US2640946A - Ultrahigh-frequency thermionic valve - Google Patents

Description

June 2, 1953 J., BELL ULTRAHIGH-FREQUENCY THERMIONIC VALVE 2 Sheets-Sheet 1 Filed NOV. 15, 1951 FIG. 1.

JAMES B'ELL R o T N E V W 5 H M I/ I I 1 I 7 W. B u 6 (I I L 1 v 5 2 IIIIII ATTORNEY Patented June 2, 1953 ULTRAHIGH-FREQtiENoY THERMIONIC J VALVE James Bell, Pinner, England, assignor to The M-O Valve Company Limited, London, England Application November 13, 1951, Serial No. 255,896 In Great Britain November 20, 1950 This invention is concerned wtih thermionic valves and with associated circuits for use at ultra-high frequencies.

Such a circuit is known in which a triode valve is used and the output circuit is constituted by a resonant cavity, constituted for example by a coaxial line, connected between the grid and anode of the valve. The frequencies of operation of such a circuit are determined by the size of the resonant cavity and the value of the interelectrode capacitance between the grid and anode of the valve, the frequency being different for each mode in which the circuit is capable of operating. Since it is impracticable to dispose the resonant cavity wholly within the envelope of the valve the size of the cavity cannot be reduced below a certain minimum which is determined by the configuration of the envelope of the valve. Also the interelectrode capacitance'dep'ends upon the area and the spacing of the electrodes, the former being determined by the output power required and the latter by the required operating frequency and the operating anode voltage. Thus, with a given set of operating conditions, the maximum operating frequency of such a thermionic valve circuit when operating in its fundamental mode is automatically determined.

It is an object of the present invention to provide a thermionic valve circuit for use at ultrahigh frequencies in which the maximum operating frequency of the circuit when operating in its fundamental mode may be made considerably higher than in the known arrangement described above, without reducing the area of the electrodes of the valve or increasing the interelectrode spacmgs.

It is a further object of the invention to provide a thermionic valve circuit for use at ultrahigh frequencies having a higher efiiciency than the known arrangement described above.

It is yet another object of the invention to provide a thermionic valve for use in such an improved circuit.

Accordin to one aspect of the present invention a thermionic valve circuit for use at ultrahigh frequencies comprises a triode valve and an output circuit consisting of two resonant cavities electrically connected between the grid and anode of the valve in such a manner that part only of the interelectrode capacitance between the grid and anode of the valve is effectively connected across each cavity. Preferably the two resonant cavities are substantially identical and the arrangement is such that substantially half of the interelectrode capacitance between the grid and 2 Claims (Cl. 313255) anode of the valve is effectively connected across each cavity.

According to another aspect of the invention a. triode valve for use in a circuit according to theinvention comprises a thermionic cathode, acylindrical grid disposed around the cathode, a cylindrical anode disposed around the grid, an envelope of insulating material, a first metal disc sealed through the envelope and electrically connected to the anode, and second and third metal discs sealed through the envelope respectively on opposite sides of the first disc and electrically connected respectively to opposite ends of the grid. Preferably the first disc is electrically connected to a part of the anode at the centre of its length.

One arrangement in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of a triode valve in accordance with the invention for use at ultrahigh frequencies; and

Figure 2 is a view of an amplifier circuit in accordance with the invention'for use at ultrahigh frequencies, the circuit incorporating a valve such as is illustrated in Figure 1 and the circuit elements external to the valve being shown in section.

Referring to Figure 1 of the drawings, the triode has a substantially circular cylindrical glass envelope I and. has a circular cylindrical thermionic cathode 2, grid 3 and anode 4 all disposed coaxial with the envelope I.

The cathode 2 is provided with a suitable electron emissive oxide coating on its outer cylindrical surface and is supported by a tubular metal member 5 which is secured to a metal tube 6 which is sealed through one end of the envelope 1 and forms a lead-in connection for the cathode 2. The cathode 2 is heated by a heater 1 one end of which is connected to the cathode 2 and the other end of which is connected to a lead 8 which is sealed through the envelope I and is connected to a metal pin 9 which is insulated from the tube 6 by a block of insulating material I0 disposed in the tube 6.

The anode 4 is supported by means of an annular metal disc ll sealed through the envelope I, the disc ll being electrically and mechanically connected to the anode 4 midway along its length and serving as a lead-in connection to the anode 4.

Also sealed through the envelope I on opposite sides of the disc II are two annular metal discs l2 and I3 which are provided respectively with flanges l4 and I5. The disc [2 is electrically connected to one end of the grid 3 via metal members I6 and I1, while the disc [3 is electrically connected to the other end of the grid 3 via ametal member I8 so that thediscs l2 and I! serve as lead-in connections to .the grid 3.

Referring now to Figure 2 of the drawings, the valve l9, which is of the form shown in Figure 1 and is therefore only represented diagrammatically, is connected in an ultra-high frequency amplifier circuit. The input circuit is connected between the cathode 2 and grid 3 of the valve l9 and consists of a coaxial line having inner and outer conductors 20 and 2| respectively and tunable by means of a fingered piston 22, the input signal being fed in via a coaxial line 23 and probe 24. The valve I9 is plugged into the circuit so that the tube 6 is disposed in and makes contact with the end of the conductor '20 while the flange of the disc 13 is disposed in and makes contact with the end of the conductor 2|, which is provided with spring fingers for this purpose. The conductor 20 is hollow, and through it passes a conductor 25 which makes contact with the pin 9 so that a voltage may be applied to the heater 1 of the valve IS.

The output circuit is connected between the grid 3 and, anode 4 of the valve 19 and consists of a pair of substantially identical coaxial lines, one having inner and outer conductors 2i and 2 6 respectively and the other having inner and outer conductors 21 and 28 respectively. The two coaxial lines are tunable by means of fingered pistons .29 and 30, and the output signal is taken oil by means of :a probe 31 and coaxial line .32. When the circuit is assembled the flange H of the disc I2 is disposed in and makes contact with the end of the conductor 21, which is provided with spring fingers for this purpose.

The disc ll makes contact with a metal block 33 which is capacitatively coupled .to the conductors 26 and 28 via annular mica insulators 34 and 35 respectively.

The block 33 is secured to the conductors 26 and 28 by means of bolts such as 36, which are insulated from the conductors 26 by means of insulating tubes such as 31 and insulating washers such as 38. The disc II is thus connected to the conductors 26 and 28 at the operating frequency of the circuit, but there is no direct current path between the grid 3 and anode 4 of the valve I9.

It will be appreciated that only half of the grid-anode capacitance of the valve I9 is ef- Iectively connected across each of the resonant cavities constituted by the coaxial lines 2|, '26 and 21, 28 respectively, and that the resonant frequency of the combined valve and cavities is therefore much greater than would be the case if the known arrangement referred to above were used with the same electrode dimensions. Furthermore, the cavity losses will be reduced as compared with the known arrangement resulting in greater efficiency of operation.

I claim:

1. A triode valve comprising a thermionic cathode, a cylindrical grid disposed around the oathode, a cylindrical anode disposed around the grid, an envelope of insulating material containing the cathode, grid and anode, a first metal disc sealed through the envelope and electrically connected to the anode and second and third metal discs sealed through the envelope respectively on opposite sides of the first disc and electrically connected respectively to opposite ends of the grid.

'2. A triode valve according to claim 1, in which the first disc is electrically connected to a part of the anode at the centre of its length.

JAMES BELL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,405,261 Whinnery July 16, 1946 2,421,591 Bailey June 3, 1947 2,510,639 .Koch June 6, 1950

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