US2875377A

US2875377A - Electron discharge devices

Info

Publication number: US2875377A
Application number: US616300A
Authority: US
Inventors: Woo Wenfoo George
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1956-10-16
Filing date: 1956-10-16
Publication date: 1959-02-24
Anticipated expiration: 1976-02-24

Description

Feb. 24, 1959 WENFOO GEORGE woo ELECTRON DISCHARGE DEVICES 2 Sheets-Sheet 1 Filed Oct. 16, 1956 Pas/77145 77/524444 I4- cosp/ /c/svr a le's/srxm/cs l 4 hm TIME f STEADV sum;

TIME

/NVEN7'OR WENFOO GEORGE W00 BY @ZM Q Feb. 24, 1959 WENFOO GEORGE woo 2,875,377

ELECTRON DISCHARGE DEVICES Filed Oct. 16, 1956- 2 Sheets-Sheet 2:

/Nl/EN7' O/? WENFOO GEORGE W00 BY M A TTOPNEV nited States Patent ELECTRON DISCHARGE nnvrcns Wen fooGeorge Woo, West Newton, Mass., assignor to Raytheon Manufacturing Company, Walthnm, Mass,

a corporation of Delaware Application October 16, 1956,8erial No. 616,300 Claims. ('Cl. 315-52) is higher than the filament operatingpotential needed forsaid electron discharge device. This combination results in an electron discharge device having a warm-up timethat is kept to a'minimum. In the preferred embodiments, thisinventionhasbeen practiced by construct ing-the defined resistor element in a separate evacuated housing, thereby making an external electrical connection from said resistor to thefilament of said electron discharge device. A second embodiment includes the defined resistor element within the same envelope containing the electron discharge device.

Further objects and advantages of this invention will betmademore apparent by now referring to the accompanying drawings wherein:

Fig. l isa first embodiment of a resistor element constructed in accordance with the teachingsof this invention; "FigLtZ is a graphillustrating the change in heating time as a function of plate: current of an electron'discharge device when utilizing the teachings of this invention;

Fig. 3 is a graph illustrating the effect of different resistances on the efiective operating time as a function of plate current of an electron discharge device;

- Fig. 4 is a schematic diagram illustrating the series connection between the defined resistor and the filament of saidelec'tron' discharge device;

Fig. 5is a graph illustrating the apportionment of the applied voltage between the resistor element and the fila ment of said electron discharge device;

Fig. 6 illustrates the' resistor element illustrated in Fig. l constructed as an integral element within the electron discharge device; and

Fig. 7 is a second embodiment of a second resistor element constructed as an integral elementin an electron discharge device.

Referring now to Fig. 1, there is shown a tungsten resistive element 10 held in thermal contact with a heatabsorbing-mass 11. The heat mass 11 may be, for ex ample, a cylinder of nickel with the tungsten heater element" 10 electrically insulated therefrom by being coated withAl'undum. The Alundum coating increases the heatabsorbing capacity ofthe device and provides good thermalcontactbetween the element Ic and the mass 11.

bya glass envelope. 12, which is, in turn, mounted on a conventional tube socket base 13. In order to achieve long life for element 10, the space within envelope 12 is evacuated and a getter 14 is provided for purging the evacuated chamber of any gases. Mica waferslS support heat mass 11 within envelope getter 14 in a conventional manner that is well known in the tube art. 'Tungsten wire is known to have a low heat capacity and'a high temperature coefiicient of resistance, and hence when tungsten alone'is used as a resistor, the resistance reaches a steady-state value in a traction of a second due to the quick temperature rise of the tungsten. However, by placing heat absorber 11 in. thermal contact with tungsten wire 10, the heat capacity is changed, since the tungsten wire can no longer come up to asteady state of resistance immediately due to the heat-absorbing member 11, which must also be warmed up. It is now resistance by choosing the possible, therefore, to control the rate of change of. resistance by controlling the heat transfer characteristics of said resistor by the proper addition of a heat absorber. The term heat absorber as used herein is synonymous with the term heat sink, and, further, the term thermal contact precludes heating of the heat mass by radiation. The embodiment illustrated in Fig. 1, therefore, allows first,'a control of resistance by selecting, the proper element 10 and, second, a. control over the rate of change of proper heat-absorbing element 11.

Referring now to Fig. 4, there is shown an external resistance 16, illustrated as R and which is similar to that illustrated in Fig. 1, connected in series with the filament 17 of an external tube, illustrated as R The series combination of R and R are connected: across a source of voltage represented as battery 18. In. actual operation, tests were performed with receiving tube type 6AK5, the filament of which is represented as resistor 17 and a supply voltage from source 18 having a value of approximately 8 volts. The filament voltage rating for tube 6AK5 is known to be 6.3 volts from normal operation. In the circuit illustrated in Fig. 4, if the resistanceof resistor 16 and the resistance of filament 17' both have positive temperature coefiicients, and ifrthe R,, is. such that its resistance increases at a slower rate than R then the voltage across R; andthe voltage across R, will reach their steady-state values at difierent rates. Therefore, when the voltage source 18 is applied across the series combination 0th, and RgR will reacha high value quickly while R,, is still low because of its high heat capacity due to. the heat-absorbing mass held in thermal contact with. the resistive elements previously described. The result, therefore, is that the: voltage across filament 171. is higher than normal, while the resistance of resistor 16 is increasing to its normal steady-state resistance. By properly choosing the value of resistor R and the value of the heat-absorbing ni'assheld in thermal contact with.

said resistor, it is possible to'initially supply a higher voltage to the filament of the tube and also control the rate of change of said voltage ash, comes up to final tempera ture. Fig. 2 illustrates a graph of plate current Versus time 'fo'r an idealiz'edset of conditions -for'the warm-up or heati'ngofatube type 6AKS. Current curve 19 shows the, heating rate with the normal 6.3 volts applie'dtothe filament. Curve19 showsthat the normal op era'ting currntfillustratd byreference 20 isreached at a point-cf time represented by 'refetencefl. Curve zz illus't'rate 's the theoretical shortest time available, since an applied 12 and also supportvoltage of"8"volts was applied directly'to the filament of said tube for 7 seconds and then reduced to the filament rating of 6.3 volts. The result of this graph shows that it is theoretically possible to have a tube in an operating condition within 9 to 14 seconds, as compared to curve 19, which took approximately 90 seconds.

In Fig. 3 there is shown a curve 23, which is a normal curve for 6AK5 having, the 6.3 volts applied directly to the filament. Curve 24 illustrates the effect of a series resistor having an overshoot characteristic, whereas curve 25 illustrates a series resistor having an undershoot characteristic. The terms overshoot and undershoot simply refer to the voltage which is applied to the fila ment of the tube under test as a result of the change of resistance in the external resistors. The curve 26 illustrated in Fig. shows the distribution of the applied voltage illustrated in Fig. 4 across the external resistor and the filament 6AK5. It can be seen that, at time zero, due to the external mass in contact with the external resistor, a substantially small portion of the applied voltage develops across the external resistor, or, conversely, a substantially large amount of the applied voltage is directly applied to the filament of the tube, thereby reducing the warm-up time. As current passes through the external resistor, the resistance is allowed by the external mass attached thereto to gradually heat up at a predetermined rate, thereby increasing its resistance and apportionately taking a larger percentage of the applied voltage. This process continues until a substantially steady-state condition is reached, whereby that portion of the voltage developed across the filament circuit of the tube will be approximately the voltage needed for normal continuous operation. It can be seen, therefore, that in practicing this invention it is necessary that the applied voltage always be higher than the normal filament rating of the tube to be controlled.

Referring now to Fig. 6, there is shown within evacuated envelope 27 a complete tube structure 28, such as a 6AK5, in combination with an external resistor 29. The tube structure 28 includes anode .30, filament 31, cathode 32, control grids, not illustrated, and a getter 33. The design of this tube structure would be determined by external characteristics of the circuits in which tubes of these types would operate and, as such, do not form part of this invention except in their defined relation with the resistor now to be described. Upper and lower mica supports 34 and 35 support the defined tube structure in envelope 27. One end of filament 31 is connected to lead .36, whereas the other end of filament'31'is taken from the upper portion of the tube by means of lead 37 to a spring device 38, which is, in turn, attached to upper wafer 34. Spring device 38 has the dual purpose of maintaining tension on lead 37 and providing an upper anchor point for the external resistor 29. Spring device 38 also provides a junction point between lead 37 and one end of resistor wire 29, which is made to extend through an opening in upper wafer 34 and through lower wafer 35 to lead 39 to which the lower end of resistor wire 29 is anchored. In this manner, a series connection exists from leads 39 through resistor wire 29, lead wire 37, filament 31, to lead wire 36, resistor 29 being constructed basically of atungsten wire covered with aluminum oxide, which is a relatively poor heat conductor. The aluminum oxide acts as a heat sink for the tungsten wire, and thus acts as a heat mass for delaying the temperature rise of the tungsten wire. It can be seen, therefore, that, by properly choosing the resistor element and also the proper kind of heat mass as well as the amount of heat mass, complete control over warm-up time can be achieved.

. Referring now to Fig. 7, ,there is shown a complete tube assembly 40 and a resistor element 41, as shown in Fig. 1, completely enclosed in. evacuated housing42. In Fig. 7. the tube-elements and theresistor elements 41' are supported in a conventional manner by means of wafers 43 4 l and 44.- In addition, said wafers also provide the structural support for resistor element 41. The advantage of incorporating the resistor element 41, as constructed in Fig. 1, in the tube itself is having both leads 45 and 46 from said resistor project from below wafer 44, thereby keeping to a minimum the internal changes for the interconnections between lead 45 and filament 47. Lead 48 is connected to one end of filament 47a, whereas lead 49 serves as the connection point for lead 45 from resistor 41 and the other end 47 from filament 47a. The second lead 46 from resistor 41 is, in turn, connected to another lead 50. It will be observed that the structure illustrated in Fig. 7 utilizes an extra lead and pin than is otherwise necessary for the operation of the complete tube. particular mode of construction was chosen to illustrate the various possible types of construction that could be utilized to obtain the necessary structural support'for the internal electrical connections.

This completes the description of the embodiments of the invention illustrated herein. However, many modifications will be apparent to persons skilled in the art, such as the means for anchoring the leads illustrated in Figs. 6 and 7 may be different from that as shown, and,

further, other types of resistor materials may be used incombination with other heat-absorbing masses other than those illustrated in the invention in order to practice the benefits of the invention. It is intended, therefore that this invention not be limited to the details described and illustrated herein, except as defined by the appended claims.

What is claimed is: r 1. In combination, an electron discharge device comprising at least a filament and an anode, a resistor element having a positive coeflicient of resistance with temperature held in thermal contact with a heat absorbing'mass for retarding the temperature rise or said reisstor, an evacuated envelope completely covering said resistor and said heat absorbing mass, said resistor being connected in series with the filament of said electron discharge device, and a source of voltage impressed across said series combination of said resistor and said filament for operating said electron discharge device.

2. In combination, an electron discharge device. comprising at least a filament and an anode, a resistor element having a positive coefficient of resistance with temperature held in thermal contact with a heat absorbing. mass for retarding the temperature rise of said .resistor, and a single evacuated envelope completely enclosing said resistor and said electron discharge device, said resistor being connected in series with said filament within said envelope.

3. In combination, an electron discharge devicecomprisng at least a filament and an anode, a tungsten wire.

resistor element having a positive coefficient of resistance with temperature held in thermal contact with a heat. absorbing mass for retarding the temperature rise of said tungsten wire resistor, and a single evacuated envelope completely enclosing said resistor and said electron discharge device, said resistor and said filament being connected in series within said envelope.

4. In combination, an electron discharge devicec'omprising at least a filament and an anode, aresistor element having a positive coefficient of resistance with temperature held in thermal contact with a heat absorbing, mass for retarding the temperature rise of said resistor, said heat absorbing mass consisting of aluminum oxide held in thermal contact with said resistor, andv an evacuated envelope completely covering said resistor and said heat absorbing mass, said resistor and said filament being connected in series within said envelope. v

5. In combination, an electron discharge device comprising at least a filament and an anode, a resistor element having a positive coefficient of resistance, with temperature held in thermal contactjwith ia;heat absorbingmass for retarding the temperature rise of said resistor, said resistor having a rate of increase of said resistance that is less than the rate of increase of said filament, an evacuated envelope completely covering said resistor and said heat absorbing mass, said resistor being connected in series with the filament of said electron discharge device, and a source of voltage impressed across said series combination of said resistor and said filament for operating said electron discharge device.

References Cited in the tile of this patent UNITED STATES PATENTS Murphy Jan. 15, 1929 Lompe et a1 Sept. 8, 1942 Leuthold Apr. 18, 1944 Seargent Dec. 28, 1948