US2968742A - High efficiency triode vacuum tube - Google Patents

Description

1951 R. c. A. ELAND 68,742

HIGH EFFICIENCY TRIODE VACUUM TUBE Filed July 25, 1958 3 Sheets-Sheet 1 INVENTOR. 1766537 6. ,4- EA 4ND R. C. A. ELAND HIGH EFFICIENCY TRIODE VACUUM TUBE Jan. 17, 19 1 Filed July .25, 1958 3 Sheets-Sheet 2 INVENTOR. 05516, 6. A. [144/0 BY United States Patent 2,968,742 HIGH EFFICIENCY TRIODE VACUUM TUBE Robert C. A. Eland, Arcadia, Caliii, assignor to Standard Coil Products (30., Inc., Melrose Park, 11]., a corporation of Illinois Filed July 25, 1958, Ser. No. 750,956

Claims. (Cl. 313-293) This invention relates generally to triode vacuum tubes, and more particularly relates to novel triode construction that increases its overall gain performance and efiiciency in high frequency amplifier circuits.

Practical and commercial triode vacuum tubes have substantially lower dynamic plate resistances than those of tetrode and pentode vacuum tubes. The addition of the screen grid electrode in tetrode and pentode vacuum tubes substantially increases their dynamic plate resistance so that a typical RF output circuit connected to its output operates at optimum.

The susbtantially large dynamic plate resistance of screen grid tubes does not reduce the efficiency or overall Q of high frequency output circuits.

The dynamic plate resistance of tetrodes and pentodes is of the order of several hundred thousand ohms. On the other hand, the corresponding dynamic plate resistance of triodes is of the order of thousands of ohms in typical constructions, and at best, of the order of tens of thousands of ohms. Thus a highly efiicient or high Q output circuit of a triode RF stage cannot attain optimum performance due to the loading down effect thereon by the internal impedance of the triode tube connected thereacross.

In a given triode tube electrode configuration, the dynamic plate resistance may be increased by reducing the capacity between the plate and control grid electrodes. This correspondingly increases the amplification factor or mu of the triode tube. In tetrodes and pentodes such interelectrode capacity reduction is accomplished by the added screen grid electrode. In cascode circuitry of the type shown in the Nelson Patent 2,775,659, the second triode stage is connected as a grounded grid amplifier to accomplish equivalent results.

In the case of pentode and tetrode tubes, current drawn by the screen grid increases the noise figure of the tube, and accordingly such tubes are inferior to triodes where noise performance is important, as in television reception. In the case of television tuners in VHF range, namely from 54 to 216 megacycles, the high dynamic plate resistance of tetrodes and pentodes cannot all be utilized in the RF stage due to the band width requirements. In the case of a single triode RF amplifier stage, the available dynamic plate resistance in such tubes constructed heretofore is approximately /2 to /3 lower than is requisite for optimum gain performance.

In accordance with the present invention, the capacity between the plate and control grid electrodes of a triode vacuum tube is reduced in a novel manner by a factor of two to three, to one. The dynamic plate resistance of the resultant triode of the invention is thereby made sufficiently high to perform in an amplifier stage to yield an overall gain comparable to that of tetrode, pentode and cascode amplifier stages, i.e. where the transconductance of the tubes is of the same order.

The interelectrode capacitance reduction between the plate and control grid electrodes correspondingly increases the dynamic plate resistance of the triode vacuum tube and renders the overall amplification action of the tube in conjunction with a high efficiency output circuit thereacross more efiicient, as is fully described hereinafter. This advantageous gain is acomplished in the present invention without increasing the noise factor, or degrading other advantageous characteristics of the triode vaccum tube.

As is well known in the art, a triode vacuum tube is essentially a diode to which a third or control electrode is added between the cathode and the plate electrodes for the purpose of controlling the flow of electrons to the plate. The control grid electrode is in the form of a screen or lattice, serving as an imperfect electrostatic shield. The control grid is usually operated at a negative potential with respect to the cathode, thereby controlling the number of electrons that pass between the grid wires on their way to the plate electrode.

Under such negative bias arrangement substantially no grid current flows, and accordingly the amplification by the triode is with relatively low noise figure as compared to any tube with a screen grid electrode. The amount of electrons reaching the plate electrode under usual charge-limited conditions is determined practically by the electrostatic field in the cathode-to-grid space. Once the electrons pass the grid electrode, they travel raoidly to the plate electrode, wherein space-charge effects in the grid-to-plate space may be neglected.

The amplification factor of a triode is designated by the constant mu. Mn is a measure of the relative effectiveness of the grid and plate voltages in introducing electro'tatic fields at the surface of the cathode, and is accordingly a measure of the screening effect of the control grid. The constant mu is determined by the geometrv of the tube construction, and is generally independent of the voltages applied to the grid and the plate electrodes.

The amplification factor depends primarily upon the grid structure and construction, and is increased by whatever causes the grid electrode to more completely shield the cathode from fe plate. Closer spacing of the grid wires, or larger diameter grid wires, accordingly result in a higher mu factor. Also, an increase in the distance between the grid and plate electrodes produces a higher amplification factor mu. For RF amplifiers, commercially available triode vacuum tubes of prior constructions have mu factors ranging from about five to about one hundred.

In accordance with the present invention, I incorporate one or more shielding elements in the vicinity between the control grid structure and the plate electrode. The shielding elements are made independent electrically of the grid and plate electrodes, and arranged in a novel manner to substantially lower the electrostatic control effect that the plate exerts upon the cathode surface, without changing the effect that the grid has at the same point. In other words, a larger change in plate voltage is thereupon required to exert a given electrostatic change at the cathode surface that the same triode requires without such shield elements. The result is a higher amplification factor, or mu, for the tube as will be hereinafter set forth in detail. The dynamic plate resistance of the triode is correspondingly increased by these shield elements.

In accordance with the present invention, the total plate electrode structure is made larger than requisite for conducting the electron current of the triode. The active portion of the plate structure is placed opposite the cathode and control grid electrodes, as heretofore, but with the inactive plate portions extending therefrom. The shield elements are interposed between the grid electrode and the inactive plate portions to electrostatically shield them to accomplish the increased mu and plate resistance referred to above.

Such large plate structure is utilized to provide ruggedness thereto, and prevent microphonics in the triode operation. Further, the larger or heavier plate structure hereof, additionally affords adequate heat radiation to maintain a practical dissipation for the tube in operation. There is no increase in the tub-e volume. The principles of the present invention are applicable to triode structures of various types, configurations, and sizes, as will be here inafter set forth.

The added shield elements within the triode of the present invention increases the electrostatic isolation between the control grid and plate electrodes. This results in a substantially lower amount of oscillator voltage appearing on the grid electrode in a superhe-terodyne tuner incorporating such triode in the input RF amplifier stage. Accordingly, when used in an RF or television tuner, radiation of oscillator signal from the antenna is reduced significantly, particularly at the higher frequencies.

The triode vacuum tube of the present invention is accordingly eminently suited for use in high frequency amplifiers, and in tuner circuitry such as for FM and television receivers in the first RF stage thereof. Its relatively high gain, high efiiciency, and low noise factor makes it superior to pentode and tetrode amplifiers therefore, and comparable to the low noise but more expensive cascode circuitry. Its ruggedness, freedom from microphonics, and ability to handle considerable signal levels, makes it useful for most high gain RF circuits.

It is accordingly a primary object of the present invention to provide a novel triode vacuum tube of substantially increased amplification factor, with corresponding increase of dynamic plate resistance.

Another object of the present invention is to provide a novel triode vacuum tube with electrostatic shielding elements interposed between the control grid and plate electrodes to substantially reduce the interelectrode capacitance therebetween.

A further object of the present invention is to provide a triode vacuum tube having novel internal electrostatic shielding between the control grid and plate electrodes substantially reducing the interelectrode capacitance there between, with corresponding increase in its amplification and plate resistance.

Still another object of the present invention is to provide a novel triode vacuum tube incorporating shielding elements to reduce the electrostatic field between the control grid and plate electrodes reducing the feed-back and the' neutralization requirements for such tube in high frequency amplificationcircuitry.

Still a further object of the present invention is to provide a novel triode vacuum tube which is highly efficient as an RF amplifier stage when connected to a high Q tuned output circuit, with a substantially improved resultant overall amplification.

The above and further objects of the present invention will become more apparent in the following description of exemplary embodiments thereof, taken in conjunction with the drawings, in which:

Figure 1 is a diagrammatic view of one form which the present invention may assume in practice.

Figure 2 is a perspective illustration of the electrode arrangement of the triode vacuum tube of Figure 1.

Figure 3 is an elevational view of a triode vacuum tube corresponding to Figures 1 and 2.

Figure 4 is a schematic electrical diagram of the internal components of the triode of Figures 1, 2 and 3.

Figure 5 is a diagrammatic view of a modified form of triode vacuum tube in accordance with the present invention.

Figure 6 is a partial perspective illustration of the internal components of the triode of Figure 5.

Figure 7 is a further form of a triode electron tube in accordance with my invention.

Figure 8 is an enlarged perspective view showing the internal components of the triode of Figure 7.

Figures 9 through 14 are diagrammatic illustrations of several other forms which the triode of the present invention may assume in practice.

Figure 15 is a schematic electrical diagram of an RF amplifier circuit incorporating a triode vacuum tube of the present invention.

Figure 16 is a diagrammatic representation of the tuned output circuit of the RF amplifier stage of Figure 15.

In Figure l is illustrated one embodiment of a triode vacuum tube incorporating the principles of my invention herein. The triode vacuum tube 20 comprises an evacuated glass envelope 21. Mounted within envelope 21 is a generally cylindrical plate structure 22, a central tubular cathode 23, and a helical grid structure 24 between plate structure 22 and cathode 23. The triode electrodes namely plate 22, cathode 23 and control grid 24, are anchored within the vacuum tube 20 in any suitable well known manner.

The plate structure 22 comprises two active plate elec-' trode surface portions 25, 26 exposed to control grid 24 and cathode 23. The radial distance of active plate surfaces 23, 26 is closer to the cathode 23 than that of the remainder of the plate structure 22. The plate structure 22 is preferably fabricated of two similar semi-cylindrical sections, joined respectively such as by spot welding along seams 27, 28. The shielding elements of triode 23 comprise two metallic cylindrical sections 30, 31 interposed between the inactive plate portions 32, 33 and the control grid electrode 24.

The radial distance of the arcuate cylindrical shield sections 30, 31 is made substantially equal to that of the active plate areas 25, 26. Shields 30, 31 are arranged to constitute an eifective electrostatic shield between the cathode 23 and control grid 24, particularly with respect to the said inactive plate portions 32, 33. Shield elements 30, 31 restrict the electrostatic field between the overall anode structure 22 and the control electrode 24 restricting the beam of electrons from the cathode 23 thereto by directing more of the emitted electrons from the surface of the cathode 23 to the active plate areas 25, 26.

The shields 30, 31 are, in the preferred embodiment, connected to the potential of cathode 23. These shields 30, 31 of course may be connected to signal ground potential, or to other comparable potential levels to effect the purposes of the present invention. The electrostatic shields 30, 31 shield the control grid 24 and its associated supporting members 34, 34 from the inactive portions 32, 33 of the plate structure 22.

Figure 2 is a perspective illustration of the arrangement of the components of the triode 20 illustrated in Figure l. The cylindrical cathode structure 23 is coaxial in the tube 20 and the grid electrode 24 is wound in a helical arrangement about supporting pins 34, 34 (shown in Figure 1). Mounting tabs 35, 35 ext-end from several edge portions of the anode structure 22 for securement with mica supports 36, 37 (Figure 3) within the tube. Similar supporting tabs 38, 38 extend from the shielding plates 30, 31 for mounting in supports 36, 37.

Figure 3 illustrates the mutual supporting arrangement of the electrode components of the vacuum tube hereof within the evacuated glass envelope 21. Details of such arrangement are not shown, as they would be apparent to those skilled in the art. The upper extending tabs 38, 38 of the shielding plates 30, 31 are electrically interconnected by a transverse bar 40 to establish a common potential for the shielding. One of the lower anode tabs 35 is connected by lead 42 to socket pin 41 extending through the evacuated vessel 21. Similarly a lower tab 38 from the shields 30, 31 is connected to a socket pin 43 through lead 44. The grid electrode 24 extends through lead 45 to socket pin 46. The cathode 23 is connected to pin 48 through lead 47. The heater within cathode 23 is connected to pins 49 and 59 through leads 5-1, 52 respectively.

Figure 4 schematically illustrates the aforesaid electrode and shield connections to their respective socket pins. The shield elements 30, 31 are preferably internally interconnected, as through bar 40 (Figure 3) and as indicated by the dotted line 53 in Figure 4.

Further, the interconnected shield elements 30, 31 may be internally connected to the cathode 23, as indicated by the dotted shorting lead 54. This would save the use of socket pin 43, but reduce the circuit flexibility for utilization of the shield elements 30, 31.

As is evident from Figures 1 through 4, an important result of the invention triode arrangement utilizing the electrostatic shielding elements 30, 31 as set forth, is that the electrostatic control effect exerted by the active plate areas 25, 26 at the surface of cathode 23 is lowered without changing the effect that the control grid 24 has at the cathode surface. Thus, a larger change in plate voltage is required to produce the same electrostatic change at the cathode 23 surface as compared to that of the same triode structure without the shields 38, 31.

Mu is by definition dE a-dE with the plate current constant. E and E are the plate and control grid potentials, and 1,, is plate current. Mn is in effect a measure of a small change in plate voltvge required to produce a given electrostatic change at the cathode equal to that of a correspondingly small change in the applied grid voltage, for a constant plate current condition. Mn is the effective amplification factor of the triode tube. However, since the shield elements 30, 31 thereof increases the requisite dE for the reasons stated above, it follows that the mu of the tube 2t) is increased by the electrostatic shields 30, 31.

The plate resistance of a triode vacuum tube is designated by the symbol r,, and is the dynamic plate resistance of an operating triode. The dynfmic plate resistance is a function of the effect of dE, as it relates to its effect on plate current. This relationship is as follows: r =dE +dI However, since more change in the plate potential is required by the tube 28 due to shields 30, 31 to produce the same change in plate current, the dynamic plate resistance r thereof is correspondingly increased thereby.

In practice, it has been found that the dynamic plate resistance r as Well as the amplification factor mu of triodes constructed with the arrangement hereof, incorporating a reduced active plate area (corresponding to 25, 26), and shielding by shield elements (corresponding to 38, 31) of the inactive plate portions (corresponding to 32, 33), have been increased in practice on the order of two to three times over that of unshielded triodes. Such higher gain and plate resistance of the triode is accomplished Without any increase in its noise figure, because no current is drawn through the signalgrounded shield plates 39, 31. Also, by using the invention triode 28 across a tuned RF circuit, overall Q and performance efficiency of the circuit is substantially increased, with a resultant higher RF amplifier stage gain, as is described in connection with Figures 15 and 16 hereinafter.

In view of the active portion of the anode structure 22, namely the areas 25, 26, being a fraction of that of the whole anode structure 22, ruggedness and absence of microphonics is assured in the tube hereof. In other words, by taking advantage of the volume within the cylindrical tube envelope 2f, the anode structure 22 is made substantially larger than the requisite active plate electrode area 25, 26 to impart ruggedness to the anode electrode as mounted between the mica supports 36, 37. The anode structure 22 hereof also affords adequate heat radiation surface for substantial dissipation due to current as the tube is utilized in conventional RF circuits.

For low signal inputs, namely in the microvolt range, microphonics and stability are important factors which are overcome by the invention structure. For high signal inputs, of the order of volts, with relatively heavier plate current necessary, the inactive plate portions or wings 32, 33 provide adequate heat dissipation. Also, a comparatively high value plate current is usually required to give a reasonably good value of transconductance, with higher plate dissipation being used even at low level input signals.

Figures 5 and 6 illustrate a variation of the structural arrangement of the triode electrodes, wherein a basically elliptical conformation is used in contradistinction to the circular arrangement thereof of triode 20 of Figures 1 to 4. The triode 69 comprises evacuated glass envelope 61 within which are suitably mounted an elliptical plate structure 62 having reduced active plate sections 63, 64 radially closer to the central axis of tube 60 than the inactive plate portions 65, 66. The central cathode 67 is generally rectangular in shape, with its wider dimension in line with the longer axis of the elliptical plate structure 62.

The control grid 68 is ellptical in arrangement, conforming with the elliptical plttern of the plate structure 62 as seen in Figures 5 and 6. The supporting pins 69, 69 maintain the grid structure 68 in a helical pattern, seen clearly in Figure 6. The shielding elements 70, 71 of triode 60 are segments of an ellipse, and extend across the inactive plate portions 65, 66 as illustrated. The shields 7 0, 71 are coextensive with the inactive plate portions 65, 66 aforesaid, with their edges extending close to those of active plate portions 63, 64 to constitute an effective electrostatic shield between the control electrode 68 and the inactive plate portions 65, 66 in a manner already set forth in connection with Figures 1 to 4. The improved amplification factor and increased dynamic plate resistance of triode 69 is comparable to that imparted by the shielding elements of tube 20' hereinabove, and for same reasons, as will be understood by those skilled in the art.

Figures 7 and 8 illustrate a further modification of a triode incorporating the invention shielding elements, with increased amplification factor mu and greater dynamic plate resistance afforded thereby, in accordance with the principles of the invention hereof. The triode 75 of Figures 7 and 8 has a generally rectangular plate structure 76 arrangement. The active plate areas 77, 78 are flat surfaces parallel to the rectangular central cathode structure 79. Also, the grid structure of tube 75 is of rectangular construction and incorporates a rigid grid frame support. The active control grid wires 80 are accordingly parallel to the flat active anode surfaces It is to be understood that the anode structure 76 is in a tubular arrangement as illustrated in perspective in Figure 8. It is preferably composed of two similar halfsections, spotwelded or otherwise affixed along their abutting edges 81, 82. The active anode surfaces 77, 78 extend inwardly from the basic anode structure 76, wherein the inactive plate areas 83, 84 are shielded from the control grid 80 and cathode 79 by the shield elements 85, 86. The shield plates 85, 86 are U-shaped, and are coextensive with the inactive plate areas 83, 84. The outer edges of the U-shaped shield members 85, 86 are proportioned to extend close to the edges of active anode areas 77, 78 as illustrated in Figures 7 and 8, to constitute a significant electrostatic shield for the whole of the plate structure 76 with respect to the control grid 80, leaving exposed for action the active anode areas 77, 78 for the reasons set forth in detail hereinabove. The rigid grid support structure for the wound grid 80 comprises end vertical bars 87, 83 joined by cross-bars 89, 90.

Figures 9 through 15 illustrate still further geometric forms 'and arangements which the internally shielded triode vacuum tube of the present invention may assume.

In the triode vacuum tubes of Figures 9 through 14, the assembly is formed in two separated secplate structure tions, which are separately mounted within the vacuum tube assembly and of course electrically interconnected for common anode action, as will be understood. Such plate structure division may be extended to three, four, etc. sections.

In Figure 9, a generally rectangular arrangement for the plate structure 96 of triode 95 is shown similar to that of Figures 7 and 8. The plate structure 96 has opposed active anode areas 97, 98 extending centrally inwardly from the inactive wing portions 99, 100 of the anode structure 96. The plate structures of Figures 9 through 14, as well as the other components of the triodes represented therein, are illustrated in diagrammatic form, and are understood to be longitudinal and tubular in nature, generally corresponding to the corresponding structures depicted, in perspective Figures 2, 6 and 8 hereinabove, and as described in connection with the triodes 20, 60, 75 related thereto.

The separated plate structure 96 is supported by pins indicated at 101, for rigidity of mounting and elimination of microphonics. The central grid structure 102, and internal cathode 103, are parallel to the fiat active anode surfaces 97, 98. The U-shaped electrostatic shields 104, 105 are substantially longitudinally coextensive with the tubular anode structure 96, and arranged to eifectively shield the wing or inactive plate structure portions 99, 100 for reducing the electrostatic and capacitive characteristics of the tube 95 between the grid structure 102 and the plate structure 96. The electrostatic shields 104, are supported by the indicated mounting pins 106,

Figure illustrates triode 110 having arcuate instead of plane wing and shield members. The plate structure 111 thereof comprises fiat central active anode portions 112, 113, with inactive wing portions 114, 115. The central cathode 116 and grid electrode 117 are parallel to the active anode members 112, 113 and coact therewith as a triode amplifier. The semi-circular or arcuate shielding members 118, 119 are coextensive longitudinally with the plate structure 111, and efiectuate the electrostatic shielding and capacitive minimization between the grid structure 117 and the inactive wing portions 114, 115 of the plate assembly 111. Supporting pins 120 for the anode structure 111 and pins 121 for the shielding members 118 and 119 are also provided.

In Figure 11 is illustrated a triode vacuum tube arrangement 125 having two spaced plate anode members constituting plate structure 126. The plate structure 126 comprises central parallel active anode areas 127, 128 with extending plane wing portions 129, 130 which are mactive in the triode electrical operation. The control grid 131 and central cathole 132 are parallel to the active anodes 127, 128. The shield members 133, 134 are V-shaped and are coextensive longitudinally with the anode assembly 126. The shield members 133, 134 are arranged to electrostatically shield the control grid 131 and cathode 132 from the electrically inactive portions of the anode structure 126 which includes the wing sections 129, 130 and the intermediate portions extending outwardly from the active anode plates 127 128. Mountlng rods 135, 136 are indicated for the shield members 133, 134.

In Figure 12, the triode vacuum tube 140 comprises a modified anode structure 141 which includes the flat parallel central anode surfaces 142, 143 coacting with rectangular control grid 144 and central rectangular cathode 145 parallel thereto. The active anode plates 142, 143 are backed up and rigidly supported by T- members comprising outside plates 146, 147 with respective transverse plates 1 18, 149 therebetween, as clearly illustrated. The anode plate structure 141 is understood to be coextensive axially of the active portion of the-vacuum tube elements, which includes the cathode 145 and control electrode 144 longitudinally of the tube 140. The backplates 147, 148 are mounted within the of the plate assembly 141 are electrically interconnected,

and establish a rigid mounting for the active plate areas 142, 143, as well as means for dissipating heat from the active plate areas during operation. I

The inactive portions 146, 147, 148, 149 of plate assembly 141 are electrostatically shielded from the control grid 144 through shield members 151, 152, illustrated as U-shaped. Members 151, 152 are coextensive with the longitudinal extent of the plate assembly 141. The ends of U-members 151, 152 extend close to the edges of the flat anode members 142, 143 to effect the substantial reduction in the capacitance between the control grid 144 and the whole plate assembly 141. The shielding plates 151, 152 are connected to the cathode potential, or signal ground, as set forth hereinabove.

Figure 13 illustrates a form of the invention wherein the triode diagrammatically indicated at contains two opposed rectangular tubular members 161, 162 constituting the plate assembly. The anode members 161, 162 are electrically interconnected (not shown) and comprise active anode surfaces 163, 164 facing each other. It is to be understood that the plate assembly 161, 162 is longitudinal of the tube 160 and with the cathode 165 and control grid 166 constitutes the triode action. The central control grid-cathode assembly 165, 166 is parallel to the active anode plate portions 163, 164. The inactive portions of the plate assembly 161, 162 extend as hollow tubes behind the active anode surfaces 163, 164 to efiectuate rigId mechanical structural mounting, and avoid microphonics. Also, the tubular nature of the anode structure affords ample heat dissipation for the active plate areas 163, 164. p

The U-shaped shield members 167, 168 substantially minimize effective capacitance between the grid structure 166 and the anode structure 161, 162. The U-shaped members 167, 168 have their edges arranged close to the edges of the active plates 163, 164, as shown.

In this manner, the outward inactive portion of the plate structure 161, 162 is shielded from the grid 166 and grid support bars 169, 170. Supporting pins 161 are used to mount shield members 167, 168.

Figure 14 illustrates a form of the invention utilizing rugged active plate members 176, 177 for the triode illustrated diagrarnatically. The active plates 176, 177 are parallel to the central control grid 178 and cathode 179 to constitute a longitudinal triode assembly. The U- shaped shield members 180, 181 extend close to the edges of the respective anode members 176, 177. Electrostatic and capacitive relation between the control grid 178 and particularly of its mounting posts 182, 183 with the anode plates 176, 177 is materially reduced by effecting close spacing of the respective edges of the shields 180, 181 and the adjacent edges of anodes 176, 177.

The electrostatic shielding is thereby maximized with a corresponding minimization of the capacitive value between the control grid structure 17 8 and the plate structure 176, 177, to in turn improve the amplification factor mu and the dynamic plate resistance of the triode 175. The shield members 180, 181 out off the fields of electrostatic force that would otherwise extend from the grid structure 178 including posts 182, 183, to the rear side of the two plane anode plates 176, 177. In this manner, the corresponding capacitance therebetween is minimized to efiect improvement of mu and dynamic plate resistance. The thickness of plates 176, 177 is made sufiicient to resist microphonics and dissipate the heat.

The application of a triode vacuum tube of the present invention in a high frequency RF amplifier stage is. il-

lustrated in Figure 15. The RF amplifier 200 includesv such triode schematically shown at 201. An efficient high Q tuned output circuit is indicated at 202 incorporating a primary winding connected in shunt with a condenser 204, and a secondary output winding 205. The primary Winding 203 connected to the active anodes of 9 tube 201 indicated at 206. The condenser 204 is signal grounded as shown or may be connected to the tube cathode 208. The anode potential is supplied from source B+ to primary 203. Stage 200 may be the first RF amplifier of a VHF television tuner, FM tuner, radar set or other high frequency circuit section.

The control grid 207 is connected to the amplifier input by lead 209. The input circuit 210 comprises primary winding 211 coupled to secondary winding 212 with a tuned condenser 213 in shunt therewith. The output and input circuits 202 and 210 are tuned to the same frequency and band width for the signal amplification desired by stage 200. The tuned input circuit portion 212, 213 is connected to signal grounded, as shown, or to an AGC bias. The cathode 208 is self-biased through resistor 215 shunted by bypass condenser 216. The heater 217 of cathode 208 is suitably connected to a source of supply.

Triode 201 comprises the shield members 220, 221, schematically indicated. It is understood that shield members 220, 221 correspond to those described hereinabove, as for example, shields 30, 31 of triode 20 of Figure 1. Shields 70, 71 of triode 60 of Figure 5, etc. The shields 220, 221 substantially reduces the capacitance between control grid 207 and the plate electrode 206 and substantially increases the mu and the dynamic plate resistance thereof, in the manner and for the reasons described hereinabove. As there is some residual capacitance in the triode 201 between the active portion of plate 206 and grid electrode 207 neutralization is still indicated at high frequencies. Towards this end, a neutralizing capacitor 225 is connected between the low potential point of primary winding 203 and grid electrode 207. The shield members 220, 221 are connected to the cathode 208 potential by respective leads 222 and 223 to point 2 An important advantage of the triodes of my present invention is their substantially higher dynamic plate re sistance as compared to comparable prior art triodes. In this manner, when a tuned circuit is connected to the triode output its efiiciency, its Q is substantially maintained. Figure 16 schematically shows a tuned circuit 230 comprising inductance 231 and condenser 232 in parallel therewith. The conventional measure of the efiiciency of a tuned circuit is designated as Q. The more efficient the higher the Q and the lower the internal resistance therein. Such internal resistance may be represented by a parallel resistance 233 across the tuned circuit 230, significantly higher in value. A high Q tuned circuit has a high impedance. The parallel impedance at resonance W is a resistance 233 equal to wLQ wherein L is the inductance of coil 231. A

Thus when the tuned circuit is connected of a triode, as circuit 202 to plate 206 of tube 201 (Figure 15) the dynamic plate resistance of the triode is in effect also connected across or in parallel with the tuned circuit. This is indicated in Figure 16 by the dynamic plate resistance R in parallel with the equivalent circuit 230 parallel resistance 233. It is thus evident that the higher the value of this added resistance R the higher the composite resistance effective across circuit 230. Thus the more efiicient the tuned circuit and its voltage amplification in the amplifier stage.

to the output The effectively higher dynamic plate resistance of triode 201 in accordance with my invention thus results in a more effective utilization of the tuned circuit 202 in the RF amplifier stage 200. Further, the increased amplification factor or mu in the invention triode 201 additionally improves the signal gain through the amplifier 200. Finally, in view of the reduced capacitance between the plate structure 206 and the control grid electrode 207, any local oscillator or other signal on the output side of the triode 201 results in a correspondingly lower radiation from input side, or extraneous signal 10 level thereof on the heterodyne tuners such as VHF television tuners.

The shield members 220, 221 are at cathode or at signal ground potential and no current is drawn by them. Hence, no internal tube noise is generated due to their presence. The noise factor of the invention triode 201 in a high frequency RF amplifier is the same as that of conventional triodes. The overall resultant gain of the RF amplifier stage 200 is substantially greater than with a conventional triode with the same output circuit 202, being comparable to the gain of tetrode, pentode and cascode stages. The advantage of low noise factor makes it superior than tetrode and pentodes for low level signal inputs, and for television reception; and its lower cost factor makes it more commercial than a cascode stage.

A tube constructed in accordance with the present invention, with the shield members 220, 221 connected to signal ground, compared with a conventional type 6BN4 triode as the input RF stage 200 in a VHF television tuner as follows: The average noise signal produced by the tuner was reduced by 1.5 db with the invention tube over the 6BN4; and the overall gain was doubled at the lower channels, and fifty percent greater at the higher channels. The normal plate voltage for the 6BN4 was volts, and was raised to 200 volts for the invention tube. The invention triode vacuum tube used herein had in one embodiment an amplification factor or mu of 75 dynamic plate resistance of 8,000 ohms at 10 ma. plate current with a transconductance of 9,000 mhos, and a control grid to plate capacitance of .038 [Lllf- Although the present invention has been described in connection with exemplary embodiments thereof, variations and modifications thereof within the broader spirit and scope of the invention will now be apparent to those skilled in the art, and it is not intended to be limited except as set forth in the following claims.

I claim:

1. A vacuum tube operable in the VHF. signal range with dynamic characteristics comparable to a triode comprising a cathode electrode extending longitudinally of the tube, a control grid electrode composed of a wire grid spaced from and substantially surrounding said cathode electrode, a plate structure having an active anode portion supported opposite said wire grid and an inactive plate section extending from each longitudinal edge of said active anode portion, said inactive plate sections being more remotely spaced from the wire grid than the active anode pcrtion spacing, and a shield member interposed between each of said inactive plate sections and said grid electrode, each shield member having an edge region substantially coplanar with said active anode portion and positioned close to a respective longitudinal edge of the active anode portion for effectively inhibiting capacitance between said grid electrode and the inactive plate sections.

2. A vacuum tube as claimed in claim 1, in which said plate structure is tubular in form and contains a second active anode portion supported opposite said wire grid in symmetrical relationship with the first said active anode portion, said inactive plate sections extending to and being joined with said second active anode portion, and said shield members individually extending about said control grid electrode in symmetrical relationship, each of said shield members having second edge regions substantially coplanar with said second active anode portion and positioned close to a respective longitudinal edge thereof.

3. A vacuum tube as claimed total area of said inactive plate sections is substantially greater than the total area of said active anode portions, whereby the effective capacitance between said control gri'd electrode and the plate structure is reduced by a substantial factor by said shield members and the dynamic in claim 2, in which the grid 207. This is important in superplate resistance of the vacuum tube is correspondingly increased.

4. A vacuum tube operable in the V.H.F. signal range with dynamic characteristics comparable to a triode comprising a cathode electrode extending longitudinally of the tube, a control grid electrode composed of a wire grid substantially surrounding said cathode electrode, a plate structure of tubular form surrounding said control grid, said plate structure having at least one planar active anode portion extending integrally therefrom to a position closer to said wire grid than that of residual inactive sections thereof, and shield members interposed between said wire grid and the inactive plate sections, each shield member having an edge region substantially coplanar with said active anode portion and positioned close thereto, said shield members extending about said wire grid to constitute with said active anode portion a tubular array within the tubular plate structure, whereby capacitance between said grid electrode and the plate structure is substantially reduced.

5. A vacuum tube as claimed in claim 4, in which said plate structure contains a second integral planar active anode portion supported opposite said wire grid in symmetrical relationship with the first said active anode portion, said second active anode portion being arranged in the interior tubular array with said shield members and in close proximity therewith.

References Cited in the file of this patent UN1TED STATES PATENTS 2,396,170 Fulton Mar. 5, 1946 2,877,374 Papp Mar. 10, 1959 FOREIGN PATENTS 282,712 Great Britain Mar. 15,1928

OTHER REFERENCES Terman: Radio Engineers Handbook, McGraw-Hill,

20 New York, 1943, pages 301 and 302 relied on.

Notice 01 Aaverse Demsima in Interfereme In Interference No. 91,898 involving Patent Y0. 2,968,742, R. C. A. Eland, Hlgh effimency trlode vacuum tube, final judgment adverse to the patentee was rendered June 24, 1963, as to 012mm 1.

[Ofiioial Gazette Feb many ,4, 1964.]

Disclaimer :2 968-742 R0bert 0. A. Eland, Arcadia, Calif. HIGH EFFICIENCY TRIODE VACUUM TUBE. Patent dated Jan. 17, 1961. Disclaimer filed Feb. 27, 1964:, by the essignee, Standmd Kollsmcm Industm'es Inc. 71 Hereby enters this disclaimer to claim 1 of said patent.

[Ofiicz'al Gazette June 9, 1964.]

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