US2060678A - Electric discharge device - Google Patents

Description

Nov. 10, 1936. P. LE NZ ELECTRIC DISCHARGE DEVICE Filed Nov. 29, 1932 Fig.5.

I I I I u I I I I n 7.

Inventor: Paul Lenz,

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cam 00 5 Patented Nov. 10, 1936 UNITED STATES.

PATENT OFFICE ELECTRIC DISCHARGE DEVICE Paul Lenz, Berlin-Grunewald, Germany, assignor to General Electric Company, a corporation of New York 8 Claims.

The present invention relates to electric discharge devices, more especially to tubes of the hot cathode type.

In the case of hot cathode tubes, particularly those of the larger type provided with indirect heating, a comparatively long time is necessary to bring the cathode to the working temperature after switching on the heating current.

An object of the present invention is to reduce the time necessary for this purpose. This object is attained in brief, according to the present invention, by initially applying to the cathode a higher voltage or current than is normally used. When the working temperature of the cathode is reached or even before that time, if desired, the heating current automatically is reduced to the normal operating value. The improved operation not only offers the advantage that the heatingup time is considerably shortened over the prior art methods but also in the case of arc discharge tubes containing vapor or gas, the vapor pressure necessary for operation is more quickly attained. Different arrangements may be employed for carrying out this process and a few exemplary Q embodiments are shown in the drawing. Fig. 1 illustrates an application of the invention to a filament energizing circuit which includes a resistance, while Fig. 2 depicts the invention as applied to an alternating current circuit containing a transformer. Figs. 3 and 4 show further embodiments of the invention in connection with indirectly heated cathodes.

Referring to Fig. 1, numeral l designates the envelope of an electron discharge device containing a filament 2, an anode 3 and an electrostatic control member or grid 4. The filament 2 may constitute the cathode of the device or in the case of an indirectly heated cathode (not shown), may comprise the heater. The circuit for energizing the filament 2 includes a source 5 of direct current in series with a resistance 6. In this circuit, there is a starting switch I, also a switch 8 which controls a short circuit across a portion of the resistance. Switch 8 normally is closed, as indicated. In accordance with the present invention, there is also provided in this circuit, either in series or in shunt thereto so as to be energized by the same source of current 5 as energizes the filament 2, a time switch or relay 9, the armature of which is mechanically connected in any suitable manner to the switch 8. The purpose of this relay will be explained presently.

As stated hereinbefore, it is desirable in many cases, particularly in power tubes employing indirectly heated cathodes of large metal content,

to bring the filament up to the normal operating temperature as soon as possible, thereby minimizing the time during which the tube is unable to take the load. When the cathode is to be initially heated, the switch I is closed and current from the source 5 flows through the lefthand portion of resistance 8, through switch 8 and the filament, back to the source. The time device 9 is also energized. The amount of heating current flowing through filament 2 is determined by the energized portion of the resistance. This current exceeds the normal heating current so that the filament temperature increases rapidly. The time relay 9 which is energized simultaneously by the closing of the switch 1, opens the switch 8 after a predetermined time so that the righthand portion of the resistance 6 is inserted into the heating circuit, causing a decrease of heating current. It is apparent that the amount of overheating may be controlled accurately by the setting of the time relay and adjusting the position of the tap on the resistance 6.

In Fig. 2, the filament 2, which may also be a cathode or the heater of a cathode, is supplied with alternating current from a source ID through a transformer I l of a voltage step-up or 1:1 ratio type. A tap may be brought out from one of the turns on the transformer primary to a contact 12 disposed adjacent to a contact l3. The latter is connected to an end terminal of the primary winding. There is a pivotally mounted armature I4 which moves between these contacts, said armature being connected to a source of current l0 through a switch 1. A time relay 9 is connected across the energizing circuit as in Fig. l, and the armature of the relay is mechanically connected in any suitable manner to the armature I4. It is apparent that as the switch 1 is closed with the armature in its upper position as shown, i. e. against the contact I2, the turn ratio of the transformer H is determined by the number of turns between the tap and the upper end of the primary. In the case of step-up voltage ratio, a voltage is obtained across the secondary, hence applied to the filament 2, which is greater under these conditions than if the armature M were making contact with the contact l3. The time relay 9 is also energized simultaneously when the switch I is closed. This relay operates after a predetermined time interval to cause the armature to drop back and strike the contact l3. The number of turns in the primary of the transformer l l is thus increased and the transformation ratio correspondingly decreased so that the voltage applied to the filament is reduced. As explained in connection with Fig. 1, the amount of overheating and the time duration may be controlled by the setting of the time relay, and in the case of a transformer coupling, by the proper determination of the tap position on the primary winding. It is apparent that in the case of a voltage step-down transformer, a tap may be brought out from the secondary winding instead of the primary winding and connected to a suitable arrangement of contacts. In all cases, the heating current is maintained above its normal value for a predetermined time interval and then automatically reduced to its normal value. If desired, both the primary and the secondary windings may have taps simultaneously controlled by suitably arranged armatures, actuated by a time relay.

Instead of the time relay, there may be employed a thermostatic relay responding directly to the temperature of the filament. The switching over from the greater heating current to the normal current then takes place, not after the expiration of a certain time, but after a predetermined rise in temperature of the filament or cathode. In this case, several tube constructions are possible. For example, there may be employed an additional filament which is the thermal duplicate of the filament 2 and which when heated in any suitable manner, operates a thermostatic switch for causing the required reduction of heating current supplied to the filament proper. Furthermore, the light given off by the main or duplicate filament may be directed onto a photo-electric tube or a thermo-electric element and cause the necessary switching-over of the heating current, using amplifying tubes, if necessary.

In the case of indirectly heated cathodes, the construction of the filament itself may be modilied to facilitate the heating-up process. Thus in Fig. 3 there is shown a metal cylinder l6 coated with electron-emitting material I! and containinga filamentary heater I8 securedat one end to the top of the cylinder. Leads are brought out from the free end of the filament, also from an intermediate tap, and from the cylinder I6. These leads are connected through relay contacts l2 and I3 to the source i0 in-the same manner as the leads from the primary of the transformer in Figure 2. During the preliminary heating-up period, current may be caused to fiow through the intermediate tap instead of the end terminal, the resistance of the filament being temporarily reduced in order to increase the current through the heater. After a time interval determined by a time relay, the connection to the intermediate tap is automatically broken and the entire length of the filament is connected to the energizing circuit, thereby reducing the current through the heater.

Fig. 4 shows the use of a plurality of filaments which may be operated in various ways to increase the initial heating-up of the cathode during the preliminary period. These filamentary heaters may have different or the same resistances and may be operated either separately or together under the control of a suitably arranged time relay so that any desired degree of current increase during the heating-up period may be obtained.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electron discharge device comprising a plurality of electrodes including a filament, means including a source of ourrent for initially applying to said filament a voltage greater than the normal operating voltage, and means including a relay energized by said source for reducing the voltage applied to said filament to the normal operating voltage, said relay having an inherent time delay characteristic and when energized, operating after a predetermined length of time depending on its inherent time delay characteristic to cause the said reduction of filament voltage.

2; In combination, an electron discharge device comprising a plurality of electrodes including a filament, a circuit for energizing the filament, said circuit including a source of current and a resistance, means including a relay having an inherent time delay characteristic in the energizing circuit for automatically changing the amount of resistance after an interval determined solely by the time delay characteristic of said relay whereby the voltage applied to the filament from said source is changed.

3. In combination, an electron discharge device comprising a plurality of electrodes including a filament, a circuit for energizing the filament, said circuit including a source of current and a resistance, said resistance being in series with the current source and filament, means including a relay having an inherent time delay characteristic in the energizing circuit for effectively removing a portion of said resistance during an interval determined solely by the time delay characteristic of said relay whereby the voltage applied by the current source to the filament may be held temporarily above the normal operating value and after said time interval is automatically reduced to the normal Value.

4. In combination, an electron discharge device comprising a plurality of electrodes including a filament, a circuit for energizing the filament, said circuit including a source of alternating current and a transformer, means including a relay having an inherent time delay characteristic in said circuit for changing the voltage ratio of the transformer, said means operating to provide a voltage across the filament greater than the normal voltage and after a predetermined time interval determined solely by the time delay characteristic of said relay, automatically to reduce the filament voltage to the normal value.

5. In combination, an electron discharge device comprising a plurality of electrodes including a filament, a circuit for energizing the filament, said circuit including a source of alternating current and a transformer having primary and secondary windings, relay means having an inherent time delay characteristic in the primary circuit for automatically changing the number of turns in the primary winding of the transformer after a predetermined time interval determined solely by the time delay characteristic of said relay means whereby the turn ratio of the transformer and the voltage applied to the filament are changed at a predetermined time after the filament is energized.

6. In combination, an electron discharge device comprising a plurality of electrodes including an indirectly heated cathode, a filamentary heater for said cathode, a circuit for energizing said filament, means including a relay having an inherent time delay characteristic and operating after a predetermined time interval determined by the said time delay characteristic for increasing the length and resistance of the heater whereby the heat given off by the heater is automaticaly reduced.

7. In combination, an electric discharge device comprising a plurality of electrodes including a filament, means including a source of electric energy for causing an initial flow of filament current greater than the normal operating current, and means including a relay energized by said source for reducing the current flowing in said filament to the normal operating current, said relay having an inherent time delay characteristic and when energized, operating after a predetermined length of time depending on its inherent time delay characteristic to cause the said reduction in filament current.

8. In combination, an electric discharge device comprising a plurality of electrodes in cluding a filament circuit, means including a source of electric energy connected to said filament circuit, said means being so adapted and. arranged that an abnormal wattage is initially consumed in said filament circuit, and means including a relay energized by said source for reducing the wattage consumed in said filament circuit to the normal operating wattage, said relay having an inherent time delay characteristic and when energized, operating after a predetermined length of time depending on its inherent time delay characteristic to cause the said reduction of wattage consumed in said circuit.

PAUL LENZ.

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