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Патент USA US2125105

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Patented July 26, 1938
Werner Espe, Berlin-Siemensstadt, Germany, as
signor to Siemens-Scliuckertwerke Aktienge
sellschaft, BerlimSiemensstadt, Germany, a
corporation of Germany
Application April 14, 1937, Serial No. 136,875
In Germany July 1, 1936
4 Claims. (01. 250-275)
This invention relates to cathodes and es
pecially to cathodes utilizing a large supply of
mediate spaces between the wires is rigidly held
against any damage from the exterior of the
electron emitting material.
cathode and due to the protecting wires, the igni
tion of va portion of the exterior coating ispre
An object of the invention is to provide a cath
5 ode containing a large supply of electron emit
ting material and yet one in which the electron
emitting material evaporates with
stability without the formation of ignition or
torch spots.
Other objects and advantages of the invention
will be apparent from the following description,
in which:
Figure l is a cross-sectional view through a
preferred form of a cathode constructed accord
ing to the invention;
Fig. 2 is a side elevational view of the wire net
work of Fig. 1;
Figs. 3 and 4 are cross-sectional views of mod
i?cations of Fig. l; and
Fig. 5 is a side view partly in elevation and
partly in cross-section of the fastening of the
lead to the cathode body.
One of the difficulties with the coated cathodes
of the prior art is that if a large quantity of
25 electron emitting material is utilized, the rate of
electron emission is apt to be very unstable.
Thereispresentthe danger of certain parts ignit
ing into a ?ame with the consequent destruction
of the cathode. Even if the cathode does not
30 ignite, yet there is danger of the cathode having
an unusually large emission beyond that desired
at ?rst due to the large amount of material pres
According to the present invention, the cathode
35 is constructed by providing a plurality of wires,
preferably parallel, as supporting cores for the
cathode construction. Each of these wires is
preferably individually wound with the spiral of
thin wire, and then, in addition, the whole as
40 sembly is preferably wound with a common wire
spiral which holds the whole bundle of wires to
gether. In this manner, a rigid wire network
is formed for the electron emissive material.
Since each of the core wires is individually Wound
45 with a thin spiral wire, hollow spaces result
which can hold a sufficiently large mass of oxides
or compounds which may be converted into
oxides. There are also intermediate spaces
through which the light metals resulting from
50 the oxides and effecting electron emission may
diffuse from the inner portion of the wire net
work to the surface of the cathode. These light
metals are generally barium and strontium from
the well known barium and strontium oxide coat~
55 ing. In particular, the oxide mass in the inter
For the core wires, a material is preferably
selected which combines a high speci?c resist
ance with a large rigidity so that the cathode
assembly does not bend under the influence of its
own weight at high temperatures. For the sup lo
porting core wires, material from the tungsten
group, such as tungsten or molybdenum, or an
alloy of both is preferable.
For the winding of
the individual core wires, a material is utilized ‘
to which the oxide mass sticks well, as, for ex 15
ample, copper, or any of the copper group of
metals. For the material of the wire for a com
mon winding of the bundle of cores, a material of
high solidity is particularly suitable, as nickel.
It is also preferable to provide an additional 20
wire within the oxide coating, and preferably in
the center of the core wires or adjacent thereto,
of one or more Wires of a material that exert
a reduction effect on the electron emitting coat
ing which is, of course, preferably of alkaline 25
earth oxides. This wire, which need not be in
conductive connection with the other wires, may
consist of some metal such. as magnesium or alu
minum. Due to the presence of this wire and
its effect upon the coating, an increase in ad 30
mission is obtained in a very simple manner.
The value of the heating current determines
the preferred number of core wires which are
preferably three or more. It is preferred that
wire material of the same thickness be utilized 35
for the different cathodes, to provide an exten
sive standardization in manufacture.
In Figure 1, the numeral l identi?es the core
wires while the thin wires 2 are individually
wound thereabout. Numeral 3 is the rigid wire 40
bindings by which the Whole bundle is held to
gether. The spaces It and 5 are ?lled with elec
tron emissive material previously mentioned.
This emissive material is pressed together and
held rigidly, especially in the space 4 between 45
the core wires. By reason of the winding of the
core wires, there are between them intermediate
spaces through which the electron emitting may
terial can in spite of its high compression travel
outwardly very freely. Fig. 2 shows the con 50
struction of the cathode in side elevation in
which the electron emissive material and a por-'
tion of the outer Winding are omitted to more
clearly illustrate the construction of the wire
Fig. 3 shows a modi?cation in which a wire 6 g
is embedded in the'oxide mass and this wire may
consist of a metal preferably aluminum. Be
tween the aluminum wire and the alkaline earth
oxide, a so-called alumino-thermic action takes
place whereby the emitting properties of the
cathode are very much improved.
Fig. 4 illustrates a further example in which
?ve core wires l are utilized in combination with
10 two aluminum wires 6. The number of wires
may be increased in any desired manner in ac
cordance with this relationship. In Figs. 3 and
4, the windings about the core wires are also
designated with the numeral 2 and. the common
15 winding of the wire bundle by the numeral 3.
The windings of the wires are made more nar
row at the terminals since the wires may be more
rigidly held together at this place. In Fig. 5,
the cathode conductor 1 is reduced to a pin 8
20 at its center which is thrust in between the core
wires I.
It is preferable to thrust the shell 9
the invention have high stability, good emission
properties and long life.
While in accordance with the patent statutes I
have disclosed preferred embodiments of my in
vention, it is apparent that many modi?cations
may be made without departing from the spirit
of my invention. Accordingly, I desire only such
limitations on the following claims as are neces
sitated by the prior art.
I claim as my invention:
1. A cathode for electron discharge devices
comprising a plurality of core Wires and a coat
ing of alkali earth material thereon, one of said
wires being of a material which exerts a reduc
tion e?ect on said alkali earth material.
2. A cathode for electron discharge devices
having heating current applied thereto compris
ing a plurality of supporting co-re wires, a wire
around each of said supporting core wires, a wire
surrounding both sets of wires and an electron 20
emitting material coating on said Wires.
over this connecting region. The shell is con
nected to the cathode or the cathode conductor at
3. A cathode for electron discharge devices
comprising a plurality of supporting core Wires,
the points I 0 and I I by welding.
a wire around each of said supporting core wires,
a wire surrounding both sets of Wires, an alkali 25
earth material coating on said wires and an addi
tional wire within the coating on said wires of
In place of this,
25 the outer winding of the wire bundle may be
continued over a predetermined length of the
lead wire or at the terminals a second winding
may be brought on which encloses the whole
wire to attain a high rigidity.
Further, it is advantageous not to cover the
terminals of the wires with alkaline earth oxide,
but instead the terminals may be coated with a
material which radiates heat poorly, such as,
for example, aluminum oxide.
The cathodes constructed in accordance with
a material which exerts a reduction effect on
said alkali earth material.
4. A cathode comprising a bundle of longi 30
tudinally extending wires and a connector for
one end thereof, said connector having a pointed
projection inserted in said bundle and making
contact thereto.
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