US2011922A - Discharge tube - Google Patents

Description

Aug. 1935- q J. R. H. VON WEDEL 2,011,922

DI SCHARGE TUBE Filed Feb. 25, 1931 ['31 Civil/Elma Wade! BY W, Hoax u 1 79d 14 g INVENTOR ATTORNEYS Patented Aug. 20, 1935 I UNITED STATES PATENT OFFICE DISCHARGE TUBE Carl J. It. H. von Wedel, Newark, N. J., assignor to Electrons, Inc., a corporation of Delaware Application February 25, 1931, Serial No. 518,068

7 3 Claims. (Cl. 25027.5)

This invention relates to discharge tube appersistent audible hum is introduced into the paratus, and is applicable to both gas filled and tube circuits which seriously interferes with thermionic tubes. reproduction and impairs the reception of sig- An object of the invention is to provide suitnals.

able discharge tubes which will be stable and It is the usual practice in the art to make the dependable under operating conditions, and which cathode sleeves of nickel, or other metal or alloy, will be eflicient and permit of accurate control the principal considerations of which are that of the operation and output of the tubes. they should have good electrical conductivity Fig. 1 of the drawing is a sectional view of or low resistivity to give a unipotential surface a thermionic tube embodying the invention, and one which will not interfere with the alka- 10 Fig. 2 is a view of the cathode assembly of line earth coatings thereon. In the present inthe tube of Fig. 1, and vention, however, I make the cathode sleeve of Fig. 3 shows the invention applied to a rectian alloy, the principal consideration of which fier tube of the gas filled type. is that it must have a very high magnetic per- 5 Anelectrode construction similar to that shown meability such that it effectively prevents the in Figs. 1 and 2, especially the heater element alternating fields induced by the filament heatand its relation to the cathode sleeve, is dising current from passing the sleeve, and thereby closed and claimed in my copending application, prevents electromagnetic and electrostatic fields ial N r filed ber 28, 1927. from being set up about the cathode, which other- Fig. 1 shows a thermionic tube of the indirect wise would aiiect the electron field between the 20 ea d yp having a b fi eating filament cathode and anode and cause hum in the tube I, heatable cathode sleeve 2, grid 3, and plate 4. circuits.

The filament or heater is supported by ceramic I have found that alloys of nickel and iron of insulator P s 5, and has terminals 8 for confrom 70 to 85 percent nickel and 15 to 30 percent nection to a source M of 60 cycle alternating iron have a sufilciently high magnetic permecurrent for hea in the fil m T asseme ability and are suitable for such a sleeve, and

' y is rigidly Supported y a Wire embedded will effectively prevent the alternating current i h glass press l5 of the tube. The energy hum, an alloy of 80 percent nickel and 20 pery the filament heats the cathode cent iron being particularly effective in this resleeve causing t same t become eleetrenieelly spect. It has also been found that the addition 30 emissive, the l v Preferably h vin a coating of .a small amount of cobalt to the above alloy of an oxide of the alkaline earth metals in order may b d irable for certain structural purposes. to increase ts emiSSivity- The filament i8 P These alloys are such that their magnetic pere eb y twisted hence-11y Wound S0 the meability is many times greater than the materesulting electric field about the filament is in rials heretofore used in the cathode sleeves- 35 e fo o a p in which case the total Space being much higher even than nickel, cobalt or c g distribution with respect 130 the Plate transformer steel, while their resistivity to ourfield will be much less affected than in the case rent flow is t correspondingly increased, of the bifilar fi e t having straig t p The resistivity of the alloy is important in that 40 tions. the electromagnetic forces are largely trans- 40 I Such tllbe y Variation deflection of formed into eddy currents set up in the sleeve.

the electron St ea from the cathode, any That resistivity is a factor is shown by the formuchan i the normal Sp charge about the la for the current density as determined by the h causes p ding changes to ccu solution of Maxwells differential equations of an inth Plate circuit of the tube- Theref0re,while electromagnetic field. In a massive conductor 45 the use Of alte t m' heating the eddy currents set up are a function of ments is desirable for many reasons, it causes serlous disturbances in the tube because the vary-i lie ing current sets up varying electromagnetic and electrostatic fields which interfere with the space where f is the frequency of the wave, u the percharge about the cathode and vary the electron meability and o the resistivity. However, even stream between the ca hod and pl Wh e though the material may have twice as much a 6 cyc e pp y current is used the e e c eresistivity, if it has fifty times more permeability, ated in the tube disturbances of both and the effect is that the electromagnetic forces emcycles, and these frequencies are such that a anating from the heater are five times more efu fectively neutralized or barred from the space charge in the tube, and the fact that the electromagnetic forces may introduce more heat in the sleeve due to increased resistivity is beneficial rather than detrimental, since it tends to maintain the necessary temperature of the sleeve. The low resistivity or high conductivity of the material has heretofore been considered the most important factor, whereas it is possible to increase the resistivity provided there is a much greater increasein the magnetic permeability, and still obtain a much better effect.

As shown in Figs. 1 and 2 of the drawing, the sleeve may be used as a core for the emissive coating of the cathode, but in other cases it may be desirable to provide a plating of nickel on the surface of the sleeve, which plating is preferably very dense and smoothly polished and thereafter oxidized and again reduced to obtain high, emissivity. Tubes made in accordance with this invention, and used as cascade amplifiers for audio frequencies, will permit an amplification of the signals up to many thousand times without an objectionable amount of hum being introduced by the heater field which formerly limited their employment for high amplification.

The invention may be advantageously employed in other kinds of tubes, such as gas filled discharge tubes operating from alternating current, and where it is necessary that fields created by electrodes having varying current impressed thereon will be restricted to certain areas in order to prevent interference with the main discharge of the tube.

Fig. 3 shows a gas filled discharge tube adapted for full wave rectification, having anodes 8 and 9 with a common filament l0 cooperating therewith, the electrodes being separated by barriers II which are preferably placed adjacent the anodes within the mean free path of the gas which fills the tube so as to prevent interaction between the plates and their barriers. The barriers have openings as indicated at l2 through which the main discharge passes. The tube is preferablyfilled with an inert gas, such as argon, but any suitable gas may be employed, and it has been found that the addition of mercury vapor to the argon is advantageous under certain conditions.

The barriers in such a tube shield the action of the field of one plate from the other plate field, and each of the plate fields should only extend efi'ectively towards the cathode. In this construction if the barriers are made of an alloy in accordance with the invention, the high permeability provides a more effective isolation of the respective fields, and enables the mass of the barriers to be considerably reduced which means more shock proof construction of the tube.

render the oxides less emissive.

Such barriers also have less gas content and are more readily degassed. Also, the large thin surfaces of such barriers may be more easily heated during the manufacturing process for purpous of degassing, because they will heat up earlier under eddy current treatment on account of their high permeability, and have the advantage of not corroding as easily as iron and have no large amounts of nitrogen occluded such as carbon, which is particularly difiicult to degas. Furthermore, the alloys will not interact with the oxide coated cathodes, even if they disintegrate to a certain extent under ionic bombardment, so as to They can be employed effectively in large mercury arc rectifiers, instead of the usual iron barriers around the anodes, because they will withstand mercury vapor.

In case it is desirable to prevent electromagnetic waves set up outside the tube from affecting the discharge path within the tube, the foregoing alloys of high permeability may be helically wound in the form of ribbons or wires around the discharge chamber and will provide an effective barrier with a minimum amount of material.

What I claim is:--

1. A gaseous rectifier tube comprising an electron emissive cathode adapted to be heated by alternating current, a plurality of anodes in said tube, and shields therein interposed between said electrodes, each at a distance within the mean free path of the gas from its respective anode composed of an alloy having a permeability several times higher than that of soft iron, for preventing the electromagnetic field about said cathode, due to the heating current, from interfering with the normal electron field between each shield and its respective anode and between said anodes.

2. A discharge tube comprising an electron emissive cathode adapted to be heated by alternating current, a cooperating anode, and a barrier surrounding said cathode and having a portion disposed between the cathode and anode, said barrier being composed of an alloy having several times higher magnetic permeability than soft iron for neutralizing the resulting field of the cathode in the space between the barrier and anode.

3. A discharge tube comprising an electron emissive cathode adapted to be heated by alternating current, a cooperating anode, and a nickeliron alloy barrier disposed between said cathode and anode, said barrier having a ratio of magnetic permeability to electrical resistivity several times that of soft iron and adapted to restrict the magnetic field of the cathode to the space between said cathode and barrier.

CARL J. H. VON WEDEL.

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