US1967513A - Electronic discharge tube - Google Patents

Description

M. PONTE ELECTRONIC DISCHARGE TUBE Filed Jan. 28, 1952 MAURICE PONTE INVENTOR ATTORN 5Y5 July 24, 1934.

Patented July 24, 1934 'DISGHARG'E 7 Mauri e "Ponte, Paris, France, .a'ssigno'r Lfa .Radiot'echniqn'e, Paris, France, a 'cdspamitn of France ;Application-January 28, 1932,"Serial, No.=589,389

-.In;-FranceFebruary 1?, 1931 IClaim. o1. 2502215 i This invention :is for a hot cathode .gasfill-ed rectifier. It has long been known that the potential at the terminals of a rectifier :tube comprisinga he'ate'd cathode and anode, submerged in an extremely high vacuum, increases in proportion as the output of current from the tube increases, in consequence of the cloud of electrons which surrounds the cathode and opposes the discharge of electrons from the Lcathode. It has also been long known that this potential may be considerably diminished and made practically independent of the output current by submerging the cathode and anode in a gas or a metallic vapor, the ions of which reduce the space charge due to the electron cloud.

In these tubes it is particularly advantageous to utilize a mercury vapor, and the best results are obtained with the present invention when .applied to hot cathode mercury vapor rectifiers, although the invention may also be applied to rectifier tubes filled with gases. These rectifiers are constituted by a hot cathode and'an anode placed in a tube or other envelope containing mercury and submerged in vacuum. It has been found that when the cathodes of these rectifiers are heated in the normal manner whilst the tube is subjected to the rectifying potential, a particularly objectionable phenomenon is produced which often causes the deterioration of the cathode and renders it inactive after a few uses. If the supply of heating current to the cathode of a mercury rectifier is initiated while a rectifying potential is applied to the anode which effects the supply of current by the rectifier to the apparatus with which the rectifier is incorporated, the least irregularity of the cathode creating at any point thereof a relatively larger cathodic emission will have for effect that as soon as this point is raised to the emitting temperature, a rectified current originating at this point will pass through the rectifier and the whole output of rectified current will pass through this point which will be carried to an extremely high temperature, there.

being no possibility of limiting the current in these particular gas rectifiers. This causes the emitting substance of the cathode to be volatilized at the point in question, the phenomenon .having the appearance of a small are which passes from one point to another of the cathode, so that the latter is sometimes traversed upon the initiation of a rectifying operation under tension by an are or point of current concentration which grooves the cathode, leaving a path thereon deprived of emitting substance. eAfterisevleral repetitions of this :phenomenon the 'oaithode is seriously deteriorated. This is-the reason why inia, rectifier tube constructed an the 'manner. described, the cathode should be supplied with heating current at its normal load for at least a certain time, varying from, approximately, 15 seconds to several minutes before the anodic potential is applied.

Theundesirable phenomena above described are considerably reduced and often completely eliminated according to this invention by surrounding the cathode with at protecting grid electrically connected to the filament or element which forms the cathode. In this way, the field which is-formed around the cathode exactly at the. moment when the heating thereof is initiated, is diminished, and, at the same time it is distributed more uniformly. Also, the necessity of starting the rectifying action in the gradual manner above described is eliminated. The employment of a grid is preferable to that of a solid metal cylinder surrounding the cathode'as, to be efficient, the cylinder must be placed comparatively near to the cathode which causes the production of a high density of current prejudicial to a long life of the cathode and to obtaining a high resistance with reversed potential in the rectifying action. It is preferable that the ionization of the gas is distributed over the whole of the free space of the tube and the use of a solid cylinder is not advantageous from this point of view, particularly with cathodes which are not equi-potential, the current having a tendency to be localized at the points which are nearest to the anode. Moreover, the solid cylinder forms a reflector for the heat coming from the cathode; if account be taken of this gain of energy for calculating the form of the cathode, the system will be found to possess a considerable calorific inertia practically preventing the heating up of the cathode under potential and, if this gain is ignored, the cathode is heated too much in permanent load, which is prejudicial to a long life.

The essential charactertistics of the invention will be better understood by referring to the accompanying drawing which illustrates an example of the manner in which the invention is to be carried into effect. Fig. 1 of the drawing represents diagrammatically a hot cathode mercury rectifier tube. Fig. 2 is a plain view of a grid cap of the same tube. The cathode is shown in the form of a flat helically wound band 1 arranged to be heated by current en-- tering the bulb by the conductor leads 3, 4; an anode 2 is situated at the top of the bulb 7, which latter contains a drop of mercury 9. The actual improvement according to the invention is constituted by a grid 5 which surrounds the cathode and is electrically connected thereto by a connector 6. The grid is combined with a cap 8 which constitutes a screen between the cathode and anode. cal winding of the cathode is wound on a mandrel of 3 m/m diameter, the grid 5 .consists'of a helix of 0.7 m/m pitch and 10 m/m diameter, these figures being given as non-restrictive examples to this particular case. With this construction of rectifier, heating of the cathode whilst subjected to rectifying potential results in an initial action which is extremely regular as" long as the maximum load which the cathode can withstand is not exceeded, for example, 0.5 amps. with 12 watts heating current for an alkaline earth oxide cathode, these figures not being limitative of the invention but referring to this particular application. The ionization is uniformly distributed in thewhole of the bulb and IQ: 'I

As an example, the helithe rectifiers consequently give stable operation rendered certain by having said screen connected directly to the cathode so as to form an auxiliary portion thereof.

The invention has been more particularly described with reference to mercury vapor rectifiers, but it is clearly applicable to all gas-filled rectifiers such as rectifiers filled with rare gases.

I claim:

. A gas-filled electronic diode rectifier which comprises in combination a cathode, an anode, and a grid element in the form of an open screen surrounding the cathode and connected electrically to the said cathode by a direct connection the said grid being combined with a screen interposed'between the cathode and the anode.

MAURICE PONTE.)

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