March 27, 1928. Serial No. 265,017.

My invention relates to thermionic devices, and it has particular relation to thermionic amplifier tubes of the equipotential-cathode yp In the patent to Nicolson, No. 1,459,412 is disclosed a thermionic tube having an equipotential cathode comprising an insulating ody coated with electron-emissive oxides and provided with an internal heating element for raisin the oxides to the temperature at which they come thermionically active. Although the patent discloses the use of a battery for supplying potential to the cathode-heating element, it is now customary in the art to utilize alternating current for this purpose, reliance being placed on the thermal lag in the insulating body to prevent the presence of hum in the output of the tube.

Anode, or plate, potential for tubes of the type to which my invention pertains is usually supplied either from batteries, or from a separate source of rectified alternating current, when such tubes are utilized in radioreceiving apparatus. The use of batteries, or separate rectifiers, while satisfactory in situations where their weight is not objectionable, is not advisable in airplane receivers or transmitters, however, nor in any other situation where both space and weight must be economized.

It is, accordingly, one object of my invention to provide a thermionic device which shall require neither batteries nor auxiliary rectifiers for the supply of operating energy thereto.

Another object of my invention is to provide a combined thermionic amplifier tube and rectifier that shall be capable of being entirely energized from a source of commercial, or other, frequency alternating current.

Another object of my invention is to provide a combined thermionic amplifier tube and rectifier that shall have incorporated therein means for shielding the amplifier portion thereof from magnetic effects produced by the rectifier portion.

Another object of my invention is to provide a combined thermionic amplifier tube and rectifier that shall utilize a single heating element for both the amplifier portion and the rectifier portion thereof.

Another object of my invention is to provide, in a combined thermionic amplifier tube and rectifier, a rectifier portionthat :hall utilize a cathode of the equipotential Another object of my invention is to provide in a combined thermionic amplifier tube and rectifier, means for controlling the rectifying action of the rectifier portion thereof.

Another object of my invention is to provide a device of the aforementioned type that shall be capable of being utilized as a generator of osc1llations at any desired frequency. as an amplifier, or as r dectector.

Another object of my invention is to pro vide a device of the aforementioned type that shall be capable of being entirely energized from a source of alternating current of commercial, or other, frequency, without the manifestation of objectionable hum in the output circuit thereof.

Another, and more specific, object of my invention 'is to provide a circuit network of a novel type, particularly adapted to connect my combined rectifier-amplifier to a source of alternating current.

A combined thermionic amplifier and rectifier device constructed according to 'my invention preferably comprises a single cathode-heating element for both the amplifier portion and the rectifier portion thereof. The cathode of the rectifier portion is so constructed and arranged that it, of itself, without other metallic elements intervening, may serve as the anode for the amplifier portion of the device, and has the additional function of shielding the said amplifier portion from electromagnetic disturbance from the rectifier ortion.-

In ad ition, I have found it distinctly advanta eous, though not strictly necessary, to provi e means for, in part, neutralizing the space-char e in the rectifier portion. uch means pre erably takes the form of a grldelement interposed between the anodes and the cathode constituting the rectifier, in combination with means for impressing any desired bias-potential thereon with reference to the said cathode.

The novel features that I consider characteristic of my invention are set forth wlth articularity in the appended claims. The invention itself, however, both asto its organization and its method of operatlon, together with certain further objects and advantages thereof, will best be understood by reference to the following description of a specific embodiment, taken with the accompanying drawing.

The single figure of the drawing 1s a view in perspective of a preferred form of my combined amplifier-rectifier tube, certain of the elements thereof being broken away to more clearly show the interior structure of the device, together with a diagrammatic view of the circuit network Iprefertoemploy for energizing the tube when it is utilized in radio reception.

The combined amplifier-rectifier tube comprises an evacuated glass envelope 1 in whlch an elongated element 2, of porcelain, or the like, is axiall mounted. A plurality of openings 3 an 4 extend from end to end of the element 2, through which openings is threaded a loop 5 of resistance wire. The loop 5 is provided with terminals 6 and 7 that extend through the end of the envelope 1, and are connected respectively to the terminals of a seconda winding 8 of a power transformer 10. he rimary winding 11 of the transformer may e energized from any convenient source of alternating current.

A cylindrical metallic sheath 12, substantially coextensive with the elongated element 2, and having an enlarged bell-shape lower end 13, is fittedover the said element, and in close contact therewith for the major portion of its length. The exterior surface of the upper ortion of the sheath 12 having the lesser iameter is coated with thermionicall active oxides, and functions as a cathode wit. respect to a plurality of cylindrical anodes 14 and 15 which encircle it.

The anodes 14 and 15 are provided with terminals 16 and 17, respectively, which extend through the end of the envelope and are connected to the terminals of a secondary high potential, winding 18 carried by the power transformer 10.

A grid, or space-charge-controlling, element 20 is disposed intermediate the oxide-coated upper portion of the metallic sheath and the .onically active oxides.

anodes 14 and 15, and is provided with terminal 21 which extends through the en unctions to lower the internal impedance of the rectifier portion of the device.

Although the grid 20 is not essential to the operativeness of my combined amplifierrectifier, it is decidedly advantageous.

A relatively short metallic sheath 24 is disposed around the lower end of the heater element 2 adjacent to the enlarged portion 13 of the long metallic sheath 12, which sheath 24 also carries an exterior coating of theremi- The short sheath may, if desirable, be replaced by a metallic film electro-plated on the element 2, or by any other conductive coating in good thermal contact with the said element' A grid 25 is disposed around the short sheath 24, intermediate it and the enlarged portion 13 of the long sheath 12, and has the usual function of the grid in thermionic amplifier tubes of well-known types.

The long sheath 12, the short sheath 24, and the grid 25 are provided with terminals 26, 27, and'28, respectively, which extend through the lower end of envelope and are conductively connected to corresponding pins 30, 31 and 32 carried by a base member 33 into which the lower end of the envelope is cemented.

An input circuit is provided for the amplifier portion of the device, which circuit, if the device is to functon as a combined rectifier and detector, comprises an inductor 34 having a tuning condenser 35 connected in shunt thereto. One end of the inductor is connected through a grid leak 36 and grid condenser 37 to the pin 32, which pin, in turn, is electrically connected to the grid 25. The opposite end of the inductor is connected to the short sheath 24, which constitutes the cathode of the amplifier tube portion.

The input circuit may be coupled to a radiant energy receiving device comprising an antenna 38, a coupling inductor 40, and a ground connection 41.

The output circuit of the amplifier tube portion of the device may be traced from the mtermediate point 23 of the secondary winding 18, through a conductor 42 to a filter circuit comprisin a plurality of choke coils 43, the primary winding 44 of an output transformer 45, and then through a conductor 46 which is connected to the cathode 24. Each of the choke coils has a bypass condenser 47 connected in shunt thereto, the said condensers having a common terminal which is conductively connected to the pin 30 by way of a conductor 48 and consequently to the elongated sheath member 12.

The secondary winding of the output transformer 45 may be connected to a fpair of telephones 50, as shown, or it ma orm the input circuit to a second combine recti- I energized from the secondary winding 8 and serves to raise the upper end of the elongated sheath member 12 to such a temperature that the oxide coating on the exterior surface thereof emits electrons. Y i

The electrodes 14 and 15, bein connected to o posite terminals of the hig potential win ing 18 constitute a full-wave rectifier with the upper or cathode, end of the sheath element 12. The space char e between the said electrodes and the oath e may be neutralized to a greater or less extent b ad'usting the potential applied to the gri 20 rom the biasing source 22. Ifthis potential is made sufliciently positive the impedance of the rectifier (portion of the device may be considerably re uced. v

The rectified current, which will have a double-frequency component, flows down through the sheath member to the bell shape portion thereof, or to the se arate bell shape electrode if such an electro e is utilized, and from it across to the short sheath 24 which constitutes the cathode for the amplifier portion of the device.

The grid 25 in the amplifier portion has the usual and well known function of controlling the flow of space current between the anode and cathode. If, as shown, the device is utilized as a detector, the grid will acquire negative charges dependent upon the size of the grid leak and grid condenser and u on the amplitude of the incoming signals. he operation of the amplifier portion, therefore, differs in no way from the operation of other similar thermionic tubes.

The direct current com onent of the output current flows back to t e midpoint on the high potential secondary winding over the, path previously traced, which path includes the primary winding of the out ut transformer. The cycle and 120 cyc e com onents of the current rectified in the recti er portion of the device are bypassed back to network arranged for its ener ation the amount of hum in the output clrcuit of the m llifier portion thereof is substantially neggl e.

Although the device has been illustrated as applied to the detection of incoming radiofr uency signals it may, of course, be utilize for their amplification at radio frequencies instead, if desired.

By employin a cathode of the equipotential type inbot the rectifier and am lifier portions of my improved thermionic evice, and by providing sufiicient thermal-la in the insulating supporting elemelft '2 t rough which the heatlng wires extend, the hum re sulting from varying cathode temperature is materially reduced.

In'addition, inasmuch as the lower end'of the long sheath 12 is interposed between the rectifier and amplifier portions of the device, the said amplifier portion is effectively shielded against magnetic disturbances arising in the rectifierportion. The long sheath, or atleast the bell sha ed ortion thereof, should preferably be ma e o a magnetic material in order to more effectively serve as a screen.

Although I have illustrated and described a specific embodiment of my invention, various modifications thereof and various modifications of the energizing circuits therefor will be apparent to those skilled in the art. My invention is, therefore, not to be limited except insofar as is necessitated by the prior art or by the spirit of the appended claims.

I claim as my invention:

1. A unitary thermionic device comprising an evacuated envelope, elements constituting a rectifier and a radio valve, three of said elements common to said rectifier and said valve, one of said three elements constituting a heater unit and another of said three elements constituting an insulating member surrounding said heater unit.

2. A combined thermionic rectifier and am plifier comprising an evacuated envelope enclosing a heating element, a thermionically active elementadapted to be heated by said heating element, a plurality of electrodes adapted to cooperate with said active element to constitute a rectifier, and a second thermionically active element adapted to cooperate with said heating element and said first mentioned active element and with a control electrode to constitute a radio valve. 3. A combined thermionic rectifier and amplifier comprising an evacuated vessel enclosing a plurality of electrically distinct thermionically afiive elements, and a plurality of electrodes mounted to cooperate with one of said elements to constitute a rectifier therewith, the last-mentioned element constituting an anode for the amplifier.

4. A combined thermionic rectifier and amplifier comprising a plurality of complete triode units, means for shielding the amplifier unit from the rectifier unit, said scribed my name this 19th dag of March1928.

shielding means contituting an anode for said amplifier portion.

5. A combined thermionic rectifier and amplifier, including a plurality of thermionicall active elements and a plurality of elect es, a heating device common to said active elements, means adjacent one of said active elements constituting a rectifier therewith, and means for conducting the rectified current to the amplifier portion of the device said last-named means comprising a shield for preventing inductive interference between the rectifier and the amplifier portion.

Intestimony whereof, I have hereunto sub- THADDEUS R. GOLD BOROU

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