US3826945A - Adjustable magnetically focused triode - Google Patents

Adjustable magnetically focused triode Download PDF

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Publication number
US3826945A
US3826945A US00336656A US33665673A US3826945A US 3826945 A US3826945 A US 3826945A US 00336656 A US00336656 A US 00336656A US 33665673 A US33665673 A US 33665673A US 3826945 A US3826945 A US 3826945A
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United States
Prior art keywords
shunt
tube
anode
grid
cathode
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Expired - Lifetime
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US00336656A
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English (en)
Inventor
J Behenna
G Phipps
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International Standard Electric Corp
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International Standard Electric Corp
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Publication date
Priority claimed from GB972972A external-priority patent/GB1384452A/en
Application filed by International Standard Electric Corp filed Critical International Standard Electric Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J21/00—Vacuum tubes
    • H01J21/02—Tubes with a single discharge path
    • H01J21/18—Tubes with a single discharge path having magnetic control means; having both magnetic and electrostatic control means

Definitions

  • the output power of a magnetically focused thermionic electron tube is varied by altering the strength of the magnetic focusing field.
  • the output power of an oscillator using a magnetically focused triode may be reduced over a wide range by reducing the focusing field without any detrimental increase of intercepted beam current.
  • the field is reduced by use of a magnetic shunt across the pole pieces of a permanent magnet used for focusing, the shunt being moved mechanically toward or away from the pole pieces.
  • the device may also be used to control gate current in a gate controlled tube.
  • This invention relates to magnetically focused thermionic power tubes and particularly to a novel structure for adjusting the output power thereof.
  • a thermionic gate-controlled power tube has a pennanent magnet structure arranged to produce a magnetic focusing field which may be used to minimize gate current.
  • the magnet strucure is so constructed that during use of the tube. such as in an oscillator circuit. he strength of the field can be adjusted to vary the power output of the tube over a useful range without causing cessation of oscillation.
  • mag netic field is produced by a magnet with the tube mounted between facing magnet 'polepieces.
  • the strength of the magnetic focusing field is then mechanically controlled by adjustment of the position of a magnetic shunt with respect to the polepicces to shunt an adjustable proportion of the magnetic flux flowing across the main air gap between them. in which air gap the tube is situated.
  • a thermionic gate-controlled power tube comprising a substantially U-shaped magnet having facing polepieces on opposite sides of the position occupied by the tube.
  • a shunting part of magnetic material and a control mem ber connected with the shunting part are operable to move the shunting part toward or away front the polepieces to shunt the magnet to a lesser or greater extent as desired so as to vary the strength of the magnetic field whereby. with the tube in the air gap and in use. such as in an oscillator circuit.
  • the power output of the tube is adjustable.
  • FIG. I is a diagrammatic representation of the electrodc configuration of a magnetically focused triode
  • FIG. 5 is an oscillator circuit diagram incorporating the tube of FIGS. 1 and 2 and the structure of FIG. 4.
  • FIG. 6 is a graph showing the variation in output power with magnetic focusing field obtained with the circuit of FIG. 5.
  • FIG. 1 A diagrammatic representation of the electrode por tion of a known magnetically focused tube. such as in the above British Patent. is shown in FIG. 1.
  • Filamentary thermionic cathodes 10 are mounted parallel to one another midway between and parallel to the opposite broad walls of a rectangular anode IL
  • a set of grid plates I2 is mounted with the plates edgewise on to the broad sides of anode 11 so that each cathode 10 is situated symmetrically between a pair of the grid plates.
  • the grid plates are each mounted on a respective rod 13 secured in a metal support plate 14.
  • a magnetic field H.'denoted by the arrow In use. a magnetic field H.'denoted by the arrow.
  • the tube operates as a grid-controlled tube with the grid plates providing equipotential surfaces on either side of each cathode filament. If desired the grid plates may be replaced by respective aligned sets of rods parallel to one another and to the cathode filaments. Additional rods between the edge of each grid plate and the facing anode wall may be incorporated to provide a second grid as in a beam tetrode.
  • the electrode structure is mounted on rods 15 sealed in an end. not shown. of the tube envelope.
  • the dimensions shown relate to a known type of triode. corresponding parts having the same reference numerals as in FIG. I.
  • the dimensions are in inches.
  • the length of the coated cathodes and grid or gate electrodes is 3 inches.
  • FIG. 3 shows a schematic view. in partial section. of a tube having an electrode construction similar to that of FIG. I inserted between a pair of polepieces 20 and ZI of a magnet not otherwise shown.
  • the support rods 15. appearing dotted in FIG. 3. are spaced apart with the aid of insulators l6 and 17 which also support the cathode filaments. not visible in FIG. 3.
  • the electrode structure is mounted from a ceramic base 22 and is surrounded by a water jacket 23, cooling water flowing between the anode and the wall of the water jacket via inlet and outlet pipes one of which is shown at 24.
  • the water jacket, the anode 11, the grid plates 12 of FIG. 1 as well as the support plates 14, are all made of non-magnetic material so that a virtual air gap exists between the polepieces and 21.
  • a magnetic shunt 25 is provided in order to adjust the strength of the magnetic field across the air gap between polepieces 20 and 21 .
  • the position of this shunt with respect to the polepieces 20 and 21 is made adjustable, as indicated by the arrow 26, so as to shunt the main air gap between the polepieces to a greater or lesser extent.
  • the electrode potentials may be ad justed to provide maximum power output, the focusing magnetic field strength then also having a maximum value, I'I for example.
  • I'I maximum value
  • the power output falls with a decreasing field across the air gap, as indicated in FIG. 6 in which power output is plotted against magnetic focusing field strength.
  • a reduction of the focusing field to 600 gauss is found to reduce the power output to 3 kW without significant increase in beam interception by the grid control plates.
  • the presently preferred magnet structure comprises polepieces 27 and 28 (corresponding to 20 and 21 in FIG. 3) which provide facing pole faces and which are mounted on a U-shaped permanent magnet assembly 29 by bolts such as 27a.
  • Assembly 29 comprises two U-shaped parts 30 and 31 secured to a base part 32 by means of a through clamping bolt 33.
  • Magnetic shunting plate parts 34 and 35 are slidably mounted in slots (not shown) in base 32 and each has an elongate slot 36 or 37 to clear the through bolt 33.
  • Each part 34 and 35 extends into a control base 38 mounted on the base 32 by means of plates 39 and 40.
  • a control member comprising a spindle 41 carries a gear wheel (not shown) engaging teeth (not shown) on the edges of those portions of parts 34 and 35 in the box 38.
  • the parts 34 and 35 can be moved towards and away from the polepieces 27 and 28 and the magnetic field therebetween to thus vary the magnetic field strength.
  • the tube would sit on the base in the space between the pole faces.
  • the circuit diagram shown in FIG. 5 is a tuned anode, coupled grid oscillator suitable for induction heating work. It is shown with the work coil in series with the anode tank coil to give a high output impedance, but the output may equally well be taken from the secondary coil of a work-head transformer to provide a low impedance output. The primary of the transformer is connected across the high impedance output points.
  • the anode tank circuit forms the largest unit. Because of the large r.f. currents involved. it is desirable to construct it with as few joints as possible.
  • the tank capacitance C is made up of six 4,500pF capacitors which are bolted down to a base plate and have their center lugs connected to a water-cooled bus bar. The connectors are formed from the bus bar so as to provide good thermal paths to assist in cooling the capacitors.
  • a tank coil L which consists of four 9 inch (228.6mm) diameter turns of 0.5 inch (12.7mm) copper tube, is coupled directly to the water connection on the capacitor bus bar so that the coil also is watercooled. The other end of the coil is taken to the base plate via a work coil L or primary of the work-head transformer.
  • the whole coil and busbar assembly are preferably silver-plated in order to keep circuit losses to a minimum.
  • the tube and its magnet are mounted on insulators and are coupled to the tank circuit by a 9,000pF capacitor C
  • the high voltage is fed to the tube via an inductance L of 2,500,u.H which consists of a 3 feet (91.44 cm) long single layer solenoid of number 16 gauge enamelled copper wire closely wound on a 3 inch (76.2mm) diameter former.
  • the feedback to the grid is from a coupling coil L which consists of four 11 inch (279.4mm) diameter turns of inch (9525mm) copper tube. This is mounted so that it surrounds the anode coil in the maximum coupling position and can be tilted away from the anode coil to reduce the coupling.
  • This coil is wound in the opposite sense to that of the anode coil and the end remote from the tank capacitors is connected directly to the base plate. The other end is connected to the gate terminal via a 1,000 pF capacitor and an antiparasitic choke formed from ten turns of number 16 wire on an 0.5 inch (12.7mm) diameter former.
  • d.c. return the for grid is taken via a lmH choke L to resistor R, which is between 6kQ and 8kQ, to watts.
  • the anode is fed from a source of d.c. voltage V,, between 6 and 8kV and the cathodes are grounded.
  • the density of the magnetic flux B directed from the cathode to the anode is variable.
  • Reducing the focusing field to 850 gauss is quite surprisingly found to reduce the output power to 13.6 kW, the conduction angle increasing to and the peak grid current falling to 0.4 amps, the mean grid current being 36 mA.
  • the dc. kilovoltamps supplied fell from 46.15 to 32.
  • results were entirely unexpected, and although it is believed that the construction of the particular tube may be a contributing factor, similar results may be achieved with, for example, a tube having circular concentric electrodes, radially extending grid electrodes and a variable radially extending magnetic field.
  • an electromagnetic arrangement may be used together with electrical control means operable to vary the strength of the magnetic field by controlling the current through an electromagnetic windmg.
  • the present invention thus provides a surprisingly simple means of adjusting the output power of a magnetically focused thermionic tube smoothly and over a much wider range than is obtained by complicated and expensive control equipment hitherto used.
  • a thermionic electron tube comprising an anode electrode, a cathode electrode spaced from said anode and providing an electron beam therebetween, a control grid electrode disposed alongside said cathode and electron beam, means providng a magnetic field focusing said electron beam, the magnetic field surrounding said electrodes and directed substantially parallel to the electron beam path, and means for adjusting the magnetic field strength to vary the power output from said anode.
  • the device of claim 1 comprising an open loop shaped permanent magnet having facing pole faces on opposite sides, said tube and electrodes being positioned between said opposite sides, a shunt of magnetic material disposed adjacent said magnet between said opposite sides, and a control member connected with the shunt and operable to selectively move said shunt toward and away from said pole faces to shunt the magnet to an adjustable extent to vary the strength of the magnetic field and the power output of the tube.
  • each said limb being slidably mounted in a slot in said supporting means.
  • said anode includes walls surrounding said cathode and grid, said cathode including a plurality of spaced longitudinal parallel wires, and said grid includes a plurality of spaced longitudinal parallel plates respectively positioned alternately between said cathode wires, said plates being aligned parallel with said electron beam to minimize interception thereof.

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US00336656A 1972-03-02 1973-02-28 Adjustable magnetically focused triode Expired - Lifetime US3826945A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB972972A GB1384452A (en) 1972-03-02 1972-03-02 Magnetically focused grid-controlled valves
GB973072 1972-03-02

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US3826945A true US3826945A (en) 1974-07-30

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US (1) US3826945A (en(2012))
JP (1) JPS48102970A (en(2012))
DE (1) DE2309766A1 (en(2012))
FR (1) FR2174233B3 (en(2012))
NL (1) NL7303014A (en(2012))

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1534495A (en) * 1977-05-19 1978-12-06 Standard Telephones Cables Ltd Magnetically focussed tube

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3365601A (en) * 1967-01-24 1968-01-23 Machlett Lab Inc High power vacuum tube with magnetic beaming
US3506870A (en) * 1968-03-27 1970-04-14 Machlett Lab Inc High power magnetically beamed vacuum tube with low hum
GB1195703A (en) * 1967-05-12 1970-06-24 Standard Telephones Cables Ltd Thermionic Valves

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3365601A (en) * 1967-01-24 1968-01-23 Machlett Lab Inc High power vacuum tube with magnetic beaming
GB1195703A (en) * 1967-05-12 1970-06-24 Standard Telephones Cables Ltd Thermionic Valves
US3506870A (en) * 1968-03-27 1970-04-14 Machlett Lab Inc High power magnetically beamed vacuum tube with low hum

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DE2309766A1 (de) 1973-09-06
NL7303014A (en(2012)) 1973-09-04
FR2174233B3 (en(2012)) 1976-03-05
JPS48102970A (en(2012)) 1973-12-24
FR2174233A1 (en(2012)) 1973-10-12

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