US2164913A - Indirectly heated cathode - Google Patents

Description

July 4, 1939 F. D. GOODCHILD INDIRECTLY HEATED CATHODE Filed OCt. 19, 1935 Fig. 1.

2 Sheets-Sheet 1 i'mi July 4, 1939. F. D. GOODCHILD INDIRECTLY HEATED CATHODE Filed Oct. 19, 1935 2 Sheets-Sheet 2 Fig. 4..

Fig. 3.

Patented July 4, 1939 INDIRECTLY HEATED CATHODE Frank Douglas Goodchild, London, England, as-

signor to Iinternationa 1 Claim.

This invention relates to indirectly heated cathodes for thermionic valves.

It is known to form a heater for an indirectly heated cathode in a thermionic valve by coating a straight filament with insulating material and then bending the filament into the shape required for insertion into the cathode, as, for example, by bending the filament into a number of loops which are inserted in a loose bundle into a metal tube of circular cross section which forms the cathode proper.

It is the object of this invention to form a heater which can be readily maintained in any specified arrangement and in which a given length of wire can be accommodated within less space than heretofore.

According to this invention a heater for an indirectly heated cathode of a thermionic valve is formed by separately covering a plurality of wires with insulating material, then placing the wires parallel and coating them with a second coating of insulating material and finally forming the multiple wire into the shape required for insertion into the cathode.

This construction enables a given length of heater wire to be inserted into a smaller space, and also enables the heater wire to be maintained in a specified arrangement after folding into shape so that it can readily be fitted to any particular form of cathode.

The invention will be better understood from the following description taken in conjunction with the accompanying drawings in which;

Figure 1 shows a heater for an indirectly heated cathode formed according to the invention from two wires, whilst Figs. 2 to 5 show various forms of cathode using a heater according to the invention.

In carrying out the invention tungsten wire is coated with'an insulating coating of, for example, aluminium oxide by any usual method such as spraying with or dipping it into a sludge of this material, which is afterwards dried to leave a coating of solid aluminium oxide. The coating is preferably not so thick as that applied when a single length of wire is to be folded to form the heater.

Two wires thus coated are then placed parallel to one another and again fed through the coating machine so that a second coating is formed over the two wires together, the finished product being of the same form as the well known twin bore lead covered cable. As an example, tungsten wire of .0018" (.046 mm.) is coated till its diameter is approximately .008.010 (.2-25 mm.). Two wires of this size are placed together and lightly coated until the maximum dimensions are .022" (.056 mm.) broad and .011"

i etandard Electric Corporation, New York, N. Y.

Application October 19, 1935, Serial No. 45,701 In Great Eritain March 6, 1935 thick. The twin wire is then folded into the form required to insert it into the oathode proper.

Figure 2 shows the manner in which the twin wire is folded into a bundle and disposed within a cylindrical cathode, whilst Fig. 1 shows one manner in which the twin wire may be folded into a flat zig-zag form for insertion into a cathode of flattened form. At the parts a where the twin wire is bent the insulating coating breaks away, in the same manner as it does at the bends of a single wire, but with the double wire it is clear that there will be less danger of short circuits between the exposed tips of the loops.

Figure 3 shows the flat zig-zag of Figure l inserted into a cathode of fiat rectangular shape.

With any form of cathode the two wires are cut at one end and there joined as shown at b, Fig. 3. The other ends c, d of the two wires are connected to suitable leads for the heating current which traverses one wire of the zig-zag and returns along the other wire.

A heater of cathode for insertion into a flattened form may be formed into a series of flat wire above referred to. Figure 5 shows a fiattened rectangular cathode into which has been inserted a zig-zag winding of a triple core wire. In this case the heating current enters by one outside wire 0 at one end of the zig-zag and leaves by the other outside wire d at the other end of the zig-zag, the wire 0 and d being joined in the middle wire at f and g respectively as shown.

What is claimed is:

An indirectly heated cathode for a thermionic Valve comprising an open-ended casing of rectangular cross section having a greater length than breadth, an insulated structure of width approximately the internal breadth of said cathode mounted in the interior thereof, said structure being lated cores composed of three separately insucovered as a unit to form a triple wire and folded into fiat zigzag form, each fold thereof consisting of two separate parts, each part comprising a single insulated body having a triple wire core, and means interconnecting the end of said triple wire core in series, whereby a single series conductor arrangement is provided.

FRANK DOUGLAS GOODCI-IILD.

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