US2096249A - Electron discharge tube - Google Patents

Description

P. KAPTEYN ELECTRON DISCHARGE TUBE Oct; 19, 1937.

Original Filed 001;. 2, 1.951

ZOT-

Patented Oct. 19, 1937 UNITED STATES Y ELECTRON DISCHARGE TUBE Paul Kapteyn, Berlin, Germany Original application October .2, 1931, Serial No. 566,500. Divided and this application September 16, 1933, Serial No. 689,765. In Germany October 3, 1930 1 Claim. (01. 250-275) Various attempts have been made to perform the heating of the cathodes in the case of electrical discharge tubes having a control electrode, and more particularly electronic discharge tubes,

by alternating current. In particular cathodes of the indirectly heated type have acquired a certain significance in this connection. The direct heating of cathodes, however, by alternating cur rent has heretofore only been accomplished in incomplete fashion. The 'difliculties which are encountered in this connection are principally due to two conditions: 7

.In the first place the effective length of the filament varies with fluctuation in the heating current potential owing to the cooling action of the attachment ends, which action is all the more efiective the thinner the filament may happen to be (by reason of its correspondingly diminished heat capacity).

Secondly there is also a variation in the effective initial grid voltage of the particular stage concerned, since .the heating current potential constitutes part of the'efiective grid bias. The second difiiculty may be avoided by potentiometer arrangements which permit of a tapping of the effective potential zero.

Up to now the most favourable results have been obtained with cathodes requiring a heating current potential of approximately 1 volt. Filaments of less than 1 volt potential, however, are not capable of practical accomplishment, as the efiect of the cooling attachment wires is too great.

According now to the present invention, only that part of the filament is employed for the emission under control, the emission of which is relatively independent of the fluctuations in po- 7 tential of the total filament, and on which, therefore, the alternating potential responsible for the heating has no effect owing to its suflicient heat capacity in face of the poor discharge of heat.

Although up to now mention has only been made of fluctuations in the heating current potentials,

this of course applies only to relatively small fluctuations over extended cycles of time or greater fluctuations occurring in rapid succession, so that the fluctuation in temperature of the part of the filament in question is merely of an extremely low value, the rapidity of which is situated within the range of audible frequency.

Experiments have shown that the temperature in the case of fluctuations in the heating current potential remains practically constant by mission of the cooling attachment ends, and that the 55 small fluctuations in temperature still remaining stances, be impossible. cf the arrangement according to the invention v10 do not cause any variation in the effective length of the filament, and accordingly in the steepness and the amplification. Assuming, for example, that heating were performed with alternating current of 50 cycles, all of these variations would make themselves to such extent noticeable in the form of humming sounds in the anode circuit that faultless operation would, under certain circum- The practical execution may be performed in various manners.

A further object of my invention is a connection device directly supplied to the network and wherein the said electron discharge devices are used. 15

In the drawing illustrative of the invention,

Fig. 1 shows an electron discharge device which comprises an envelope A into which are sealed in r the usual manner an electron emitting cathode 2,

the attachment wires I, a cooperating anode 5 and. a discharge controlling grid 3. The devices shown in Figs. 24 are to be arranged in bulbs-in the same manner as shown in Fig. 1.

shows a circuit diagram of one embodiment of my Fig, 5

invention. 5.25

This application is a division of my application Serial No. 566,500 filed Oct. 2, 1931,

A possible form of embodiment is illustrated in Fig. 2. In this the attachment wires are designated l and the cathode 2. The control grid 4, 30 which surrounds only the middle portion of the filament 2, is constituted by a spirally wound wire, the ends 3 of which are disposed turn against turn and surround the remaining portion of the filament and, for example, a part of the 35 attachment wires I. 5 is the anode, between which and the control grid there is also provided, in theparticular embodiment shown, a screening grid 5, and in similar manner it is, of course,

also possible in the arrangement according to the 4:0

'nating heating potential, which'may amount, for

example, to one volt and may be taken through the medium of a transformer from a lighting network of cycles, is applied to the attachment ends I, the filament will possess at its ends very greatly fluctuating temperatures which will make themselves noticeable by fluctuation in the effective length of the filament. These fluctuations, 50 however, are, as stated above, practically confined I to the extreme ends of the filament, which are surrounded by the part 3 of the grid, and the emission of which is accordingly unable to pass through the meshes of the grid 4 to the anode 5.

In the case of a model actually constructed the length of the effective heating current potential amounted to approximately 0,3 V.

An additional form of embodiment of the invention is illustrated in Fig. 3. In the latter I designates the attachment wires of the filament 2, I 4 the controlgrid, and I5 the anode. In this case the anode is so short in relation to the length of the filament that the ends of the'filament subjected to the disturbing fluctuations in tempera.- ture are unable to assist in the emission to any appreciable extent. It is, of course, also possible to employ with advantage in similar fashion normal electrodes with correspondingly long filaments. I

In Fig. 4 there is shown a further form of embodiment of the invention. Theattachmentends I carry the filament 22, which only at its middle portion consists of a greatly emissive material or is treated accordingly. which for example, is disposed about the filament inconcentric fashion, and-25 is the anode. this case too the fluctuations in temperature at the ends of the filament are unable to take effect inthe form of a disturbing humming sound in the anode circuit, as the same play no part, or

only an extremely minorone, in the emission.

As stated above the source of heating current potential requires to be bridged by a potentiometer or equivalent arrangement, which permits of a point of constant potential, which is more'particularly necessary for the grid circuit in order to prevent fluctuations in the effective grid bias. 7

In Fig. 5 there is shown a circuit diagram of this kind. The figure shows a two-stage resistance-coupled amplifier, in which the amplifier valves are designated 1 and 8. The cathodes 9 and I0 thereof are fed by the lighting main through the mediumof a transformer H. The

anode circuits of the valves contain in the known manner a high ohmic resistance I2, and loud speaker I3 respectively. Coupling of thef'valves is performed over a condenser l6, while the initial grid voltage of source 18 is passed to the grid of the second valve over the high ohmic re- 24 is the control grid,

advantages of various kinds are obtained.

shown that this potentiometer resistance, particularly in the case of two-stage amplifiers, results .in a disturbing back coupling, because the same constitutes both a part of the anode circuit of the second stage as well as a part of the grid circuit of the first stage. It is only by'particularly suitable selection of the size of this potentiometer resistance that these back-coupling tendencies may be reducedto an acceptable degree. 1 V

Experiments have shown that the potentiometer resistances in a two-stage resistance-coupled amplifier should not exceed at the most 10 ohms assuming proper freedom from humming noises is to be obtained.

; The ideas of the invention as herein described are naturally notconfined to-the' described arrangements, but may be adapted on similar lines to numerous other arrangements.

It is,'of course, also possible toco-mbine several of the forms of embodiment described, whereby An electron" valve comprising a cath odeland other electrodes, preferably a control grid and an anode surrounding concentrically said cathode, said cathode being considerably longer than I said'electrodes for reducing the efiective emissive part of the cathode in order that no "disturbing variations of emission are produced by a1ternat-' ing heating potentials, ,said cathode consisting of a filament having a uniform cross-section the emission effective part of said filament being coated vrlth a highly emissive layer. r

PAUL KAPTEYN.

along the .Whole of. its length, only the middle for

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