US2885642A - Coaxial line vacuum tube circuit - Google Patents

Description

May 5, 1959 L. L. KOROS ET AL 2,885,642

COAXIAL LINE VACUUM TUBE CIRCUIT Filed May 21, 19

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4 Claims. (Cl. 333-82) This invention relates to coaxial line vacuum tube circuits,- and more particularly to a coaxial line circuit coupled to two electrodes of a vacuum tube for use as a tunable input circuit or output circuit. I

A principal objectof this invention is to prov1de a coaxial line vacuum tube circuit characterized in having improved electrical and constructional features over what has been previously known in the .art.

Another object of this invention is to provide an improved coaxial line vacuum tube circuit especially suitable for use over a broad range of operating frequencies.

A further object of this invention is to provide an improved coaxial line vacuum tube circuit especially suitable for handling signals having a relatively broad bandwidth.

A still further object of this invention is to provide an improved coaxial line vacuum tube input circuit for use in a power amplifier stage of a television transmitter to provide a high power output of television signals in the ultra-high frequency range.

A-still further object is to provide an improved input circuit for the power amplifier stage of an ultra-high frequency television broadcasting transmitter which is characterized by electrical properties making it suitable for the amplification of both black and white television signals and color television signals.

In one aspect, the invention comprises a vacuum tube having inner and outer concentric electrode contact-rings one of which is contacted by an outer conductor of a coaxial line, and the-other of which is contacted bythe inner conductor of the coaxial line. The inner conductor consists of two portions which are separated by a dielectric material to constitute a direct current blocking capacitor. A generally annular conductive member is disposed between the outer and inner conductors of the coaxial line, and is axially movable while maintaining electrical contact with the-inner conductor. The effective length of the coaxial line from; the vacuum tube is determined by an annular shorting plunger between the inner and outer conductors. Both the annular conductive member and the annular shorting plunger are axially adjustab-le in position for tuning purposes. A second coaxial line arranged at right angles with the first provides a coupling to the space between the outer and inner conductors of the first coaxial line intermediate the annular conductive member and the annular shorting plunger.

According to a feature of the invention, the end of the inner conductor coupled to the electrode contact ring is flared and provided with a coaxial shoulder. The annular conductive member makes sliding contact at one end with the shoulder, and makes sliding contact at the other end with the body of the inner conductor.

Another feature of the invention is the arrangement whereby the two portions of the inner conductor are provided with mating tapers, and the dielectric material therebetween is in the form of a frusto-conical shell.

A further feature of the invention is the use of a 2,885,642 Patented May 5, 1959 plurality of arcuate members between the outer and inner conductors intermediate the vacuum tube and the annular conductive member. These arcuate members are radially adjustable in position to compensate for departures in the tube and/or in the coaxial line from perfect symmetry.

These and other objects and aspects of the invention will be apparent to those skilled in the art from the following more detailed description, taken in conjunction with the appended drawing, wherein:

Figure 1 is a sectional view of a vacuum tube circuit constructed according to the teachings of this invention;

Figure 2 is a sectional view taken on the line 22 of Figure 1; and

Figure 3 is a sectional view taken on the line 3--3 of Figure 1.

Referring to the drawing, a vacuum tube 10 (shown in part) includes a cathode electrode contact ring 11 and a grid electrode contact ring 12 separated by a dielectric material 13. A coaxial line circuit for the vacuum tube includes an outer conductor 14 and an inner conductor 15. The outer conductor 14 is provided with two longitudinally extending slots 16 and 17. One end of the outer conductor 14 is provided with a flange 18 which is secured in electrical contact with the cathode contact ring 11 of the vacuum tube 10. The other end of the outer conductor 14 is open.

The inner conductor 15 consists of two conductive portions 20 and 21 provided with mating tapers. A frusto-conical dielectric shell 22 is disposed between the mating tapers of the portions 20 and 21 of the inner conductor 15. The dielectric shell 22 cooperates with the tapers to provide a direct current blocking capacitor. By suitable forces acting on the flanges on the portions 20 and 21, the portions are urged together against the dielectric shell 22 with considerable force to positively exclude air pockets which would result in arcing and deterioration of dielectric shell 22. Bolts-23 of insulating material may be used to hold the flanges together.

The end of conductive portion 20 of the inner conductor 15 adjacent to the vacuum tube 10 is flared or radially extended and provided with a coaxial cylindrical shoulder 25. Spring contact fingers on the shoulder 25 engage the grid contact ring 12 of the vacuum tube 10 to permit the removal of the vacuum tube from the coaxial line circuit.

An annular conductive member 27 is disposed coaxially between the outer conductor 14 and the portion 20 of the inner conductor 15, and is provided at one end with spring contact fingers which engage the: shoulder 25, and is provided at the other end with spring fingers which engage the portion 20 of the inner conductor 15. Insulating blocks 28 and 29 extending thru the slots 16 and 17 in the outer conductor 14 are secured at one end to the annular conductive member 27 and at the other end to gear racks 30 and 31, respectively. The gear racks 30 and 31 are external of the outer conductor 14 and are meshed with pinions 32 and 33, respectively. By means of a gear mechanism generally designated 34, coupled to the pinions 32 and 33, the annular conductive member 27 may be axially adjusted in position by means of a knob 35. 4

An adjustable annular shorting plunger 38 provides a short circuit for radio frequencies between the outer conductor 14 and the portion 21 of the inner conductor 15. The shorting plunger 38 may provide a direct current connection between the outer and inner conductors as shown, or may include conductive members contacting the outer and inner conductors and separated by-a dielectric material to constitute a radio frequency bypass assume condenser. The shorting plunger 38 is axially adjustable inposition by 'means of a rack" and pinion mechanism generally designated 39 which is operated by a knob 40.

Radio frequency energy is coupled to and from the cavity 41 by means of a coaxial line including an outer conductor 42 and an inner conductor '43, and a second coaxial line including an'outer conductor 44 andan inner conductor 45; The outer conductors 42 and 44 are secured'to the edges of apertures in' the outer conductor 14 of the coaxial line circuit. The inner conductors 43 and 45- extend intothe'cavity 41 and are provided with terminal capacitor discs 46 and 47. This arrangement provides capacitive coupling; The coupling, if desired, may alternatively include inductivecoupling loops, or direct connections from the inner conductors-43' and 45 to the portion 21 of the'innerconductor 15.

An arcuate member 50 is positioned adjacent to the vacuum tubebetween the-outerconductor14 and the shoulder 25 of the inner conductor bymeans of a support 51 slidably mounted in aslot-SZ in the shoulder 18 of the outer conductor 14. The radial position'of the arcuate member 50"is=adjustable= by means ofsetscrews 53-operating to define the position of the support 51 in the slot 52. Additional arcuate members 55, 56, and 57 are similarly mounted and arranged substantially in a circle withthe'arcuate member 50. The-arcuate mem? bers are. preferably made of electrically conductive material, but may be made of'dielectric material.

In the operation of thecoaxial line vacuum tube circuit as an input circuit of. a power amplifying stage of a television transmitter, radiofrequency-energy to be amplified is applied to the coaxial lineinput circuit thru the coaxial line 42, 43. The coaxial line 44', 45 is connected to an external swamping or broadbanding resistor (not shown).

The annular conductive member 27 isselected to have an axial length inthe order of a quarter wavelength at the desired operatingfrequency. The .lengthof member 27 differs from a quarter wavelength by'an amount introducing a reactance to compensate for the input reactance of tube 10. Various annular conductive members 27 of different axial lengths may be provided for insertion into the coaxial line cavity for operation at any one of many different frequencies within a range such as the range of the ultra-high frequency television band, extending from 470 to 940 megacycles. The positions of the'shorting plunger 38 and the annular conductive member 27 are adjusted so asrto compensate for the internal reactance of the vacuum tube, and so that the distance from the grid inv the tube to the shorting plunger 38 is electrically three-quarters of a wavelength at the operating frequency. The coaxial line circuit is especially useful as an input circuit for a vacuum tube with inductive input reactance. The annular conductive member-27' together with, the outer conductor. 14 form a transmission line section having capacitive reactance which compensates the inductive reactance of the tube.

The dimensions of the coaxial; line circuit including outer conductor 14 and inner conductor 15 are selected to handle radio frequency energy in the coaxial line or TEM' mode. If there is the slightest deviation from perfect symmetry in the vacuum tube 10 or in the coaxial line circuit, the radio frequency energy may be translated, at some frequencies, to an undesired circumferential or TE mode. Energy, which is in the undesired mode is dissipated in the form of heat and detracts from the useful energy which is in the TEM mode. The undesired mode excites the plate current of the tube in a push-pull fashion. However, the output circuit of the tube (not shown) will normally be unable to couple push-pull currents; Therefore, thepush-pullcurrents in the undesired mode cannot serve a useful purpose, and do reduce the useful output power;

In order to prevent the occurrence of oscillations in the circumferential mode, a compensation ismade for the lack of perfect symmetry by introducing a compensating dis-symmetry. The compensating dis-symmetry is accomplished by means of the arcuate members 50, 55, 56, and 57. These arcuate members are individually adjusted in radial position until the circumferential mode is suppressed, and all of the energy is kept in the useful TEM mode.

It is apparentth'atv according to.-this invention there is provideda coaxialline vacuum tube circuit which is useful' over a verywide range of ultra-high frequencies to handle relatively broad-bandsignals having a bandwidth such as 12 megacycles, that the circuit includes novel means to prevent the occurrence of the unwanted wasteful circumferential'mode of oscillation, and that .the construction includes many advantageous features of great practical importance.

What is claimed is:

l. A circuit for, avacuumltube, havinginner and outer electrode contact rings, said circuit comprising a tubular outer conductor adapted at one end to contact said outer ring, a coaxial inner conductor, adapted at one end'to contact said inner ring, said inner conductor including two metallic portions separated by dielectric material to form a direct current blocking capacitor, ,said inner conductor being extended radially outwardly adjacent said one end thereof to provide a coaxial shoulder; an annular entirely metallic member having an electrical axiallength on the order of a quarter-wavelength at the operating frequency such as to provide a reactance compensating the reactance of said tube, said member being mounted between said outer and inner conductors, closely adjacent the tube end of said inner conductor, and having sliding electrical contact at its ends. with only 'saidinner conductor, with one end of said member engaging said shoulder on said inner conductor; means to axially adjust the position of said'member, an annular adjustable shorting plunger between said 'outerand inner conductors at the other ends thereof, and an energy transferring coaxial line extending at right angles to said outer and inner conductors at a location intermediate said member and said plunger, the inner conductor of said coaxial line extending into the space between said inner and outer conductors;

2. A circuit for a vacuum'tube having inner and outer electrode contact rings, said circuit comprising a tubular outer conductor adapted at one end tocontact said outer ring, a coaxial inner conductor adapted at one end to contact said inner ring, said inner conductor including two metallic portions separated by dielectric material to form a direct currentblocking capacitor; an annular conductive member mounted between said outer and inner conductors and having sliding electrical contact at its ends with said inner conductor, means to axially adjust theposition of said member, an annular adjustable shorting plunger between said outer and inner conductors at the other ends thereof, an energy transferring coaxial line extending at right angles to said outer and inner conductors at a location intermediate said member and said plunger, the inner conductor of said coaxial line extending into the space between said inner and outer conductors, a plurality of arcuate conductive members mounted between said outer and inner conductors intermediate said member and said tube, and means for individually adjusting radially the positions of said arcuate members.

3. A circuit fora vacuum tube having inner and outer electrode contact'rings, said circuit comprising a tubular outer conductor adapted atone end to contactsaid'outer ring, a coaxial inner conductor adapted at one end to contact said inner ring, said inner conductor including two metallic portions separated by dielectric material to form a direct current blocking capacitor; an annular conductive member mounted between said outer and' inner conductors and having sliding electrical contact at its ends with said inner conductor, means toraxiallyadjust the position of said member, an annular adjustable shorting plunger between said outer and inner conductors at the other ends thereof, an energy transferring coaxial line extending at right angles to said outer and inner conductors at a location intermediate said member and said plunger, the inner conductor of said coaxial line extending into the space between said inner and outer conductors, a plurality of arcuate members mounted between said outer and inner conductors intermediate said member and said tube, and means for individually adjusting radially the positions of said arcuate members.

4. A circuit for a vacuum tube having inner and outer electrode contact rings, said circuit comprising a tubular outer conductor adapted at one end to contact said outer ring, a coaxial inner conductor flared at one end and provided with a coaxial shoulder for contacting said inner ring, said inner conductor including two metallic portions separated by dielectric material to form a direct current blocking capacitor; an annular entirely metallic member having an electrical axial length on the order of a quarter-wavelength at the operating frequency such as to provide a reactance compensating the reactance of said tube, said member being mounted between said outer and inner conductors, closely adjacent the tube end of said inner conductor, and having sliding electrical contact at its ends with only said inner conductor, with one end of said member engaging said shoulder on said inner conductor; means to axially adjust the position of said member, an annular adjustable shorting plunger between said outer and inner conductors at the other ends thereof, an energy transferring coaxial line extending at right angles to said outer and inner conductors at a location intermediate said member and said plunger, the inner conductor of said coaxial line extending into the space between said inner and outer conductors, a plurality of arcuate members mounted between said outer and inner conductors intermediate said member and said tube, and means for individually adjusting radially the positions of said arcuate members.

References Cited in the file of this patent UNITED STATES PATENTS 2,416,080 Bailey Feb. 18, 1947 2,416,567 McArthur Feb. 25, 1947 2,424,002 Sloan July 15, 1947 2,521,364 Haller Sept. 5, 1950 2,523,122 Kuper et al. Sept. 19, 1950 2,579,511 Ostlund Dec. 25, 1951 2,617,038 Russell Nov. 4, 1952 2,633,537 Rambo Mar. 31, 1953' 2,706,802 Meisenheimer et al. Apr. 19, 1955 2,790,857 Gluyas et al. Apr. 30, 1957

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