US1838888A - Incandescent cathode discharge tube - Google Patents

Description

1931- K. M. VAN GESSEL 1,838,888

INCANDESCENT CATHODE DISCHARGE TUBE Filed May 28, 1927 INVENTOR KAREL M.VAN GESSEL %4 glw/a A TORNEY Patented Dec. 29, 1931 UNITED j 5mm PATENT OFFICE KARIEL MARIN US VAN GEssE F.EINDHOVEN,,NETHERLAND'S, Assmma To mm CORPGRATION or .AMnnroA, VA CORPORATION or DEL W RE INCANIDESGENT YCLBI'IHODE DISCHARGE TUBE a lication fi-ledgMay as, 1927, Serial no. 194, 924, and "in the Netherlands June 8', 1926.

The present invention relates to incandescentcath'ode discharge tubes and has for its object a particular cathode arrangement which may beadvantageous in certainfcases.

\With certain types of cathodes or in particular those required to yield a definite emission at a given potential and strength of current, the wire is so long sometimes that it it is stretched out to its full length it canie not be introduced across the neck of the bulb. If on the other hand the wire is bent over in a V-shaped or hairpin-shaped manner, the effective length of the cathode is too short as in that case at each point of attachment or support a length of 4 to 5 millemetres, is lost for the emission because the heat is conducted away and only two short pieces in the middle are heated enough to emit electrons,

According to the invention, the cathode. '20 is constructed of two or more pieces of unequal length connected in series. The longer piece only takes an active part in the. emis sion, whereas the shorter piece, or pieces as the case may be, practically do not em1t because the heat is conducted away alongthe leads and supporting wires, r Q

In this case the latternon-emittingportions are preferably arranged outside the space enclosed by the anode and the grid so that only the effective portion of the cathode lies in this space and thereby a favorable V influence is exercised on the characteristics of the tube. V

A single example may serve for illustration: 7

A tungsten cathode coated with barium oxide must'have a length of about 30 millemetres for a current of 0.08 ampere, at a tension of 2 volts to heat the wire to incandescence. Now the greatest wire length which can be introduced in'a stretched state through the normal bulb neck of a receiving valve is some 24 millimetres; If the 30 millimetres wire is bent into a U or V shape and supported at the ends and in the middle, the length of the two emitting portions or the ellective length of wire is 2X (152 X 5) =10 millimetres because at each point of support 5 millimetres remain inactive by cooling:

nection is made i This length will hereinafter be'referred to i as useful length.

' If, according to the invention, one end of the wire is bent over for a length of '6 millimetres or, which is better, if the two ends are bent over for a length of 3 millemetres, so that the longer portion will liavea length of 24 millimetres the allowable length which can be introduced thru the bulb neck) the useful length metres. it i In the latter case'tliei usefu-l length is consequently 40% greater than in the first case so that the inclined portion of the characteristic curve of the tube resulting from plotting plate current against grid potential will be materially greaten f is then 24 2 X 5 14 milli- The ends of the wire may be bent over at.

right angles but with a flat construction of anode and grid. itis more advantageous to bend the said ends so as toproducea Z; 7

It is preferable that the non-emitting part of the cathode should beequally distributed at the two endsso that it would be immaterial how the polarity of the cathode terminals is chosen. "If. the non-emitting part isv not equally distributed at the ends, then the potential edifilerence between grid and cathode is dependent upon which end the grid con- If. the incandescent body consists of two parallel wires, it is possible for each of these wires to have one end bent over at rightangles and the two parts can be joinedso as to form an oblong rectangle'in which the leads engage @two oppositely disposed vertexes, or a single wire could be bent aroundfour supporting membersso-as to form a closed recg tangle with two of the supports serving as leads as in the former case. I J I The accompanying drawings show some embodiments of the invention. In the said drawingsz, V i i Figure (1 shows a stem supporting a single incandescent wire,.on e endot whichtakes no 'p'art in the emission.

H Figure 2 shows a stem with a flat arrange- V ment 'of anodeyand grid and with a sym-' metr cal construction of the single moan descent wire. c

Figure 3 shows a stem with two parallel incandescent wires joined by two inactive portions of wire forming a rectangle.

Referring to Fig. 1 the cathode consists of two portions 1 and 2, of which the greater portion 1 is arranged within the space enclosed by the anode 7 and the grid 6, at least in so far as the emitting part of the wire is concerned. As pointed out above, the heat is conducted away along the leads 3 and 5 and along the supporting wire 4 which carries the vertex of the cathode so that the temperature of the wire ends placed outside the just mentioned space is not sufficiently raised to impart to these ends an electronic emission of any importance.

In this unsymmetrical construction, the potential drop occurring in the portion 2 results in a material variation in the potential difference between the grid and cathode depending upon whether the grid 6 (if desired with the interposition of a biasing battery) is connected with the lead 5 or with the lead 3.

For this reason the constructions shown in Figures 2 and 3, in which there is symmetry, are to be preferred.

In the construction according to Figure 2 the incandescent wire consists of a long central piece 1 and two smaller pieces 2 and 12 of equal lengths which are sharply bent over so as to produce a Z. The portion 1 passes diagonally through the fiat substantially rectangular space enclosed by the anode 7 and the grid 6. The current is supplied along the leads 3 and 5 and the ends of the diagonal portion are supported by carriers 4 and 14: respectively. Theportion 1 is the longest straight length that can be slid through the bulb neck.

Figure 3 shows two wires similar to Figure 1 which are connected in parallel and which are united to form a rectangle. The current is supplied along the leads 3 and 5, and the two other vertexes are supported by carriers 4 and 14. The anode 7 and the grid 6 are the same construction as shown in Figure 2.

What I claim is:

1. A cathode for a discharge tube having the form of a rectangle, the portions of said cathode forming the longer sides of the rectangle being electron emitting portions, the shorter sides being resistances only, and leads to said cathode attached to diagonally opposite corners of the rectangle.

2. In a discharge tube, a cathode consisting of a pair of filaments connected in par allel, said filaments being in the form of a rectangle, a press having leads passing therethru connected to the ends of the filaments, and supports sealed in the press connected to points of the filament intermediate of'the leads, said supports engaging diagonally opposite corners of the filamentaryrectangle.

3. In an electron discharge tube having an anode, at least one grid and a cathode, said cathode having the form of an oblong rectangle comprising a plurality of emitting portions in parallel, said cathode portions each having non-emitting portions associated therewith serving as resistances only, the two narrow sides 0t said rectangle being arranged outside the space enclosed by the anode and the grid and leads engaging two oppositely disposed vertexes of said rectangle.

4. A cathode for a discharge tube having the form of a four-sided geometric figure, only one pair of opposite portions of said cathode being electron emitting, the other pair of opposite portions being resistances only, and leads attached to diagonally opposite corners of said four-sided cathode.

KAREL MARINU$ VAN GESSEL.

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