US2835842A - Electric discharge tube - Google Patents

Description

y 20, 1958 H. A. WKTTEVEEN ELECTRIC DISCHARGE TUBE Filed March 18, 1952 INVENTOR Her-mun Adam WiHex/een United States PatentO ELECTRIC DISCHARGE TUBE Herman Adam Witteveen, Eindhoven, Netherlands, as-

signor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application March 18, 1952, Serial No. 277,103 Claims priority, application Netherlands April 13, 1951 2 Claims. (Cl. 313-239) This invention relates to an electric discharge tube. In particular, the invention relates to an electric discharge tube comprising a cathode which evaporates a conducting material and a plurality of connector pins sealed on a circular arc in a portion of the tube housing.

Tubes of the foregoing type, particularly small tubes, have a disadvantage in that metal evaporating from the cathode settles on the wall portion of the housing containing the connector pins to form a semi-conducting coating. This results in leakage current paths between the individual pins which impairs the operating characteristics of the tube.

It is an object of the invention to provide a novel construction for a tube of the foregoing type which avoids the disadvantages resulting from these leakage paths.

This and other objects of the invention will be best understood from the following description.

According to the invention, in an electric discharge tube having a cathode which evaporates a conducting or semi-conducting material and a plurality of connector pins sealed on a circular arc in a wall portion of a housing enclosing the tube, at least one insulating strip is supported by two substantially diametrically-opposed connector pins to overlie the inner surface of the wall portion containing the pins. The insulating strip prevents the evaporated conducting material from forming a conducting layer on a portion of the surface of the wall portion containing the connector pins lying under the strip and, consequently, prevents the formation of a continuous leakage path between the pins separated by this non-coated surface portion. This arrangement has the advantage that the same size insulating strips may be employed in all discharge tubes in which the connector pins are sealed on a circular are having the same diameter.

The two connectors pins which support the insulating strip are chosen to have the characteristics that current leakage between these pins will have slight effect on the operating characteristics of the tube because the evaporated conducting material will coat on the surface of the strip to form a leakage path. Where the discharge tube has a large number of connector pins, additional strips are provided to assure that the various pins are suitably insulated from each other.

The invention will now be described with reference to the accompanying drawings wherein:

Fig. 1 is a view, in cross-section, of one form of electric discharge tube in accodance with the invention;

Fig. 2 is a transverse sectional view of the tube shown in Fig. 1 on a plane above strip 14;

Fig. 3 is a view similar to Fig. 2 of another form of electric discharge tube according to the invention;

Fig. 4 is a view similar to Fig. 2 of still another form of electric discharge tube according to the invention;

Fig. 5 is a view similar to Fig. 2 of still another form of electric discharge tube according to the invention.

Referring to Fig. 1, an electric discharge tube comprises a housing sealed to a bottom wall portion 11. The housing 10' encloses an electrode assembly 12 ineluding a cathode 13 which evaporates a conducting material during operation and one or more other electrodes such as 16 which is connected to base pin 3. A plurality of connector pins 1 to 8 are arranged on a circular arc and sealed in the bottom wall portion 11 of the tube to provide external circuit connections for the various electrodes of the electrode assembly 12. Two insulating strips 14-, 15 are provided to prevent leakage between the various connector pins 1 to 8 resulting from metal vapor escaping from the lower end of the cathode 13 to form a semi-condutive coating on the bottom portion 11.

Referring to Fig. 2 which shows the connector pin arrangement for a combination diode-triode tube in one housing, the upper strip 14, which is preferably of mica, is arranged on two diametrically opposed pins 2 and 6 which are connected to the filament and the screen the filament pins, but such leakage will not impair the operating characteristics of the tube.

Furthermore, the leakage current will be small because the pins 2 and 6 are remote from. each other and because the very thin metal deposits generally have a high resistance.

Metal vapour does not deposit under the strip 14 and a portion of the bottom 11, consequently, remains entirely free from a conducting coating. Accordingly, the pins 1, 7 and 8 are satisfactorily insulated from the pins 2, 3, 4, 5 and 6. A second strip 15 may be arranged under strip 14 in order that leakage between the said pins may also be avoided. Since the strip 35 is covered in part by strip 14, a continuous leakage path is prevented from being formed across the surface. Even if the strips 14 and 15 lie in contact with one another, the sides of strip 14 ensures sufficiently satisfactory insulation since a deposit is not formed on these sides, which, in case of mica, are very rough. By placing two strips each on dilferent diametrically opposed pins, it is ensured that all the pins, except the pins 2 and 6, are satisfactorily insulated from each other in spite of the small relative spacing and the possibility that metal vapour may deposit on the bottom. Since the pins are located on the circumference of a circle, all the strips may be perfectly equal for any tube type having a bottom with which the diameter of the pin circle is identical.

Fig. 3 shows the invention being employed with the pin connections of a combination triode-hexode tube. In this case, one insulating strip is connected between pin 5 (hexode screen grids) and pin 1 (common filament), while the other strip is connected between pin 7 (common cathode) and pin 3 (triode anode).

The remaining pin connections are as follows: Pin 2 is connected to the hexode; pin 4 is connected to the triode grid and the third hexode grid; pin 6 is connected to the first hexode grid; pin 8-is connected to the filament.

Fig. 4 shows the pin connections for a miniature (7 pin base) diode-pentode in which one insulating strip is connected between the filament (f) and the screen grid (3 p The remaining pin connections are as follows: Kg is the pentode cathode and suppressor grid pin; d is the diode anode; g is the pentode control grid; a is the pentode anode; f is the common filament.

Fig. 5 shows the pin connections for a double pentode having 9 pins in which one strip is connected between the screen grids 3, 7 of each pentode unit. Although in this case the pins are not exactly diametrical, the strip still has the same length.

The remaining pin connections are as follows: pins 1 and 9 are the common filament; pins 2 and 8 are the anodes for each pentode unit; pins 4 and 6 are the control grid for each unit; pin 5 is the common cathode and suppressor grid connection.

In each of the above-described cases, the strip closest to the cathode is connected between a pair of pins having the characteristics that leakage current between them will have only a slight effect on the operation of the tube.

While we have thus described our invention with specir'ic examples and embodiments thereof, other modifications are readily apparent to those skilled in the art without departing from the spirit and the scope of the invention as defined in the appended claims.

What I claim is:

1. An electric discharge tube comprising an electrode assembly including a cathode which evaporates a con ductive material and at least one other electrode, a housing enclosing said electrode assembly and including a substantially flat base portion, a plurality of connector pins arranged in a circular are on and sealedin said base portion and connected to said cathode and said other electrode, respectively, to provide external circuit connections therefor, and at least two solid insulated strip-like members each supported by a different pair of substantially diametrically-opposed connector pins between said base portion and said electrode assembly and 4 overlying each other and the inner surface of said base portion to prevent leakage current between said connector pins, the strip-like member remote from the inner surface of said base portion being supported by two pins between which leakage current has only a slight effect on the operation of the tube.

2. An electric discharge tube as set forth in claim 1 in which the strip-like members are constituted of mica and extend approximately at right angles to one another.

References Cited in the file of this patent UNITED STATES PATENTS D. 135,792 Eitel et a1. June 8, 1943 1,639,805 McCullough Aug. 23, 1927 1,814,711 Kingdom July 14, 1931 2,087,327 McNally July 20, 1937 2,112,124 Teves Mar. 22, 1938 2,184,709 Bruijnes et al. Dec. 26, 1939 2,227,093 Laico Dec. 31, 1940 2,346,913 Depew Apr. 18, 1944 FOREIGN PATENTS 424,111 Great Britain Feb. 14, 1935 U. S. DEPARTMENT OF COMMERCE PATENT OFFICE C ERTIFIC ATE 0F C ORREC TION Herman Adam Witteveen s .in the printed specification tion and that the said Letters Patent No. 2,835,842 May 20, 1958 Column 1, line 4% for "comets-tors" read e connector line 61, for 'aceodence read me accordance g column 2 line 54, after 'he' xode and before the semi=colon insert ed anode e u Signed and sealed this 29th. day of July 1958.,

(SEAL) Attest:

KARL WINE ROBERT c. WATSON Comnissioner of Patents Attesting Officer

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