US 2712096 A
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June 28, 1955 E. P. MaCKENzlE ETAL l2,712,096
VACUUM TUBE v Filed June 22, 1950 I N V EN TOR. fan/Awa f? Mac /fwz/f BY daaa/v A( Woas United States Patent@ VACUUM TUBE Edward P. MacKenzie and Gordon K. Woods, Grosse Pointe, Mich.
Application June 22, 1950, Serial No. 169,576
8 Claims. (Ci. 315-58) This invention relates to vacuum tubes for electronic application in the generation, amplification, rectification or reception of radio or audio frequency alternating currents and is particularly directed to the attenuation of harmonic and parasitic emissions or" frequencies departing from the fundamental of the circuit in which the tube is operating.
The ever-increasing use of radio frequency transmission in iields of commercial and amateur radio broadcasting, television and aviation, police, maritime, postal telegraph, wireless telephony and numerous other public and private communication systems provides a corresponding ever-increasing need for accurately stable transmitting frequencies and effective suppression of interfering spurious and harmonic emissions.
Commercially available vacuum tubes are conventionally designed to operate over a wide range of frequencies and are accordingly susceptible of transmitting parasitic and harmonic oscillations, departing widely from the operating frequency, external anti-parasitic and harmonic suppressing circuits being relied upon to attenuate such interfering emissions.
The present invention contemplates the integral incorporation within the vacuum tube itself of suppressing circuits which will attenuate the emission of oscillations of a frequency higher than a predetermined fundamental operating range.
More particularly, it is contemplated that a capacitance of predetermined value, depending upon the design and application to which the tube is to be put, be introduced from one or more of the electrodes to electrical ground through the integral incorporation within the tube envelope itself of suitable condensers in such circuits.
The advantages sought by such an approach include the elimination or reduction of lead wire inductance between the electrodes and conventional external suppressing circuits; the elimination or reduction of tendencies for external suppressing circuits to set up self-resonance at unwanted frequencies; the use of the vacuum within the tube as the condenser dielectric providing a relatively high capacitance which will facilitate the use of relatively small units having inherently low inductance and also providing protection against dielectric destructive arcing from voltage overload; and the use of the grounded condenser element as an eiective shield against stray fields.
While this approach to the suppression of spurious and harmonic oscillations necessarily` limits the maximum applicable operating frequencies for any particular tube and, therefore, calls for a relatively wider variety of limited purpose tubes from a manufacturing standpoint, the present invention also contemplates a constructional design which will facilitate the incorporation of desired values of capacitance with a minimum of modification in construction between tubes with different ratings.
Another object of the invention is to employ the anode itself as one element of a condenser providing a low impedance path to ground for spurious, harmonic and 2,712,096 Patented June 28, 1955 Flice self-resonant frequencies, in order to conserve space, simplify construction and entirely eliminate any lead inductance between the anode and its condenser.
Another object is to construct each side of the filament lead within the tube envelope to act as the lame'nt coupled element of a condenser from the filament to electrical ground in order to provide a low impedance path to ground for radio frequencies and substantially eliminate the lead inductance incident to external condenser circuits.
Another object is to similarly provide a grid lead construction within the tube envelope adapted to serve as one element of a condenser providing a low impedance path to ground for spurious and harmonic frequencies in the signal voltage as well as the attenuation of selfresonant tube circuits.
Another object is to employ a single grounded condenser element to cooperate with two or more of the electrode coupled condenser elements in order to con serve space and simplify construction.
Another object is to position such common grounded element so as to serve as an effective shield against the influence of outside stray fields.
Anotherobject is to employ electrode coupled condenser elements adapted to provide maximum desired capacities for a wide range of frequency operation, together with a basic form for the grounded condenser element likewise adapted to provide such maximum capacity so as to permit effective modification of capacity for one or more of the 'electrodes through the simple provision of appropriate perforations in adjacent condenser surfaces, thus reducing constructional modification for a wide range of various tube ratings to the simple variation of the extent of perforation in an otherwise uniform condenser element.
Another object is to provide a preferred embodiment wherein a single cylindrical tubular condenser element is adapted to be mounted in the base of the tube and to surround concentric inner-elements of the condensers formed respectively by a cylindrical anode at one end of the tube and cylindrical segments formed to serve as internal lament and grid leads atl the other end of the tube.
These and other objects will be more apparent from the following detailed description and from an examination of the drawings disclosing such preferred embodiment wherein:
Fig. l is a schematic circuit diagram of a vacuum tube employing internal electrode coupled condensers;
Fig. 2 is a partially diagrammatic perspective view of a vacuum tube showing the relative constructional location of the significant elements; and
Fig. 3 is a perspective view of the grid coupled condenser element of Fig. 2 perforated for lower capacitance.
'Referring to Fig. l, it is seen that a vacuum tube envelope 10 encloses conventional anode 11, control grid 12, and filament 13, electrodes and may include a screen grid 1A and a suppressor grid 15, if tetrode or pentode characteristics are desired or may exclude all grids if diode operation is involved such as in rectifying high voltage. The significant electrical circuit insofar as the present invention is concerned involves the incorporation within the tube envelope of one or more condensers C-l, (2 2, C-3, C-4, C-S, from one or more of the electrodes to electrical ground 16.
Each of these condensers, depending on its capacitance rating, provides a low reactance path for harmonics, parasitic and self-resonant frequencies higher than the fundamental of the predetermined maximum operating frequency. By providing condensers for each of the electrodes, such harmonics or spurious oscillations in filament heating current, and signal or control voltages as well as oscillating effects traceable to inductance of lead wires and inter-electrode parameters will be effectively eliminated or attenuated at the source of their emission.
Referring to Fig. 2, it will be seen that the preferred embodiment, which for purposes of simplifying the disclosure is shown as a triode, employs a cylindrical anode 11, surrounding a spiral grid 12 within which a pair of parallel vertical filaments 19a and 19b extend, the ends of which are electrically connected at points 23a and 20h in the insulator mounting disc 21.
The filament leads within the glass envelope .10 include a pair of cylindrical segments 23a and 23!) while the grid lead which extends to a point 24 in the disc 2l includes a cylindrical segment 25. The anode 11 and each of the cylindrical segments 23a, 23h and 25 lie in concentric relationship inside of a cylindrical tubular element 26 in a manner adapted to provide readily determinable capacitance through the vacuum dielectric therebetween. The outer tube 26 is adapted through a lead 27 to be electrically grounded thereby serving .as rthe grounded condenser element for the respective anode l1, filament grid coupled condenser elements 23a, 23h and 25. Suitable dielectric refractory spacer rings 28 may be employed to accurately space the anode 1l, which in itself acts as one element of its condenser, from the grounded condenser element 26 and like means 28a may be employed to secure accurate spacing of the cylindrical segments 23a, 23h and 25 with respect to the lower adjacent portion of the grounded condenser element 26. In the case of the grid and lament cendensers where power and heat values are relatively low, suitable mica, plastic or other dielectric materials might be employed in order to secure a close spacing of condenser elements.
By choosing appropriate size and spacing for the various condenser elements, a suitable maximum capacitance may be provided for attenuating oscillations exceeding a relatively low fundamental operating frequency, while requirements for progressively higher maximum operating frequencies may be incorporated by employing a like grounded condenser element 26 which is perforated to any extent desired in order to reduce the effective area andv capacitance between one or more of the respective electrodes and electrical ground. Thus, from a manufacturing standpoint, a wide variety of maximum frequency tube ratings may be made to depend entirely on the extent of perforation adjacent the respective electrode coupled condenser elements in the single grounded condenser element 26, such element having identical basic form in each case, or the perforation might be incorporated in the electrode coupled condenser elements, as the' grid coupled condenser element 25 shown in Fig. 3 in order to effect different ratings for otherwise standard tube constructions.-
A suitable anode lead 29 may be provided through the top of the glass envelope 10 in accordance with standard commercial practice. The grounded condenser elements 26 may be suitably mounted in the base 30 of the tube and serve to support the internal anode 11, insulator disc 21 and condenser elements 23a, 23h and 25.
In other respects, appropriate mounting provision for the grid and filament may be made in accordance with conventional practice including, for example, a filament support 31.
It will be understood that if a screen grid were employed, four cylindrical segments might be provided with one serving as the screen grid coupled condenser element.
While a particular embodiment has been described Yherein in substantial detail, it will be understood that numerous modifications might be resorted to without departing from the scope of our invention as set forth inthe following claims.
l. A vacuum tube for use in electronic circuits, including means for attenuating spurious and harmonic emissions departing from the desired fundamental operating frequencies comprising an anode, a cathode, a control grid and fixed condensers within the vacuum tube envelope for each of said electrodes adapted to provide a predetermined fixed capacitance to an exposed lead conductor which may be grounded.
2. A vacuum tube as set forth in claim l employing a common grounded condenser element.
3. A Vacuum tube for use in electronic circuits, including means for attenuating spurious and harmonic emissions departing from the desired fundamental operating frequencies comprising an anode, a cathode, a control grid, a shield around said electrodes adapted for connection to an electrical ground, said anode being adapted to serve as one element and said shield as the other element of a condenser for providing a predetermined fixed capacitance from said anode to electrical ground, the leads for said cathode and control grid also ,being adapted to operate as fixed condenser elements cooperating with said shield to provide a predetermined xed capacitance respectively from said control grid and cathode to an exposed lead conductor which may be grounded.
4. A vacuum tube for use in electronic circuits, including means for attenuating spurious and harmonic emissions departing from the desired fundamental operating frequencies comprising a plurality of electrodes, a shield surrounding said electrodes adapted to serve as one element of a condenser from at least one of said electrodes to an exposed lead conductor which may be grounded, the capacitance thereof being adapted for tubes having different ratings through the use of a Varied degree of perforation in adjacent condenser surfaces providing a varied degree of effective condenser area.
5. A vacuum tube for use in electronic circuits, including means for attenuating spurious and harmonic emissions departing from the desired fundamental operating frequencies comprising a cylindricalanode, a cathode, a control grid, said cathode and control grid being adapted to extend within said cylindrical anode, a cylindrical condenser element surrounding said anode and extending beyond an end thereof, grid and cathode leads including cylindrical segments adapted to extend Within and adjacent to the extending portion of said condenser element, said anode and cylindrical segments being adapted to co-act with said surrounding condenser element to establish a predetermined capacitance from each of said electrodes to an exposed lead conductor which may be grounded.
6. A vacuum tube as set forth in claim 5 wherein said surrounding condenser element is adapted to directly locate and support said internal condenser elements in accurately spaced relationship, varying perforation being employed to change the effective area between adjacent condenser surfaces in tubes with different ratings.
7. A vacuum tube for use in electronic circuits, including means for attenuating spurious and harmonic emissions departing from the desired fundamental operating frequencies comprising a directly heated cathode, and a condenser within the vacuum tube envelope adapted to provide a predetermined capacitance between said cathode and an exposed lead conductor which may be grounded, one element of said condenser extending between the base and said cathode being adapted to serve as an electrical lead for said cathode within the tube envelope.
8. A vacuum tube for use in electronic circuits, including means for attenuating spurious and harmonic emissions departing from the desired fundamental operating frequencies comprising a cathode, a pair of internal leads for said cathode, said leads per se each being adapted to serve as elements of a condenser, and a groundable condenser element cooperating with each of said lead condenser elements for providing a predetermined capacitance from said cathode to electrical ground.
References Cited in the le of this patent 6 Gill Mar. 19, 1935 Lindenblad June 8, 1937 Ferris Mar. 5, 1946 McArthur Aug. 3, 1948 Johnson et al. Sept. 27, 1949 Anthony et al. Apr. 4, 1950 Stevens Dec. 12, 1950