US2462082A - Thermionic valve - Google Patents

Description

J. FOSTER THERMIONIC VALVE Feb. 22, 1949.

2 sheets-sheet 1 Filed Oct. 28. 1942 Invenior Jan, 'Faster'.

Attorney Feb. 22, 1949. J. FOSTER THERMIONIC VALVE I Filed om. 2a, 1942 2 Sheets-Sheet 2 MMV Attorney Patented Feb. 22, 1949 THERMIONIC VALVE .lohn Foster, London, England, assignor, by mesne assignments, to International Standard Electrie Corporation, New York, N. Y., a corporation of Delaware Application October 28, 1942, Serial No. 463,701 In Great Britain December 19, 1941 8 Claims.

. The present invention relates to electron discharge devices for use at ultra high frequencies of the kind in which the electron stream is density modulated by controlling the iiow of electrons from the cathode and the density modulated beam is employed to excite a hollow resonator from which the output is obtained.

Such devices of the type specified have many advantages over other known elect-ron discharge devices for use at ultra high frequencies, such as those working on the electron velocity modulation principle or electron deflection principle. in particular the noise level in devices in which the electron ow is controlled is much lower than in the other types.

In order to adapt the well known grid controlled electron ow multielectrode valve comprisingA a cathode, anode and control grid for use at ultra high frequencies, it is necessary to eliminate troubles due firstly to electron transit time eiiects, and secondly to the coupling between the input and output circuits in the form of interelectrode capacities, and selfand mutual-inductances of the leads.

The troubles due to the coupling between the input and output circuits have been overcome in the kind of device to which this invention relates by using the density modulated beam to excite a resonant chamber from which the output is taken. Such a device operates eiciently as a wide irequency-band amplifier, and has a low noise characteristic as opposed to beam velocity and deflection controlled devices.

Itis the object of this invention to provide an improved device of the kind hereinbefore specied of simpler construction than known devices of that kind.

According to the invention such a device comprises a cathode, a control'grid and an anode or collecting electrode, a U-shaped metallic member containing said cathode and control grid parallel to the base thereof, a pair of metallic plates spaced in the direction of electron flow from the limbs of said U-shaped member to form a first gap between said plates and limbs and spaced from the anode or collecting electrode to form a second gap between said plates and anode and a metallic disc sealed into the Wall of the device and having an aperture therein to allow of the passage of the electron stream therethrough and adapted to form a part ofv a hollowl resonator' arranged to be inductively excited by the passage of the electron stream across the said second gap.

The invention will be further described by way of example as embodied in the electron discharge device illustrated in the accompanying drawings, in which Figures 1, 2 and 3 are plan, side and end views respectively, with the glass envelope of the device shown in section, as well as the outer wall of the resonator in Fig. l, Figure 14 shows a detail in section.

Referring to the drawings, the electron discharge device comprises an electrode assembly which consists of a cathode l,control grid 2 andsecond grid 3. The cathode is connected to a u -shaped electrode 4 whose base is constructed to form a Condenser, with a plate v2 as hereinafter described in connection with Fig. Ll. Thegrid 3 is connected to this condenser by a very short lead l5 of low self inductance. 'This almost climi. nates any tendency to instability. Theleads 5 and 5a are connected to thecontrol grid 2 by means of ashort conductor 29 and the leads c and Ea are connected to the cathode by means ofconductor 22. These leads form a comparatively low loss path for the introduction of the signal. The input circuit between 5 and 6 or Ea and 6a could conveniently be a screened Lecher system. The cathode heater current leads 'i and 8 are passed through the press I6 in well-known manner as well as theD. C. voltage lead 9 forgrid 3.

One side only of the cathode l is coated with electron emissive material and the electrons after passing throughgrid 3 are formed into a narrow beam indicated at il by the electron lens formed by the gap IB between shields id and U-shaped electrode 4. This beam passes through an aperture I2 in a copper disc Il sealed in .the glass envelope and impinges on the anode i3.

The electrodes 4 and l0 are mounted on rods or wire bars which are supported in two parallel mica plates i9 and 20. Springs 2l are mounted on and in direct electrical contact with two of the said bars, and when the electrode assembly is placed in position the springs press against the disc I l and so make good electrical connection between the disc H and the shield electrodes it.

The condenser incorporated in the base ci the U-shaped electrode i is shown more clearly in Figure 4 and compri-ses a metal plate 2i sandwiched between two sheets of mica, as shown in the drawing. These three elements are then sandwiched between the bottom of the U-shaped electrode and a channel shaped member 2i' the ends of which are .soldered or welded to the limbs of the electrode 4. The centre plate 'i oi the condenser is provided with a tab at each end thereof. In Fig. 4, only onetab 26 is visible, the position of theother tab 25 being shown in the drawing. lOne of these tabs, namely 25 is connected to thegrid 3 by the short lead I5, as already stated and theother tab 24 is connected to thelead 9 which is brought out through the press I6 and enables a positive potential to be applied to thegrid 3. The other plate of the condenser formed by the base of the electrode 4 andmember 2| is connected to the cathode by means of aconnector 22.

The ends of the electrodes I are brought in close proximity to each other and are provided withparallel portions 23 which pass through the aperture I2 in the disc Il and enable the input structure to be aligned with the aperture I2. The length of theseportions 23 may be such as to leave a gap between these members and the anode I3 of the order of .100 inch. Y

In use a high-Q coaxial resonator 26 (Fig. 1) is plaoed on the anode I3 and disc II or other resonant chamber may be mounted on the disc I I to present a high impedance to the beam.

When an ultra-high-frequency -signal is fed into thegrid 2 the beam becomes space-chargedensity Imodulated and thus excites inductively the output resonator as it passes from the aperture I2 to the anode I3. As this time is short the output efliciency is very nearly 100%. The transit time of the electrons from cathode to anode introduces a phase change between the input and output voltages, but is otherwise of no importance. The use of reasonably hiigh voltages enables the distance from the anode I3 to the aperture I2 to be quite large thus rieducing the output capacity to a low value.

The voltages applied to the control grid may be of the order of -1.5. volts, to thegrid 3 of the order of 150 volts, to the disc II, shield electrodo I0 and anode I3 of the order of 700" volts, and the U-shaped electrode li at zero volts or cathode potential.

In one practical case Mif- Input capacity 6.0 Output capacity 0.5 Y Feedback capacity .0005

The emission current was 8.0 ma., and was controlled by the potential on the control grid giving a slope of the characteristic curve of 6.5 ina/v.

Gain at 600 megacycles per second with 4 rnegacycles per second band Width=28 decibels.

The advantage of the electron discharge device according to the invention for amplification of ultra high frequencies are:

(l) Elimination of input damping due to cathode lead inductance.

. (2) Elimination of instability, the acceleratinggrid 3 to cathode decoupling condenser (contained within the base of the U-shaped electrode il) being connected to these electrodes by short leads of low indu-ctance.

(3) Low output capacity enabling use of a high Q resonator, thereby increa-sing the gain and increasing the frequency band width.

(4) Elimination of instability due to anodegrid capacity, this being reduced to a negligible quantity.

(5) The low noise characteristic of spacecharge controlled devices as opposed to Velocity and deiiection controlled devices.

What is claimed is:

1. An electron discharge device for use at ultra high frequencies comprising a cathode, a control grid, and an anode, a U-shaped metallic member having flat parallel limbs containing said cathode and grid spaced from the base thereof, a pair of metallic plates substantially in the planes of said limbs and spaced in the direction of electron ow from said limbs forming a first gap between said plates and limbs and spaced from said anode forming a second gap between said plates and anode, and a metallic disc sealed into the wall of the device and forming part of a hollow resonator, said disc being positioned between said rst and second gaps and having an aperture therein to allow of the passage of the electron stream therethrough.

2. An electron discharge device according toclaim 1 wherein the ends of said plates near the anode are brought into close proximity to each other and are provided with parallel portions which pass through the aperture in the said metallic disc.

3. An electron discharge device according toclaim 1 further comprising means for making separable direct electrical contact between said plates and disc, said means being supported on one of said last mentioned elements and adapted to engage the other.

4. An electron discharge device according to claim l further comprising spring members se'- cured to metallic supporting bars for said plates and adapted to press against said metallic disc for making the electrical connection therewith.

5. An electron discharge device according toclaim 1 further comprising straight parallel wires which pass through the envelope of the device and arc connected with the cathode and control grid, respectively, to form a low loss path for the input of the device.

6. An electron discharge device according toclaim 1 further comprising an accelerating electrode and a decoupling condenser connected between said accelerating electrode and cathode, said decoupling condenser being incorporated in the base of said U-shaped member and connected directly to said accelerating electrode and cathode.

7. An electron discharge device according toclaim 1 comprising a connection between said cathode and said U-shaped member.

8. An electron discharge device according toclaim 1 further comprising an accelerating elec-l trode and the base of said U-shaped member comprising a double Wall, a decoupling condenser compri-sing a metallic sheet sandwiched between two mica sheets contained within said double wall, said sheet having two tabs, one connected by a short lead to said accelerating electro-de and the other connected to a lead passing through the envelope of the device.

JOHN FOSTER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS

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