US3156844A

US3156844A - Amplifier tube having a thermionic cathode without heater

Info

Publication number: US3156844A
Application number: US53135A
Authority: US
Inventors: Veith Werner
Original assignee: Siemens AG
Current assignee: Siemens and Halske AG; Siemens AG
Priority date: 1959-09-18
Filing date: 1960-08-31
Publication date: 1964-11-10
Anticipated expiration: 1981-11-10
Also published as: DE1129239B; NL255625A

Description

Nov. 10, 1964 AMPLIFIER TUBE w. VEITH 3,156,844

HAVING A THERMIONIC CATHODE WITHOUT HEATER Filed Aug. 31, 1960 United States Patent 3,156,844 AMTPLIFIER HAVING A THERh lifihllfi QATHDE WETHGUT iii LATER Werner Veith, Munich, Germmy, assignor to Siemens Halshe Alrtiengeseiischatt Berlin and Munich, a corporation of Germany Filed Aug. 31, 1960, Ser. No. 53,l35 Claims priority, application Germany Sept. 1'8, 1959 9 Claims. (Cl. 313-305) This invention is concerned with a high vacuum amplifier tube having a thermionic cathode (oxide cathode) without heater.

Amplifier tubes with thermionic cathodes have as compared with transistors among others the considerable drawback that they require additional heating and therefore the presence of an appropriate heating voltage.

The present invention is based upon the following thoughts: In the course of investigations, involving above all the operation of amplifier tubes with thermionic cathodes, there is observed as a disturbing phenomenon the known intermediate layer resistance which appears as a result of the formation of a poorly conducting layer between the metallic support and the emitting oxide mass proper. Such intermediate layer resistance appears in the form of a feedback which is disturbingly noticed particularly in the case of low frequencies and also reduces the life of the tubes since it often constitutes a barrier for the penetration of activators from the nickel support, which are required for the activation. The electron stream emitted from the surface must in any case pass this intermediate layer and produces at the surface a voltage drop and therewith Ioules heat. It is possible to obtain intermediate layers which are so far as the resistance value is concerned so considerable that the heat produced therein by the emission current suflices for maintaining the cathode at a temperature required for the emission even without applying the customary heating by the use of a heater. A stable equilibrium will thereby occur since the intermediate resistance will always increase upon decrease of the temperature, thereby causing again generation of more heat. A firing operation is however required in the case of an amplifier tube equipped with such a cathode, to produce with an initially low emission current flowing over the intermediate resistance layer an initial heat which sutfices for the initiation of the thermal emission.

The object of the invention is to produce a high vacuum amplifier tube with thermionic cathode without the use of the customary heater, which is characterized by simple electrode construction and operates reliably throughout a normal useful life.

This object is realized by the provision, in connection with an amplifier tube of the initially described kind, of a cathode with an artificially produced intermediate layer resistance which is pronounced as compared with a normal oxide cathode, and in which is responsive to passage therethrough of the emission current which is constant during the operation, substantially generated the heat required for the cathode temperature, and by the provision of at least one auxiliary electrode (auxiliary anode) forming with the cathode an auxiliary discharge path for effecting the initial emission. An artificial intermediate layer resistance is for this purpose produced by the provision of an insulating layer between the metallic cathode carrier and the customary emission mass. Substances suitable for this purpose are, for example, aluminum oxide, magnesium oxide or calcium oxide, that is, oxides of the earth alkalior related earth metals. The emission layer is formed by using oxides of earth alkali metals such as barium, strontium and calcium, customarily employed for oxide cathodes, or, in the case of low current,

3,156,844 Patented Nov. 10, 1964 magnesium oxide, which are developed Within the discharge vessel from the corresponding carbonates during the forming operation.

The initial emission for the so-called firing operation may be produced by light-electrical eiiect or by secondary emission at the emission layer proper. A further advantageous possibility for the passage of electrons through the intermediate layer resistance, for achieving the initial heating, resides, according to the invention, in covering the surface of the oxide cathode with several metallic rods and directly connecting thereto, for example, in common, over a very high ohmic resistor the anode voltage or a corresponding positive potential.

The foregoing and further objects and features of the invention will appear from the description which is rendered below with reference to the accompanying drawmg.

Referring now to the drawing, numeral 1 indicates a tubular metallic cathode carrier upon which is provided the intermediate layer 2 carrying the emission layer proper indicated at 3. Directly upon the surface of the emission layer 3 are disposed metallic rods 4in the illustrated example four rodst0 which is connected a very high ohmic resistor 5. The latter is in turn connected to a high voltage of the voltage source, for example, the anode voltage, so as to cause a current to flow between the rods 4 and the cathode carrier 1 which etiects heating of the intermediate layer 2 to an extent sufiicient to cause the emission layer 3 to begin emitting, although initially slightly, at least within the region of the firing anode. The initial heat thus produced flows more and more to the remaining parts of the emission layer 3, for example, between two neighboring metal strips or rods of the auxiliary anode, so that these parts will likewise begin to emit. The working electrode proper assumes thereby and also due to the increasing voltage drop at the high ohmic resistor in the auxiliary discharge path, the emitting electron current which is required for the further heating of the intermediate layer, while the firing voltage lying at the firing anode drops increasingly at the high ohmic resister 5 and exerts no further influence or rather to say no essential influence respectively upon the further emission or discharge.

The potential of the emitting surface with respect to the metallic cathode carrier and also with respect to a control grid that may be provided, is due to the peculiarity of the heating of the layer very uncertainly defined and may strongly fluctuate from cathode to cathode. Moreover, it must never happen in an amplifier tube with such a cathode that the emission current drops for a prolonged time to zero, for example due to disconnection at a control grid, because the temperature of the cathode would therewith automatically drop and emission would stop. A simple, otherwise customary intensity control by means of a control grid cannot be applied to a tube equipped with such a cathode. The invention accordingly proposes to use in connection with the tube illustrated in the drawing a deflection control for obtaining the distribution control relative to the illustrated remaining electrodes.

The electron beam 5 emanating in operation from the cathode at the surface of the layer 3, which is accelerated in the direction of a first anode '7, is by means of a control electrode 8, which is with respect to the cathode at a negative potential, bundled in such a manner that it enters more or less completely into the aperture of a second anode 9 through which it reaches the collector ltl. As may be readily appreciated, the ratio of the current amounts respectively impacting the second anode 9 and the collector ll can be changed, with the total emission current remaining constant, as is aboslutely necessary for maintaining the emission with the particularly constructed cathode employed. It may be advantageous under certain conditions to arrange and construct the metallic rods operating as auxiliary anode for the firing so that they can be employed for cooperation in the distribution control.

The principle of the thermionic cathode without heater is not inherently limited to the example described herein and illustrated in the drawing.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. A high vacuum amplifier tube having a thermionic cathode, said cathode comprising a conductive cathode carrier, a layer of emission material disposed thereon, and an artifically produced resistance layer disposed between the carrier and the emission layer, said intermediate layer having a resistance which is sufiiciently high that the constant emission current, operating as a transverse current through said resistance layer, is operative as the sole heating means for maintaining the cathode at operating temperature, and at least one auxiliary electrode disposed in engagement with said emission layer, said auxiliary electrode being operative, when positively V biased, to form an auxiliary current path between it and said carrier for the traversing of an initial current operative to initiate emission.

2. A high vacuum amplifier tube according to claim 1, wherein said auxiliary electrode comprises a plurality of rodlike metallic members disposed upon said cathode and uniformly distributed over the surface thereof, and cir- 4s cuit means including a high ohmic resistor for connecting said rodlike members with a positive voltage.

3. A high vacuum amplifier tube according to claim 2, wherein said intermediate resistance layer is made of oxides of earth alkali metals and/ or earth metals.

4. A high vacuum amplifier tube according to claim 2, wherein said intermediate resistance layer is made of substances selected from the class consisting of aluminum oxide magnesium oxide and calcium oxide.

5. A. high vacuum amplifier tube according to claim 2, wherein said intermediate resistance layer consists of high resistance substances forming intermediate layers in customary oxide cathodes.

6. A high vacuum amplifier tube according to claim 2, comprising current distributing control means operating in accordance with the deflection principle.

7. A high vacuum amplifier tube according to claim' 6, wherein said current distributing means comprises a control electrode and at least two subdivided auxiliary anodes.

8. A high vacuum amplifier tube according to claim 6, whereinsaid current distributing means comprises a control electrode and at least two slotted auxiliary anodes.

9. A high vacuum amplifier tube according to claim 6, wherein said auxiliary electrode comprises a part of said current distributing control means.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A HIGH VACUUM AMPLIFIER TUBE HAVING A THERMIONIC CATHODE, SAID CATHODE COMPRISING A CONDUCTIVE CATHODE CARRIER, A LAYER OF EMISSION MATERIAL DISPOSED THEREON, AND AN ARTIFICALLY PRODUCED RESISTANCE LAYER DISPOSED BETWEEN THE CARRIER AND THE EMISSION LAYER, SAID INTERMEDIATE LAYER HAVING A RESISTANCE WHICH IS SUFFICIENTLY HIGH THAT THE CONSTANT EMISSION CURRENT, OPERATING AS A TRANSVERSE CURRENT THROUGH SAID RESISTANCE LAYER, IS OPERATIVE AS THE SOLE HEATING MEANS FOR MAINTAINING THE CATHODE AT OPERATING TEMPERATURE, AND AT LEAST ONE AUXILIARY ELECTRODE DISPOSED IN ENGAGEMENT WITH SAID EMISSION LAYER, SAID AUXILIARY ELECTRODE BEING OPERATIVE, WHEN POSITIVELY BIASED, TO FORM AN AUXILIARY CURRENT PATH BETWEEN IT AND SAID CARRIER FOR THE TRAVERSING OF AN INITIAL CURRENT OPERATIVE TO INITIATE EMISSION.