US1834443A - Cathode system for vacuum tubes - Google Patents

Description

Dec. 1, 1931. s. BALLANTINE GATHODE SYSTEM FOR VACUUM TUBES Filed Aug. 6, 1928 2 Sheets-Sheet l W 3 7 0 6 Mn L M "A In] Carl/re 75p w a 7M Hami Dec. 1, 1931. s. BALLANTINE CATHODE SYSTEM FOR VACUUM TUBES 2 Sheets-Sheet 2 Filed Aug. 6, 1928 gwvw tz $41M al/w Patented Dec. 1, 1931 PATENT OFFICE STUART BALLANTINE, OF MOUNTAIN LAKES, NEW JERSEY GATHODE SYSTEM FOR VACUUM TUBES Application filed August 6, 1928. Serial No. 297,746.

This invention relates to vacuum tube devices and to electrical circuits therefor. More particularly, it relates to that class of vacuum tube devices in which electron emission is obtained from a cathode system which is heated by alternating current. Such a cathode system may be associated, in a vacuum tube device, with a suitable anode or plate, as a rectifier, or in conjunction with one or more control elements or grids, as is common in three electrode and four electrode vacuum tubes, or may be otherwise employed.

"The invention will be described in connection with a vacuum or audion tube of the type. ordinarily used in the telephone and radio arts, although it must be understood that this is only one example of the many applioations-of my invention, which extends to X-ray, rectifier, and other kinds of vacuum tubes. l

A method of heating the cathode of an audion or vacuum tube by means of alternatin current without causing a disturbing electrical pulsation in a circuit associated with the tube has long been sought. In a radio receiving set, for example, if the filaments of the vacuum tubes are directly heated by alternating current it is very diflicult to avoid a hum in the telephones or sound reproducing apparatus. My invention over.- comes such difliculties, and provides a method and means whereby the cathode or filament system of a vacuum tube may be supplied with alternating current without the production of undesirable electrical pulsations in the circuits associated therewith.

According to my invention I arrange the cathode system in the form of a plurality of elements having a suitable geometrical arrangement and supply at least one element with alternating current of a difl'erent phase from that supplied to another element. A0-

cording to a preferred embodiment of my invention, I supply such elements, in pairs, with alternating currents bearing substantially a quadrature phase relation, so that the current in one element of the cathode system is approximately 90 difierent in phase from the current in another element of the cathode system. According to my invention, these elements may be arranged either in the same tube, or in separate tubes which are associated externally.

Various arrangements for carrying out my invention are shown in the accompanying drawings, in which Figure 1 illustrates a vacuum tube provided with a two-element cathode; Figure 2 illustrates a suitable method of supplying out-of-phase currents to a plurality of cathode elements; Figure 3 shows another method of accomplishing this result; Figure 4 shows in detail a method of connection to a single tube; and Figure 5 shows an arrangement involving two tubes connected in arallel according to the present invention.

simple illustration of the principle of the present invention is given in Figure 1, which shows a vacuum tube 1 having plate P, grid G, and a cathode arranged in the form of two filamentary elements F and F These elements may or may not have a common point or centre tap arrangement. If a centre tap is employed, it may be either internalor external, and may, if desired, make use of a suitable impedance, for example, a resistance, shunted across each cathode element. The elements F and F of the cathode system are,in this instance, supplied with alternating currents which bear a substantially quadrature relation to each other; that so is, the current in one element leads the current in the other element by approximately 90. If the instantaneous voltage across one cathode element is represented by e =E sin at then the instantaneous voltage across the second or complementary element may be represented by e =E cos mt, the symbols having their well-known mathematical meanings.

I have found that by this means the hum is greatly reduced or substantially eliminated. This result I attribute to the fact that a large hum-producing component is proportional to the square of the voltage drop in each element of the cathode. Since sin wt'l' cos wt= 1, it follows that e +c is theoretically constant, and the arrangement produces an analogous result to that which is obtained when the cathode is heated by a constant current.

The geometrical configuration of the elemo ments of the filament stem may be varied considerably, and it is o vious that any number of elements may be arranged and supplied in the foregoingmanner. In general, it is useful to arrange the elements in equal or complementary pairs, and a geometrically symmetrical arrangement is suitable.

That portion of the bum which is due to temperature variation of Joule effect in the cathode system is not, in general, eliminated by the arrangement described above, and is suitably reduced or overcome by providing massive cathode elements of high thermal capacity.

Any suitable method of supplying out-ofphase currents to difi'erent elements of the cathode system may be employed. In Figure 2 I have illustrated one method of accomplishing this result. Two cathode elements are represented schematically at F and F and may have a centre tap or common point if desired.- The two elements are supplied with current from an alternating current source by means of a step-down transformer having primary winding L and secondary windings L and L both closely coupled to the primary and each supplying current to one cathode element. A large choke coil L is connected in series with one cathode element and its secondary winding, in order to retard that current by approximately 90". A capacity may, of course, be used instead of a choke coil, in order to make one current lead by 90. Rheostats R0 may also be employed in order to control or equalize the currents.

Figure 3 illustrates another suitable arrangement for supplying currents which are out of phase. The cathode elements are shown at F and F as before and may, for example, be shunted by resistances or other impedances Z, providing a centre-tap arrangement. A transformer having a core C is provided with a primary winding L connected to an alternating .current source and a secondary winding L closely coupled to the primary. The secondary winding L is loosely coupled to the' primary, which may be accomplished by constructing the core with a magnetic shunt S, as shown. The currents supplied by the windings L and L will then be out of phase with each other, and the phase difference may be brought to approximately 90, or other desired amount, by properly proportioning the transformer windings and core. Rheostats R0 may be used as before, for equalizing the currents.

Instead of employing a centre tap arrangement in which the grid and plate circuits have a common connection, as illustrated in the foregoing figures, other arrangements may be employed. For example, the plate circuit may be returned to one terminal of the cathode, as illustrated in Fig. 4. In this case the tube 1 is provided with plate P, grid G, and cathode F, the cathode terminals 3 and 4 being shunted by a suitable im edance Z, for example a resistance. The p ate return through the plate impedance Z is connected to the cathode terminal 4, and the hum due to this connection is com ensated by displacing the grid return slig tly to one side of the midpoint of the shunt impedance Z, as by means of thetap 5. A practical advantage of this arrangement is that it permits a reduced number of leads from the tube.

Figure 5 shows a suitable connection for two tubes arranged in parallel. The principle explained above in connection with Figure 1, in which the cathode elements are lo-. cated in the same tube, applies equally to the arrangement of Figure 5, in which the oathode elements are located in separate tubes which are externally associated, as by the connections shown, or variations thereof, both of these arrangements being included in the term vacuum tube organization, as employed herein.

Many variations of the specific arrangements shown herein, fall, of course, within the scope ofthe present invention.

I claim:

1. An electrical network comprising a vacuum tube having a cathode system comprising a pair of filamentary elements, means for supplying said elements with alternating currents having a substantially quadrature relation, and a terminal conductively connected to the electrical mid-points of each of said elements, said terminal serving as a common terminal for the input and output circuits of said tube.

2. An electrical network comprising a vacuum tube having a cathode system comprlslng a pair of filamentary cathodes, sources of alternating current having a quadrature phase relationship, circuit elements for supplying the respective filamentary elements with current from said sources, and leads joining the electrical mid-point of each of said elements to a terminal, said terminal serving as a common terminal for the input and output circuits of said tube.

3. In an electrical network, a vacuum tube having input and output electrodes and a cathode system, said system comprising two filamentary elements, means for supplying said elements with alternating currents having a quadrature phase relation, a terminal and means establishing at said terminal the potentials existing at the electrical midpoints of each of said filamentary elements, said terminal serving as a common terminal for the input and output circuits of said tube.

4. The invention as set forth in claim 3, wherein said means comprises connections between said terminal and center taps on said filamentary elements.

5. The invention as set forth in claim 3, wherein said means comprises connections between said terminal and center taps on resistances shunted across the respective filamentary elements.

'6. A vacuum tube network comprising, in combination, a cathode system including a plurality of elements, a terminal conductive ly connected to the electrical mid-points of each of said elements, a source of alternating current supply, a transformer having a primary winding connected to said source and a plurality of secondary windings each connected to an element of said cathode system to supply current thereto, and means whereby the currents supplied to said cathode elements bear a predetermined hase relation.

7 A vacuum tube networ comprising, in

combination, a cathode system including at least two elements, a terminal conductivel connected to the electrical mid-points of eac of said elements, a source of alternating current supply, a transformer having a prlma winding and two secondary windings ea connected to an element of said cathode system to supply current thereto, one of said secondary winding? being closely coupled to said primary win 'ng and the'other of said secondary winding-s being closely coupled to said primary win 'ng, whereby the currents supphed to sald cathode elements bear a predetermined phase relation.

In testimony whereof, I aflix my signature.

STUART BALLANTINE.

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