US2562820A - Electron tube structure - Google Patents

Description

July 31, 1951 J. 2,562,820

ELECTRON TUBE STRUCTURE Filed March 15, 1950 s Sheets-Sheet 2 l a w 1 58 7 l k i g K36 f2? l -12 1 l .95 i J f M21 I .19 L EH2 V I 7)] 58 59 i l l L1 I A h A I l kl l 3! 1 J -7JL I a 7.9 77 a 75 75 a! a? i ooooaoooeoga a I l y 31, 1951 J. D. REID 2,562,820

ELECTRON TUBE STRUCTURE I Filed March 15, 1950 3 Sheets-Sheet 5 I INVENTOR. i I 7 JOHN 0. REID L Q i 822% Q W ATTORNE X Patented July 31, 1951 ELECTRON TUBEIsTRUoTURE I John Drysdale Reid, Cincinnati, Ohio, assignor' to Avco Manufacturing Corporation, Cincinnati, Ohio, a corporation of Delaware 1 Application March 15, 1950, Serial No. 149,836

22 Claims. (Cl. 81558) The present invention relates to a vacuum tube and circuit particularly suitable for operation in; the very high frequency and ultra high frequency ranges.

In designing and operating circuits in the very .1 'high frequency (VHF) and ultra high frequency (UHF) ranges, it has been found that such effects as cathode inductance, grid inductance, input capacitance and circuit connection inductances are sufilciently great so as to produce undesirable or detrimental eifects and various techniques directed to the solution of problems presented by these factors have been developed in the prior art. Tubes have been scaled down to smaller size in order to reduce lead and electrode length, with a resulting decrease in electrode inductance, and capacitance, as well as lead inductance. Also, it has been suggested that leads of relatively large diametershould be employed to reduce lead inductance and skin effect losses.

In view of the increasing commercial importance of the VHF and UHF ranges, it would be desirable to further decrease the loading effect of electrode and lead inductance, thereby increasing the useful frequency range beyond which a resonance effect with inter-electrode capacitance results. It furthermore would be desirable to provide an arrangement wherein the major portion of the circuit is included in the same envelope as a vacuum tube. By providing built-in coupling capacitors it is possible to produce vacuum tubes and circuits having known constants so that reliable operation may be obtained in the UHF ranges.

The present invention minimizes lead loss by including inter-electrode connections in the tube envelope. Electrode inductance is reduced to a minimum in accordance with its teachings by means of a plurality of symmetrical connections to the electrode structures, whereby the signal source effectively sees only one-fourth of the inductive reactance which is seen when conventional connections to the electrode structure are used.

It is, therefore, an object of the present invention to provide an improved vacuum tube construction particularly suited for operation at the higher frequencies.

A further object of the present invention is to provide an improved vacuum tube construction having built-in coupling capacitors.

Another object of theinvention is to provide an improved vacuum tube construction wherein the envelope contain the elements of the thermionic the circuit in which the thermionic tube elements are to operate. 7

A still further. object is to provide an improved vacuum tube construction wherein symmetrical electrode connections are utilized to reduceinherent iru'luctance and.capacitance loading effects of the tube electrodes and connecting leads.

Other and further objects of the present invention subsequently will become apparent by reference to the accompanying drawings, wherein:

Fig. 1 is a diagrammatic view of a tube construction incorporating the principles of the present invention;

Fig. 2 is a base layout showing the symmetrical arrangement desired; a

Fig. 3 is a circuit diagram which is the equivalent of the construction illustrated in Fig. 1;

Figs. 4, 5 and 6 illustrate mixer or converter application circuits embodying the principles of the present invention;

Fig. 7 is a diagrammatic representation illustratingan oscillator tube construction in accordance withv the invention;

Fig. 8 is a diagrammatic representation of a pentode tube construction in accordance with the invention;v

Fig. 9 illustrates a typical base for a vacuum tube constructed in accordance with the Fig. 8

embodiment of the present invention;

Fig. 10 .shows a suitable envelope; Fig. 11 is a simplified end view of the tube structure shown in Fig. 1;

Fig. 12 is an equivalent circuit diagram of the construction illustrated in Fig. 7; and

Fig. 13 shows a simplified schematic diagram .which is the equivalent of the construction shown in Figs. 7 and 12.

Fig. 1, along with end view, Fig. 11, illustrates the construction of a triode suitable for operation as a mixer or converter. The tube has an indirectly heated cathode l2 provided with a connection at each end so as to provide terminals 13 and M. A suitable filament l5 receives curspaced relation to the grid structure I8 there is an anode l9.

Two connections 2| and 22 are provided for the anode l9.

The ends ofthe grid l8 are connected to inductors 23 and 24 which are connected to capacitor sleeves 25 and 26, respectively. The capacitor, sleeves 25 and 26 constitute relatively short cylinders surrounding a portion of the indirectly heatedcathode l2. Each of the cylinders .nection. cathode inductance is also, lowered proportion- .ately by similar construction.

The degenerative effect on the input signal is 25 and 26 is separated from direct contact with the cathode |2 by a suitable insulating sleeve (such as the air gaps shown) which preferably has such qualities as to provide a high resistance leakage path. Thus, a grid leak resistor is provided in parallel with a capacitor formed by each of the cylinders 25 and 26, the leakage of the air dielectric being equivalent to the parameters 20, 30 in Fig. 3.

Surroundin the anode I9 is another cylinder 21, which is electrically connected to the cathode l2, thereby to produce a capacitor 21 between the anode I9 and the cathode I2.

Each end of the cathode I2 is connected to an inductor. Thus, one end of the cathode I2 is connected to an inductor 28, which has its other end connected to a terminal 29. The inductor 28 is inductively coupled to the inductor 23, which is connected to the grid I8. At the other end of the tube structure an inductor 3| is connected to the cathode I2 and to a terminal 32. The inductor 3| is inductively coupled to the inductor 24, which is connected to the grid l8.

In order to understand the principles involved in the tube construction as described above, some of the effects that the leads and electrodes of a conventional tube have on a (UHF) signal must be considered. The conventional cathode and cathode return lead inductances carry both the plate current and any grid-cathode current flowing from the input signal source. Therefore, the voltage drop caused by anode current flowing through the cathode inductance has a degenerative efiect, on the input signal.

some proportion related to the frequency of the applied current. Also, it is well known that an increase in lead length increases the inductive reactance which the lead offers to UHF currents. Therefore, it can be seen, when the grid cathode circuit of a conventional tube is analyzed with a view to using the tube in UHF work, that the physical lengths of the grid structure and the cathode structure are important factors to be considered. In conventional tube constructions, a lead from a base pin is connected to one end of the grid. Also, a similar lead is connected to one end of the cathode structure. This means that the full physical lengths of the grid structure and cathode structure, as well as the lengths of their respective leads, must be considered in determining the inherent inductive reactance of the tubes internal grid-cathode path. The present invention effectively lowers the inductance ,oifered by the tube electrodes, by bringing in leads to both ends of the grid and to both ends of the cathode. Since the circuit is symmetrical,

each input lead to the grid carries one half of the signal current realized in the grid cathode circuit and the inherent inductance of the grid wire is effectively broken into two parallel paths. Each path has an inductance equal to one half of the inductance of the whole grid and since the paths are effectively connected in parallel, the inductive reactance of the grid is reduced to 25% of the inductance of a conventionally connected grid. In other words, a conventional connection, i. e. to one end of the grid, results in a grid inductance four times as large as that produced by the above described double end con- It can now readily be seen that the further reduced by taking the anode return current through two paths i. e. the two leads connected to terminals l3 and I4, directly to both ends of the cathode structure I2, thus reducing to a minimum the cathode circuit inductance common to the grid and plate circuits.

It will become apparent to those skilled in the art that the structure represented in Fig. 1 may be enclosed within a relatively compact envelope and that for the purpose of symmetry and minimum inductive effects, the leads from the various inductors and tube elements preferably are arranged as illustrated in Fig. 2.

Fig. 3 shows the equivalent circuit diagram wherein it will be recalled that imperfect insulation provides a grid leak 20 in parallel with a capacitor 25 and a grid leak 30 in parallel with a capacitor 26. The inductive reactance of the control circuit input leads is also greatly reduced by the construction shown in Fig. 1.

As is stated above, the inductance of a lead increases as its length is increased. In order to keep these leads as short as possible, thereby keeping their inductive reactance as low as possible, inductors 23 and 24 are connected directly between the grid l8 and the capacitance sleeves 25 and 25, inside of the envelope. The illustrated symmetrical construction places these inductors effectively in parallel, thereby making their combined inductance equal to one half of the inductance of a single path. The dual connections to the cathode reduce the cathode structure in- 28 and 3| is connected to the cathode which is connected through an inductor 34 to ground. The inductor 34 is coupled to another inductor 35 which is connected to a suitable source of oscillations which are to be mixed with the incoming energy from the transmission line 33. Since the grid circuit inductors 23 and 24 are in parallel, the total inductance connected between the grid and capacitors 25-28 is only half as much as the inductance of each single inductor and this has been represented as a single inductance in Fig. 4. Likewise, the capacitors 25 and 28 and the accompanying grid resistors may be represented by a single capacitor and grid resistor.

Fig. 5 illustrates the manner in which the structure illustrated in Figs. 1, 2 and 3 may be employed with an unbalanced input wherein one of the conductors of the transmission line 33 is connected to both inductors 28 and 3|, and the other conductor of the transmission line 33 is connected to the common juncture of the inductors 28 and 3|. A suitable tuning capacitor 36 may be connected across the line 33 to provide for variable tuning of the input circuit. The anode IQ of the vacuum tube is coupled through a .capacitor 31 to a suitable source of oscillations.

The anode I9 is connected through the primary winding 38 of an intermediate frequency transformer to a suitable source of anode potential 5. suit of this internaI connection the RF and'osciL- lator frequencies have a low impedance cathode return path which is relatively independent of the impedance of the IF output leads connected between plate I9 and terminals 2| and 22.

Fig. 6 shows still another arrangement wherein the anode l9 is connected directly to the anode 4| of a triode vacuum tube having a grid 42 and a cathode 43. The anodes l9 and 4| of the two vacuum tubes are connected together and through the primary winding 38 of the first intermediate frequency transformer to the terminal 39, which is connected to the source of anode voltage. The grid 42 is connected to ground through grid capacitor 44 wich is shunted by a grid resistor 45. The groimded sides of resistor 45 and capacitor 44 are also connected to one end of an inductance 46 having an intermediate point connected to the cathode 43. The other end of the inductor 46 is connected through a capacitor 98 to the anode 4|.

Referring to Fig. '7 a vacuum tube construction and circuit is illustrated, which is particularly adapted for oscillator use. The cathode is indirectly heated by a suitable filament having electrical terminals 52 and 53. Each end of the cathode 5! is also provided with terminals 54 and 55. At one end of the cathode 5| there is provided an inductor 56 connected thereto, which is also connected to an external terminal 51. At the other end of the cathode 5| there is a similar inductor 58 connected to the cathode and to an external connection or terminal 59.

Inductor 56 is coupled to an inductor 6| connected between the grid structure 62 and cylinder 63. The cylinder 63 surrounds the anode 64 so as to provide a capacitor between the grid 62 and the anode 64. Grid leak resistor 99 is connected between the cylinder 63 and the cathode 5|, thereby furnishing a D. C. path between the said grid and cathode. The anode 64 receives potential through a resistor 65 connected to a terminal 66. At the other end of the grid 62 there is another inductor 61 which is also connected to the cylinder 63. It will be noted that each end of the anode 64 as at 68 and 69, is of smaller diameter so as to be closer to the cathode 5| and the inductors 6| and 61. This produces an increased capacitive eifect at these points. The structure shown in Fig. 7 is one form of a Colpitts oscillator, as can readily be seen by reference to the simplified circuit diagrams of Figs. 12 and 13. The increased capacitive effect realized by decreasing the end diameter of anode 64 at 68 and 69, in Fig. 7, is diagrammatically shown by capacitors 68C and 69C in Fig. 12. Capacitors (390, Fig. 12, includes the inherent grid cathode capacitance between the grid and cathode structures.

In Fig. 13 the circuit of Fig. '7 and Fig. 12 has been further simplified into a more easily recognizable Colpitts circuit. Capacitor Csc illustrates the shield cathode capacitance, while capacitor Cgc illustrates the grid cathode capacitance.

Since the Colpitts circuit is conventional and well known, an exhaustive explanation is not required. However, briefly referring to Fig. 13, it can be seen that coils til-61 and capacitors Cs: and Cgc form a resonant circuit. The voltage across the resonant circuit is divided into two parts by the series circuit comprising condensers Gel: and Cgc. The cathode 5| is effectively coupled to the common connection between these capacitors. Therefore, the instantaneous voltages at the two ends of the resonant circuit are #5 6'. opposite ln'polarity with respect to the cathode and in the right phase relation to sustain oscillations.

Fig. 8 shows the principles of the present invention, applied to a pentode amplifier. An indirectly heated cathode H is provided with connections at each end 12 and 13. The cathode H is heated by a filament energized through connections l4 and 15. The cathode is surrounded by a grid 16 which is connected at each end thereof to an inductor 11 and an inductor I8. Inductor I1 is connected to a capacitor sleeve 19 surrounding a :portion of the cathode H. In a similar manner, the other inductor 18 is connected to a capacitor sleeve 8|, surrounding a portion of cathode H. Capacitor sleeve 8| is connected through blocking resistor I82 to terminal I08, thereby adapting the grid of the amplifier for connection to a D. C. grid bias source. The inductor 18 is effectively coupled to another inductor 82, connected between the cathode II and the terminal 83. In a similar manner, the inductor 11' is coupled to an inductor 84 connected between the cathode l I and a terminal 85.

Just beyond the grid 16 is a screen grid 86 which is connected to a, terminal 81 through a blocking resistor ltll. One end of the screen grid 86 is connected to a capacitor coupling sleeve 88, whereas the other end of the screen grid 86 is-connected to a capacitor coupling sleeve 89. Thus, a certain by-pass capacitance exists between the screen grid 86 and the cathode 1|.

Just beyond the screen grid 86, there is a suppressor grid 9|, which at each end is connected to the cathode II. Beyond the suppressor grid 9| there is located an anode 92, which is connected to a terminal 93. It is to be noted that a D. C. path is not provided through the dielecover the cathode surface directly beneath the control grid structure. The ends of the cathode,

which act as a condenser plate for condensers 25 and 26 in Fig. land for condensers 19, 8| 88 and 89 in Fig.8, are uncoated.

The various terminals for the pentode, vacuum tube and circuit illustrated in Fig. 8 are shown in Fig. 9. The elements of the vacuum tube and circuits may be enclosed in an envelope generally having the appearance illustrated in Fig. 10.

It is to be noted that the longitudinal axes of the internal tube structure is parallel to the base plane surface in lieu of being perpendicular thereto as in a conventional tube. This construction allows the leads extending to the exterior to be of equal length.

From the foregoing embodiments it will be appreciated that the principles of the present invention ofier numerous advantages over arrangements in the prior art. In the mixer or converter application, as shown in Figs. 6 and 5, the oscillator voltage is supplied by coupling or directly connectin the oscillator source to the plate circuit. The capacity existing between the grid and plate, transfers this energy to the grid circuit. It will be appreciated that where, as

in the structure indicated, the input capacitance is low, a large voltage will appear on the grid. Furthermore, if the mutual conductance is high,

anyplate variations will have no substantial detrimental effect.

"In constructing such an arrangement as that suggested by the embodiment described in connection with Fig. l, the capacitances provided by the capacitors 25 and 26 would each be about ten times the usual input capacitance of the tube structure. It will be recalled that the dielectric sleeves which separate the cylinders 25 and 26 from the cathode, were selected so as to be imperfect insulators so that grid leak values of about one megohm could be obtained. The capacitance provided by the capacitor 21 should be large enough to provide a comparatively low impedance at signal frequencies. This capacitance would have a value approximately equal to ten times the capacitance existing between the grid and the plate. It will be recalled that the cylinder 21 which forms one plate of the capacitance also serves as a shield for the plate 19, thus to reduce any oscillator radiation.

While for the purpose of describing and illustrating the drawings, certain embodiments have been specifically shown in the drawings and it is to be understood that the invention is not to be limited thereby, since such variations and other embodiments are contemplated as may be commensurate with the spirit and scope of the invention as defined by the accompanying claims.

I claim:

1. A vacuum tube for a symmetrical circuit comprising a cathode, a concentric grid and a concentric anode, symmetrically arranged inductive elements located between each end of said grid and said cathode, and symmetrically arranged inductive elements located adjacent said first inductive elements and provided with connections extending to the exterior of said vacuum tube.

2. The combination comprising an evacuated envelope containing an indirectly heated cathode, concentric grid and anode structures, symmetrically arranged inductive elements located between each end of said grid and of said cathode and connected in circuit with said tube elements,

symmetrically arranged inductive elements located adjacent said first inductive elements provided with connections extending to the exterior of said envelope and symmetrically arranged connections extending from said cathode, said grid and said anode to the exterior of said envelope.

3. The combination comprising an evacuated envelope containing an indirectly heated cathode, concentric grid and anode structures, a plurality of capacitors each comprising an insulated metal sleeve surrounding said cathode, symmetrically arranged inductive elements located at each end of said grid and connected between said grid and said capacitors and symmetrically arranged inductive elements located adjacent said first inductive elements and provided with connections extending to the exterior of said envelope.

4. The combination comprising an evacuated envelope containing an indirectly heated cathode, concentric grid and anode structures, a plurality of capacitors each comprising an insulated conductive sleeve surrounding said cathode, symmetrically arranged inductive elements located at each end of said grid and connected between said grid and said capacitors and symmetrically arranged inductive elements located adjacent first inductive elements, each of said elements being connected between said cathode and the exterior of said envelope.

5. The combination comprising an evacuated cluding an indirectly heated cathode, having con- 8 4 centric grid and anode structures, symmetrically arranged inductive elements located at each end of said grid and capacitively coupled to one of said thermionic tube elements and symmetrically arranged inductive elements coupled to said first element and connected between said cathode and the exterior of said envelope.

6. A converter and circuit comprising an evacuated envelope containing thermionic tube elements including an indirectly heated cathode having a concentric grid and anode, symmetrically arranged inductive elements located at each end of said grid, a plurality of cylindrical sleeves surrounding said cathode adjacent each end and separated therefrom by a high resistance dielec tric material, said inductive elements being connected between said grid and said cylindrical sleeves and symmetrically arranged inductive elements coupled to said first elements and connected between said cathode and the exterior of said envelope.

7. The combination comprising an evacuated envelope containing thermionic tube elements including an indirectly heated cathode having concentric grid and anode structures, a concentric sleeve surrounding said anode, a plurality of inductances each connected between an end of said grid and said sleeve, a plurality of inductances coupled to said first inductances and connected between said cathode and the exterior of said envelope, said anode having end structures of smaller diameter to provide capacitive coupling between said anode and said cathode and symmetrically arranged connections from said cathode to the exterior of said envelope.

8. The combination comprising an evacuated envelope containing thermionic tube elements including an indirectly heated cathode having concentric grid and anode structures, a plurality of metal sleeves symmetrically arranged adjacent the ends of said cathode and insulated therefrom, a plurality of inductances each connected between an end of said grid and one of said sleeves, a plurality of inductance coupled to said first inductances and connected between said cathode and the exterior of said envelope and symmetrically arranged connections from said cathode to the exterior of said envelope.

9. The combination comprising an evacuated envelope containing thermionic tube elements including an indirectly heated cathode provided with concentric grid and anode structures, one of said grid structures being a screen grid, a plurality of metal sleeves symmetrically arranged adjacent the ends of said cathode and insulated therefrom, a plurality of inductances each connected between an end of the control grid and one of said sleeves and connections between said screen grid and certain of said sleeves, a plurality of inductances coupled to said first inductances and connected between said cathode and the exterior of said envelope and symmetrically arranged connections from said cathode to the exterior of said envelope.

10. The combination comprising an evacuated envelope containing thermionic tube elements including an indirectly heated coated cathode having concentric control. screen and suppressor grid structures, a concentric anode therefor, a plurality of metal sleeves symmetrically arranged adjacent the uncoated ends of said cathode and insulated therefrom, said screen grid bein connected at its ends to certain of said sleeves, said suppressor grid being connected at its ends to 76 symmetrical points on said cathode, a plurality of inductances connected between each end of the control grid and one of said sleeves, a plurality of inductances coupled to said first inductances and connected between said cathode and the exterior of said envelope and symmetrically arranged connections from said cathode to the exterior of said envelope.

11. An electron tube comprising a control electrode and a cathode electrode input circuit, an output circuit including an anode, separate symmetrical built-in connections to both ends of one of said input circuit electrodes, an envelope for containing said electrodes and said built-in connections and signal supplying means coupled to said built-in connections for supplying an input signal between both of said symmetrical built-in connections and the other input circuit electrode, whereby said symmetrical built-in connections afford substantially identical impedance paths from each end of said one electrode to one side of said signal supplying means.

12. An electron tube comprising a control electrode and a cathode electrode input circuit, an output circuit including an anode, first separate symmetrical built-in connections to both ends of said control electrode, second symmetrical builtin connections to both ends of said cathode electrode, an envelope for containing said electrodes and said built-in connections and signal supplying means coupled between said first and second built-in connections whereby said symmetrical built-in connections afiord substantially identical impedance paths from each end of said control electrode to one side of said signal supplying means and also aiford substantially identical impedance paths from each end of said cathode electrode to the other side of said signal supplying means.

13. In a vacuum tube structure the combination comprising an anode, a control grid and a cathode sleeve covered with an electron emissive coating having an uncoated end portion, a builtin capacitor comprising a concentric jacket spaced from said portion by a dielectric and a highly evacuated envelope for containing said anode, cathode, control grid and built-in capacitor.

14. An electron tube comprising an internal tube structure contained in an evacuated envelope which includes a plurality of tubular shaped electrodes in concentric spaced relationship, connections between at least two of the said tubular electrodes and the exterior of the envelope, at least one helical grid structure between two of said electrodes and in concentric spaced relation therewith, a first two terminal inductive means having one terminal connected to one end of said grid structure, a second two terminal inductive means having one terminal connected to the other end of said grid structure, means for coupling the second terminals of the first and second inductive means to opposite ends of one of said plurality of tubular shaped electrodes, a third inductive means located adjacent and inductively coupled to said first said inductive means and a fourth inductive means located adjacent and inductively coupled to said second inductive means, said third and fourth inductive means being provided with connections extending to the exterior of said vacuum tube.

15. An electron tube structure as defined in claim 14 wherein the longitudinal axes of the said tubular shaped electrodes and helical grid structure is parallel to the plane surface of the tube base.

16. An electron tube structure as defined in claim 15 wherein the said means for coupling the second terminals of the first and second inductive means to opposite ends of one of said plurality of tubular shaped electrodes includes a pair of tubular sleeves each in concentric spaced relationship with an uncoated end portion of a partially coated cathode and separated therefrom by a high resistance dielectric.

17. An electron tube structure as defined in claim 15 wherein the said means for coupling the second terminal of the first and second inductive means to opposite ends of one of said plurality of tubular shaped electrodes comprises symmetrical connections to each end of an outer capacitor sleeve surrounding the anode structure.

18. An electron tube internal structure as defined in claim 15 wherein the said connections between at least two of the said tubular electrodes and the exterior of said envelope comprise connections to the cathode and anode electrodes.

19. An electron tube internal structure as defined in claim 18 wherein the said connections to the cathode comprise two symmetrical leads each connected to opposite ends of the said cathode structure.

20. An internal electron tube structure as defined in claim 18 wherein the said connections to the anode comprise two symmetrical leads each connected to opposite ends of the said anode structure.

21. In a vacuum tube structure of the type which includes at least an anode, a control grid and a cathode, a built-in capacitor comprising a cathode element having an uncoated end portion and a concentric jacket spaced from said portion by a dielectric having a high resistance leakage path, whereby there is both an A. C. path and a D. C. path between said cathode sleeve and said concentric jacket.

22. In a vacuum tube structure of the type which includes at least an anode, a control grid and a cathode, the combination comprising a cathode structure, a concentric anode structure spaced from said cathode and an encircling concentric capacitor sleeve spaced from said anode and having a plurality of symmetrical connections between the ends of said cathode and the ends of said capacitor sleeve.

JOHN DRYSDALE REID.

REFERENCES CITED The following references are of record in the

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