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Патент USA US2108589

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Filed Sept. 7, 1934.
Patented Feb. 15, 193s‘
_/.:_’o_xID'E cs'rnoni‘ MORE PARTICULARLY
Hendrik Items, Eindhoven, ‘Netherlands, assignor
' to N. V. Philips’ Gloeilampenfabrieken, Eind
hoven, Netherlands
Application September 7, 1934, Serial No. 743,139
_ In. Germany September 14, ‘1933
4 Claims.
(Cl. 250-275)
The present invention relates to a novel cathode
construction for ‘discharge tubes, and more par
ticularly to ‘a cathode construction having a large
electron-emissive area. The cathode structure of
preferably of a core wire of a refractory metal, for
instance of tungsten, which is covered with a
coiled nickel wire whose adjacent turns are in
contact with each other.
During operation, the heating current passes 5
the invention is especially useful in gas-?lled dis
> charge'tubes, for instance, recti?er tubes, adapted
to handle large currents. -
To obtain a high efficiency cathode, its surface
is activated by providing it with a highly electron
emitting layer, usually with an oxide layer. In
such cathodes, when adapted to handle large cur
rents, a large amount of oxide is to be distributed
over a large surface area and the oxide must ?rmly
adhere to the surface of thebody carrying the
oxide layer. If such cathodes are notproperly
degasi?ed, the occluded gases liberated during the
operation of the tubesdeleteriously influence the
through one, more or all of the coiled wires, so
that the cathode structure is heated both directly
and indirectly.
The coils of the assembly can be degasi?ed
individually, or simultaneously e. g. by sending 10
a series current through all of them if the con
struction permits. After degasifying this results
in a compact large-surface area ‘cathode struc—
ture which gives excellent performance and long
'When used in a gas-?lled discharge device, for
instance in a recti?er tube, the gaseous ?lling
proper operation of the tube and also reduce the
may be either an inert gas, or a vapor or a mix
life of the cathode.
ture of the two.
My invention will be more clearly understood
'Various constructions have been already sug
gested to obtain in a comparatively compact form
such cathodes of large electron-emitting surface
For example, it has been proposed for such
by reference to the accompanying drawing.
Figure 1 is a view of a coiled wire cathode of
a construction very commonly used in present
day practice‘.
posed heating element, whereby the surface of
Fig. 2 is a schematic view showing one embodi 25
ment of the invention.
Fig. 3 is a top view of a discharge tube having
a cathode structure according to the invention;
the cylinders and of the radial walls was coated
with an oxide layer.‘ However, such and similar
discharge tube shown in Fig. 3.
“ purpose to form a cathode'of a system of con
centric cylinders which are interconnected by
radial‘ walls and provided with a centrally dis
structures have the drawback that it is difficult
to readily and completely degasify same.
Forvgas-?lled recti?er tubes adapted to handle
comparatively small currents, a construction has
been suggested in the patent to Dobben et al. No.
1,718,123, which provides for a cathode structure
comprising a core of refractory metal, for in
stance of tungsten, around which is wound a coiled
nickel wire, the adjoining turns of the-nickel wire
40 being in intimate contact with each other. The
whole cathode body is provided with a coating of
highly electron-emissive‘substance, for instance,
a coating of alkaline earth metal, which ?rmly
‘adheres to the nickel. Such a cathode can be
readily deprived of all occluded gases by passing a
Fig. 4 is a partly secticnized side view of the .
In Fig. 1 the core l consists of a refractory
metal, for instance tungsten, a coiled wire 2,
preferably of nickel, covering the core with closely
wound turns and ensuring a ?rm adherence of the
electron emitting layer to the cathode surface.
In Figure 2 the cathode coil l consists of a
coiled tungsten wire surrounded by a nickel wire,
the entire coil being provided with a surface coat
ing of a high electron-emitting substance, for
instance with barium oxide. The cathode coil is
provided with supply leads 2 and 3. Within the
coil I is disposed a second coil ll of a construction
similar to that of coil l and having a smaller di
ameter, the two coils being preferably concentric.
highly electron-emitting surface, which at the
One end of the coil 4 is connected at 5 with the
lead 2 of cathode coil l, whereas the other end
of coil t is provided with a separate lead 6. The
leads 2, 3 and 5 are sealed to the envelope of the a
discharge tube in known manner.
same time has the advantage of easy degasifying
obtainable with the construction of said prior
bulb l containing a cathode constituted by two
’ high-intensity heating current through same.
The present invention provides for a compact
cathode construction having a large area and
According to the invention, a plurality of coile
Wires are disposed within each other, preferably
concentrically; the individual wires consisting
In Figs. 3 and It a recti?er tube comprises a '
' concentrical coiled tungsten wires 2 and 3, which
are covered with a layer of emitting material ad
hering to an intermediary layer of nickel wire
wound with adjacent turns upon a tungsten core. 55
The coiled wires 2 and 3 are supported by a
common metal rod 4, and two separate rods 4',
4" welded to sector shaped plates of special alloy
5, 5’, 5" respectively, to which the lead wires
6, 6', 6"are welded in their turn. The plates
5, 5’, 5" are hermetically sealed to the glass bulb
of the recti?er tube and through glass to each
other, for instance in the manner described in the
U. S. Patent #1334509.
The rods 4, 4’,'4i’~arlLsurrounded by porcelain
tubes 1, ‘l’, 1”, respectively, which tu
similar‘ni‘anner. Thereby each coil is preferably
connected‘with one of its ends to a common lead—
through which the discharge current passes dur
ing operation—and with its other end to individu
al leads and for degasifying, each coil is individu
ally heated during’ the, evacuation of the tube,
whereas in operation the heating current is sent
through an optional number of coils.
While I have described my inventionrorrhanwg‘”
of speci?c embodiments and specl?‘cma'ppli'c’ation, 10
glass sleeves 8, 8', 8", fused to the glass covering
'. ‘sh to be limjtedfthereto, but desire
the appended c - ~ t'p‘lle construed as broadly
the plates 6, 6’, 6", so as to form an absolutely
as permissible in view of the prior art.
tight protective layer, insulating the metal parts
15 of the leading in construction from each other
and from the discharge space.
. 7.»
Supported fromgaorcelain tube ‘I is a wire 9
>_,,d-/~‘/C9l1‘ryll1g a piece of a suitable getter material I0.
The wire is bent to a shape permitting the getter
20 to be retained in the position shown throughout
the pumping process, thus at a suflicient distance
from the incandescent cathode 2—3.
After the pumping process the piece of getter
material I0 is slipped over the upwardly bent
25 part of wire 9 and caused to drop to the coiled
part II in close proximity to the incandescent
cathode 2--3.
Then the getter material I0 is evaporated by
the heat generated by the cathode in order to
30 clean up'the tube.
At the bottom of the cathode bulb a mercury
container 23, ?lled with a small quantity of mer
cury, protrudes downwards from the cathode bulb
proper and serves to maintain the mercury vapor
35 pressure constant and at a value corresponding
to a temperature slightly above that of the sur
To the cathode bulb I are fused two arms I2,
each of which contains an anode I3 which is
40 screwed onto a rod I4, this rod being led through
the wall of the anode-arm by the intermediary of
a disc I5 in the manner set out above with rela
tion to the cathode construction of this tube.
The anodes I3 are closely surrounded by metal
45 gauze caps I 6, which con?ne the negative glow to
the front surface of the anodes I3.
The grids I‘! are provided closely to the anodes
l3 and consist of concentrical cylinders I8, I9
interconnected by radial partitions 20. This grid
50 construction is provided with an outside con
nection at 2| .
At 22 an auxiliary anode is provided in order
to improve the ignition conditions of the tube.
Referring to Fig. 2, the cathode coils I and 4
are degasi?ed during the exhaust of the tube by
their being heated individually to the proper tem
perature, whereby current is individually passed
through coils I and 4.
In the operation of the tube either pair of sup
60 ply wires 2-3 of 2-6 or both pairs may be used
for the passage of the heating current through
the respective coils. As a rule it su?ices to di
rectly heat either the outer coil I or the inner
coil 4, whereby the other coil is indirectly heated.
Normally the oxide layer provided on the coils
is su?icient to properly insulate them from each
other. However, if desired, insulating rods, indi
cated in the drawing by 'I and 8, for instance of
procelain, can be interposed between the coils.
It should be well understood that instead of
using only two coils so placed within each other,
the cathode structure can be formed of a larger
number of coils disposed within each other in a
What I claim is:
H.” -l m
1. A/"dischargee tube'coriiprising an envelope,
electrodes within said envelope including a cath
ode structure comprising a plurality of cylindri
cally-shaped coils concentrically-disposed in a
heat~retaining relationship, said coils being elec
trically interconnected and spaced apart to per
mit the discharge to readily reach both the in
ternal and'external surfaces of each coil, a layer
of a highly electron-emitting substance on the
surface of said coils, and leads for supplying dis
charge current to all of said coils and for supply 25
ing heating current to only a portion of said coils,
the remaining portion of said coils being indi
rectly heated from the directly-heated coils.
2. A discharge tube comprising an envelope,
electrodes within said envelope including a cath
ode structure comprising a plurality of cylindri
cally-shaped coils disposed one within the other
in heat-retaining relationship, said coils being
spaced apart and having spaced turns to permit
the discharge to readily reach all portions of the
surfaces of all the coils, a layer of a highly
electron-emitting substance on the surface of
each coil, a lead for supplying cathode-heating
current and discharge current to said cathode
structure, said lead being connected to one end 40
of each coil, and heating current leads connected
to the free ends of a portion of said coils, the
remaining portion of the coils being indirectly
3. A discharge tube comprising an envelope, 45
electrodes within said envelope including a cath
ode structure comprising a plurality of cylindri
cally-shaped electrically-interconnected coils dis
posed one within the other in heat-retaining re
lationship, said coils being spaced apart and hav 50
ing spaced turns to permit the discharge to
readily reach all portions of the surface of each
coil, a layer of a highly electron-emitting sub
stance on the surface of said coils, and means
including leads within said envelope to supply
discharge current to all the coils and to directly
heat only a portion of said coils during the oper
ation of the tube, the remaining coils being indi
rectly heated.
4. A discharge tube comprising an envelope, an
anode, and a cathode structure comprising two
cylindrically-shaped coils disposed one within the
other in heat-retaining relationship, said coils be
ing spaced apart and having spaced turns to
allow the discharge to readily reach the entire
surface of both coils, a layer of a highly electron~
emitting substance upon said coils, a lead con
nected to one end of each of said coils, a heating
current lead connected to the free end of one
coil, and a degasifying-current lead connected to 70
the free end of the second coil.
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