US2052725A - Electron emission control arrangement - Google Patents

Description

I w. VAN B. ROBERTS ELECTRON EMISSION CONTROL ARRANGEMENT Sept. 1, 1936.

Filed July 11, 1932 INVENTOR WALTER VAN B- ROBERTS BY g ATTORNEY Patented Sept. 1, 1936 PATENT OFFICE ELECTRON EMISSION CONTROL ARRANGEMENT Walter van B. Roberts, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 11, 1932, Serial No. 621,772

4 Claims.

'The present invention relates to electron emission systems, and more particularly to an improved method of, and means for, reducing the time required to bring the cathodes of separately heated or indirectly energized, cathode tubes up to the temperature of electron emission.

The present practice in the operation of such tubes is to apply a fixed voltage to the heater or energizing element, which will be hereinafter called the filament. According to one embodiment of the present invention the voltage applied to the filament will be greater than its normal voltage from the time the voltage is first applied until the cathode has reached approximately its operating temperature whereupon the filament voltage is reduced to normal by the action of the electron stream from the cathode with the result that the time of over-voltage on the filament is made exactly the same as the length of time required to produce emission from the cathode.

Another embodiment of the invention consists in applying a voltage to the cathode itself for producing quick heating thereof and disconnecting this voltage as soon as emission begins, the disconnecting means being operated by the electron stream from the cathode itself; in this case the normal voltage being applied to the filament throughout.

Another object of the invention is to provide a tube which differs from an ordinary separately heated cathode type of tube in that two connections are brought out from the cathode, one from each end, so that a heating current can be caused to traverse the cathode.

' The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit arrangements whereby my invention may be carried into effect.

In the drawing,

Fig. 1 illustrates a conventional radio receiver which embodies the invention,

Fig. 2 illustrates a modification of the invention,

Fig. 3 is a cross-section of a tube designed to be used in the arrangement shown in Fig. 2.

Referring now, to Fig. 1 a conventional radio receiver is shown including a grounded antenna circuit A, coupled to a detector circuit provided with tube T, having a reproducer R in its anode circuit. This simple arrangement will serve to explain the invention, it being understood that radio frequency stages may precede the detector, and audio frequency stage or stages follow the latter. The plate supply of tube T is produced by rectifying alternating current in tube 20, and filtering it in a manner well known in the art through filter F. The filament of tube T is heated by voltage supplied by secondary 1 of the multi-winding power supply transformer M whose primary I is connected to the 110 volt alternating current source of voltage. The operation of this arrangement is as follows:

When the primary switch 9' is open and the tube T is cold, spring 3 holds the pivoted iron armature 2 up against contact 4, thus connecting the filament 2| tothe entire winding I which may be designed to deliver, for example, 4 volts. When the primary switch is closed four volts will then be applied to the filament thus causing a much more rapid heating of the cathode 22 than the normal voltage, for example, 2 volts. As soon as the cathode is hot enough to emit electrons a plate current will be established which fiows through relay winding I disposed in the positive lead of the filter F, and pulls armature 2 downwards away from contact 4 and against contact 8, thus connecting the filament to a portion only of winding 7 which gives the normal voltage such as 2 volts.

So long as the receiver continues in operation the fiow of plate current through relay I maintains the filament voltage normal. The reason why an abnormally high voltage may be impressed upon the filament during the heating up period without burning out the filament wires is that when the cathode is relatively cold, heat is radiated much more rapidly from the filament, and, hence, the filament does not get so hot as it would if the over-voltage were continued after the cathode had reached its approximate normal operating temperature. The amount of overvoltage which may be safely used will, of course, depend upon the structure of the tube, and is best determined by experiment for any given type of tube.

In Fig. 2 the operation is somewhat similar except that the voltage applied to the filament 6 from winding 1 is constant, while the cathode 5 itself is heated by means of winding 9 until the cathode has reached a temperature giving electron emission. When the tube T is cold, spring 3 pulls the pivoted armature 2 against contact 4, and thus connects the two ends of the cathode 5 to the terminals of winding 9 which gives sufficient voltage for rapid heating of the cathode. As

when the cathode reaches its operating temperature. Another difierence in Fig. 2 is that relay I also functions as a choke in the filter circuit F, thus employing an existing circuit element for the present invention. 7

Fig. 3 represents a type of tube construction, in cross-section, adapted for use as tube T of Fig. 2. The lines it represent the cross-section of a cylindrical plate while the dots ll represent the grid. Numeral 5 designates the cathode which is a thin metal tube coated with electron emitting material, and having a flange preferably provided around each end to distribute heating current more uniformly throughout the tube. These flanges or rings are illustrated by the black dots H2. The connection to the upper flange is made by a wire 38 passing from the stem of the tube around the outside of the plate structure.

The filament 6 is supported in the usual fashion inside the tube envelope 453, which is to say that it may be kept away from contact with the oathode by means of careful spacing, or by means of the usual spacer 6' of insulating material. It

' is a feature of the tube shown in Fig. 3 that in- .sulating'material of'relatively poor thermo-conductivity and high thermo-inertia such as porcelain may be used for the spacer 6, since the time of heating is made short by the temporary passage of current through the cathode, so that it is not necessary tohave a rapid transferof heat from the filament to the cathode.

1 Figs. 1 and 2 have been made extremely simple in order to facilitate the exposition of the invention but it will readily be understood that the invention is applicable to any kind of receiver employing any number of tubes, and that the relay may be actuated by the space current of one of these tubes or the combined space currents of a plurality of these tubes. It should be noted that in choosing the voltage applied to the cathode during pre-heating, or the over-voltage applied to the filament in case the arrangement of Fig. 1 is'used, that these voltages should not 'be so great that the cathodes come up to the operating temperature before the filament oi the rectifier tube is sufiiciently heated to produce a voltage on the plates ofthe receiver tubes, for otherwise the over-voltage would continue beyond the time the cathode reaches its operating temperature, and until the time when the rectifier and filter begin to develop a considerable voltage supply. If this should happen the danger of overheating the cathode,'or filament, is unnecessarily increased.

It should be understood that this invention is readily adapted for use in any system where immediate operation of the tubes are desired. For example, in centralized radio systems employing local microphone announcement circuits, it is desirable to have tube heating delay reduced to a minimum.

While I have indicated anddescribed several systems for carrying my invention into efiect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What is claimed is:

1. In a receiver, a tube of the indirectly heated cathode type, a source of heating energy, means for applying an initial over-voltage to the heating element of the tube, and means operated by the space current of the tube for reducing the heating of the element to normal, said source consisting of a rectifier followed by a filter circuit, and said second means being a relay whose winding is an element of the filter.

2. In combination with an electron discharge a 3. In a system as defined in claim 2, said first means being connections between 'said source and the cathode oi the tube,.said normal heating means comprising permanent connections between the cathode heater element and said source,

and said last means comprising an inductance element of the filter network.

4. In combination with a thermionic tube of the indirectly heated cathode type, a signal circuit coupled to the signal grid and cathode of the tube, a source of heating current, a heating circuit between the tube heater element and said source, a current conditioning network connected between said source and the cathode and anode of the tube, a second heating circuit connected between the cathode and said source and means disposed between the cathode and anode of the tube and responsive to the flow of space current through the tube for rendering the second heating circuit inoperative when the flow of space current 60

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