US2314065A - Cathode - Google Patents

Description

'March 16, 1.943. R B AYER 2,314,065

CATHODE Filed March 7, 1942 INVENTOR Raymond B. A l/er B am - ATTEIRNEY Patented Mar. 16, 1943 CATHODE Raymond B. Ayer, Verona, N. J .,V assigner to Radio Corporationof America, a corporation of Delaware Application March 7, 1942', Serial No. 433,750

(Cl. Z50-27.5)

Claims.

My invention relates to electron discharge devices of the transmitter or power type, particularly to fllamentary cathodes for such devices.

Filamentary cathodes in transmitter or power tubes designed for single phase power supply are limited in length and in operating voltage. Long slender filaments are diilicult to support, braces of insulating ceramics and the like which contact the filament deteriorate and crumble at operating temperatures, and high operating voltages for the lament cause hum in the tube output. There are practical limits to the current rating and cross sectional area of the filament because of the mechanical difficulties in shaping heavy filaments from the brittle refractory metals, such as tungsten, and because of the increased cost of high current-low voltage power supply equipment.

An object of my invention is a fllamentary cathode for transmitter or power tubes in which the voltage as well as the current for high cathode power is moderate.

Another object of my invention is a fllamentary cathode for power tubes, which has moderate current requirements, low voltages between filament lead-in conductors, which produces negligible hum in the tube output, which is rugged in construction, and which is easy to manufacture.

The characteristic features of my invention are defined in the appended claims and one embodiment thereof is described in the following specification and shown in the accompanying drawing in which Figure 1 shows a longitudinal section of a fluid-cooled transmitting tube having my improved fllamentary cathode, Figure 2 is an elevational View of the operative portion of my improved cathode, Figure 3 is an end View of the cathode of Figure 2, and Figure 4 is a wiring diagram of the filament coils of my improved cathode.

One electron discharge device in which my improved cathode is particularly useful comprises an envelope with a conventional fluid-cooled anode I sealed at its upper end to a glass bulb 2, through which the grid and iilament lead-in conductor may be sealed. T'he grid 3 may be wound on side rods and supported on a clamp around the reentrant stem at the outer end of the bulb. The usual heat and electron shields ll and 5 may be placed across the end of the anode to protect the glass portions of the envelope.

The cathode 6 comprises, according to my invention, a plurality of end-to-end coaxial helices or spirals 1, 8 and 9 of coiled wire supported, in the particular illustrated embodiment, on three parallel spaced filament support rods and current conductors I, I I and I2. Each support rod is mechanically supported in the glass bulb and is externally connected to current supply terminals. The end of each coil is bent out of the cylindrical surface of the coil and is attached, as by binding or welding, to one of the support rods. The opposite ends of each coil is attached to a different rod, the connections being made so that'the lilament presents a polyphase loadlto cathode terminals of the tube. The particular coil connections shown are of the delta type and are diagrammatically as shown in Figurel. By making the ohmic resistance of the coils equal, a-balanced three-phase power supply may be applied to the three-filament terminals and the cathode operated with negligible hum disturbance.

A lament, with a given current and power rating, has, when constructed according to my invention, an operating voltage of only 57.6% of the operating voltage of a corresponding filament made in the usual way with single phase connections. Further, my improved filament with three distinct coils, supported at six points, is to be distinguished from a corresponding filament with a single coil for single phase power supported only at two widely spaced points. The increased rigidity of my lament is of particular importance in tubes that must withstand rough handling and vibration in use.

My improved filament is particularly adapted for power tubes of the type shown in the Zottu et al. Patent 2,228,939, January 14, 1941, where the total lament power is of the order of 7.0 kilowatts, where the operative length of the filament is '7 inches, and Where its diameter is 1 inch. Tungsten or thoriated tungsten wire may be used.

Should increased rigidity of the coils be desired, each coil, 1, 8 and 9, may be divided into sections of uniform length and the sections connected to corresponding pairs of support rods and operated in electrical parallel. Further, the iilament may be arranged to operate with polyphased power with any desired number of phases. The coils may be supported on and connected to three support rods for three-phase operation as shown, or for quarter-phase operation. Six-phase operation, for example, may be obtained with six rods and six coils. Should star or Y polyphase connections be desired, the number of support rods must, of course, exceed by one the number of phases used. Should single phase operation be desired, the corresponding ends of the several coils would be connected to a common support rod or to different support rods electrically connected in parallel.

The support rods I0, Il and l2 are preferably disposed along the inside of `the illament coils and the ends of the coils bent inwardly and attached to the rods as shown, but if desired the rods may be disposed outside the coils, where the spacing between the cathode and grid permits.

My improved lament is adapted for transmitter or power tubes, is not limited in its overall length and may be operated for a given power at moderate voltages. My improved filament produces a minimum of hum disturbance in the output of its tube, is rugged in construction and is easy to manufacture.

I claim:

1. A filamentary cathode comprising a plurality of coaxial helices, support rods for said helices arranged longitudinally of the helices, the end of each helix being bent from the surface of its cylindrical surface and attached to one of the rods, the electrical connections to the rods being arranged so that the electrical resistance through the helices between any pair of rods is uniform.

2. A polyphase cathode comprising a plurality of coaxial coils, a plurality of parallel spaced metal current conducting support rods disposed lengthwise of said coils, the ends of said coils being mechanically attached to said rods, the electrical connections of the coils to the rods being arranged to present a balanced polyphase electrical load to the rod terminals.

3. A cathode for power tubes comprising a plurality of end-to-end helices of electron emissive wire, a plurality of parallel support rods, the rods being disposed lengthwise of the helices and in spaced relation to the surface of the helices, the ends of the helices being mechanically and electrically attached to said rods.

4. A three-phase cathode comprising three end-to-end coaxial helices, three spaced parallel metal support rods in and disposed lengthwise of the helices, the opposite ends of each helix being connected to a different pair of said rods to provide a balanced uniform electrical load between each of said pairs of rods.

5. An electron discharge device comprising a tubular anode and a cathode, said cathode comprising an electron emissive filament spiralled in a substantially cylindrical surface and disposed substantially coaxial with said anode, and means to supply current to a plurality of points on said lament intermediate its ends and to rigidly support said filament in xed spaced relation with said anode, said means comprising a plurality of spaced metal rods supported at one end of the electron discharge device and extending in parallel relation to the opposite end of the device, the filament wires being bent out of said cylindrical surface at a plurality of intermediate points along the length of the cathode, and connected to said rods.

RAYMOND B. AYER.

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