US2123386A - Cathode construction - Google Patents

Description

July 12,- 193s.

- c. STANSBURY CATHODE CONSTRUCTION Original Filed March 20, 1933 Patented July 12, 1938 CATHODE CONSTRUCTION Carroll Stansbury, Wauwatosa, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Original application March 20, 1931, Serial No.

524,047. Divided and this application April 21, 1933, Serial No. 667,180

6 Claims.

Thisinvention relates to improvements in gaseous electron discharge tubes of the grid controlled type, this application being a division of my copending application No. 524,047, filed March 20,

The present application involves a novel construction of.a gaseous electron tube having an additional auxiliary electrode, which forms part of the system of the aforementioned application.

In the use of gaseous grid controlled electron discharge tubes it is often desirable to arrange for a unidirectional current flow in the grid circuit and when the source for supplying'the grid is alternating this necessitates employment of a rectifier to prevent the flow of current in the undesired direction.

.An object of the present invention is to provide a tube having means which obviate the necessity for employment of a separate rectifier.

Another object is to provide a unitary structure embodying a grid controlled gaseous electron discharge tube and a rectifier.

Another object is to provide such a unitary structure having a single cathode.

Another object is to provide a combined gaseous grid controlled electron discharge device and rectifier having a common cathode and separate anodes.

Another object is to provide a device of the aforementioned character in which the electron flow to one of the anodes is unaffected by variations of the grid potential.

Another object is to provide a device of the aforementioned character in which the effect of the grid upon the electron flow to one anode is unaffected by the flow of electrons to the other anode.

Various other objects and advantages will hereinafter appear.

The accompanying drawing illustrates my invention as applied to a system of control which forms the subject of my aforementioned application. It will be understood, however, that the invention is capable of various modifications, and that its use is not limited to the system illustrated.

Referring to the drawing, I is an electron tube which is preferably filled with a gas or vapor at low pressure. Enclosed in the tube is a filamentary cathode 2, which may be of a conventional type. The cathode is arranged with terminals by which it can be connected toa suitable source of electrical energy (not shown) for heating it to the desiredtemperature. A conventional anode 3 is mounted concentric with and at one end of the longitudinal axis of the cathode. The

cathode is surrounded by a preferably concentric cylindrical grid 4. This grid may be in the shape of a solid sheet completely enclosing the cathode except for an area at its upper end adjacent to the anode, of sufiicient extent to permit an unobstructed flow of the electron stream. Mounted in the space between the grid and the cathode is an auxiliary small anode 5.

It will be obvious that while the discharge between the cathode and the main anode 3 is subject to control by the grid no such control is exerted by the grid upon the discharge to the anode 5.,

Furthermore the discharge to the anode can have no appreciable effect upon the control efficiency of the grid relative to the main discharge or any appreciable effect upon the main discharge directly as long as the cathode is capable of supplying all of the electrons which are required by the two discharge currents and provided that the circuits of the two anodes outside of the tube do not affect each others impedance.

Due to the proximity of the cathode 2 to the auxiliary anode 5 the latter tends to heat up when the tube is in operation, such tendency being increased through shielding of the cathode 2 by the grid 4, which latter largely prevents heat radiation from the cathode. As a result, the space inside of the grid is heated to a relatively high temperature at which the anode 5 may tend to conduct current in the undesired direction. To prevent this, the anode 5 is preferably made of tantalum or a tantalum alloy whose surface is oxidized, as it has been found that such oxidized tantalum surfaces effectively prevent electron emission from a hot body and thus prevent the reversal of current in the circuit of the auxiliary anode 5.

Supply lines L and L impress alternating voltage upon the system. Cathode 2 is directly connected to line L while anode 3 is connected to line L in series with a translating device 6, the current of which is to be regulated. An adjustable condenser having plates of opposite polarity 8 and 9 is connected between the grid 4 and line L and is paralleled by an adjustable impedance II] which is preferably non-inductive. A transformer H has an adjustable primary winding [2 which is connected between the lines L and L and a secondary winding l3 which is connected between the grid 4 and the auxiliary anode 5.

The apparatus functions as follows:

When an alternating voltage is impressed upon the lines L L the cathode 2 becomes alternately negative and positive with respect to the anode 3, and if the grid has no voltage impressed upon it, current flows through the tube and the translating device 6 during the alternate half cycles when the cathode is negative. These alternate half cycles shall be designated as the working half cycles and the other half cycles the negative half cycles. An alternating 'voltage is also impressed upon the primary winding I2 of the transformer II, and the resultant current in said winding induces a corresponding voltage in the secondary winding l3. This secondary winding is so connected that its terminal which is connected to grid 4 is negative with respect to the auxiliary anode 5 during the negative half cycles of the main voltage, and thus a negative charge is accumulated on the plate 9 of the condenser during these half cycles, the charging current flowing from plate 9 through winding l3 to anode 5, cathode 2 and over line L to plate 8.

During the succeeding working half cycle, the polarity of the cathode and of the transformer winding reverses and the tube conducts current between the cathode 2 and the anode 3 if it is not prevented from so doing by a negative potential on the grid 4. However, since the impedance of the circuit of winding I3 is asymmetrical due to the unidirectional conduction between the cathode 2 and auxiliary anode 5, the negative charge on the condenser plate 9 cannot flow off through the anode 5, but only through the impedance I0 back to plate 8. By adjustment of this impedance it is possible to adjust the time which is necessary for the negative potential on plate 9 and grid 4 to reach a sufficiently low value to permit current flow between the cathode 2 and the anode 3, and it is thus also possible to adjust the moment during the working half cycle when the tube begins to supply current to the translating device 6. By varying this moment the effective current supplied to the translating device may thus be varied.

It will thus be seen that the auxiliary anode 5 in combination with the cathode 2 serves as a rectifier for the grid charging circuit, while at the same time the current which flows through this auxiliary circuit during the half cycles when no current flows between the cathode 2 and the anode 3, does not directly affect the current flowing between the main electrodes during the working half cycle.

It is obvious that the current supplied through the auxiliary anode may be used in various other ways besides the use shown herein, Where it is employed to charge a condenser, which in turn controls the grid potential.

What I claim as new and desire to secure by Letters Patent is:

1. A gaseous electron discharge tube having a cathode, an anode, a grid, these elements constituting a main rectifier and an auxiliary anode of an area which is negligible relative to the area of the grid and located in the space between said cathode and grid, said cathode and said auxiliary anode constituting an auxiliary rectifier to function independently of said grid.

"2. A gaseous electron discharge tube having a cathode, an anode, a grid surrounding said cathode, these elements constituting a main rectifier and an auxiliary anode of an area which is negligible relative to the area of the grid and located outside of the influence of said grid in the space between the latter and the cathode, said cathode and said auxiliary anode constituting an auxiliary rectifier to function independently of said grid.

3. A gaseous electron discharge tube having a cathode, an anode, a grid surrounding said cathode, these elements constituting a main rectifier and an auxiliary anode of an area which is negligible relative to the area of the grid and located within said grid, at a point outside of the main discharge path, so as to be unaffected by the discharge current between the cathode and anode, said cathode and said auxiliary anode constituting an auxiliary rectifier to function independently of said grid.

4. A gaseous electron discharge tube having a cathode, an anode, a grid in the form of a solid sheet enclosing said cathode, except for a discharge area adjacent to the anode, and an auxiliary anode located adjacent to said cathode and within said grid.

5. A gaseous electron discharge tube having a cathode, an anode, a grid for controlling the current flow between said cathode and anode, these elements constituting a main rectifier and an auxiliary anode having an oxidized tantalum surface, said cathode and said auxiliary anode constituting an auxiliary rectifier to function independently of said grid.

6. A gaseous electron discharge tube having a cathode, an anode and a grid surrounding said cathode, these elements constituing a main rectifier and an auxiliary anode located in the space between said cathode and grid, said cathode and said auxiliary anodev constituting an auxiliary rectifier to function independently of said grid.

CARROLL STANSBURY.

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