Note: Descriptions are shown in the official language in which they were submitted.
PHN 8947
The invention relates to a cathode-ray tube.
A cathode-ray tube generally comprises an
envelope including a neck, a cone and a window portion,
an electrode system provided in the neck to generate at
least one electron beam, and a getter.
A generally used method of securing a getter
holder in a cathode~ray tube, for example a television
display tube, is that in which the getter holder is
secured to the electrode system by means of an elongate
resilient metal strip (antenna) and is then inserted
into the tube neck together with the electrGde system.
The metal strip is pre-bent so that the getter holder is
~ pressed against the wall of the cone. A disadvantage of
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this method is that the metal strip is resiliently press-
ing against the cone of the tube exerts a force on the
electrode system, which impedes an accurate positioning
and centring of the electrode system in the tube neck.
Such a connection presents problems in particular when
the tube comprises a resistive layer which is provided
20~ internally on the tube wall and which extends at least
from~the neck-cone transition into ~he neck. As dis-
closed in British Patent Specification 1,226,728, which
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issued on March 31, 1971 to Philips Electronics and
Associated Industries Limited, this layer serves to
25~ restrict the detrimental consequences of a possible elec-
ric flash-over in the tube on the electronic circuit of
the television receiver. These flash-overs mainly occur
between electrodes o~f the electrode system which are
situatea at a small distance from each other and which
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PHN 8947
are operated at very different potentials. In such a
flash-over, a capacitor which is formed by the conductive
inner and outer coatings o the cone discharges. The
discharge is associated with current intensities rising
very rapidly in time so that in particular semiconductor
components in the electronic circuit of the television
receiver can be damaged via inductive or capacitive coup-
lings. The current strength occurring in such a discharge
is reduced by the resistive layer so that the possibility
of damage to the electronic circuit is reduced. When such
a resistive layer is used in conjunction with a getter
holder which is secured to the electrode system by a
resilient metal connection strip, the resistive layer may -~
be short-circuited by the connection strip, and in the
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case of a possible elec~ric flash-over in the tube sliding
sparks can occur along the connection strip. The endeav-
oured operation of ths rssistive layer is then lost for
the greater part. In order to solve this problem, British
Patent Specification 1,226,728 proposes to secure the
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getter holder to a component which is located inside the
conical part of the tube~. The securing is carried out
prior to sealing the glass cone to the glass window. It
is then necessary to use~a getter which can withstand the
detrimental in1uence of gases and vapours during subse-
quent stsps in the manufacturing process of the tube.
It is an object of the invention to secure a
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getter in a cathoda-ray tube in a simple way so that there
; is no dirsct mschanical coupling between the electrode
system and the securing element of the ge~ter holder.
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PHN 8947
According ~o the present invention there is pro-
vided a cathode-ray tube comprising an envelope including
a neck, a cone and a window portion, an electrode system
provided in the neck to generate at least one electron
beam, a layer which extends over the inner surface of the
cone into the neck and of which at least the part extend-
ing :Erom the neck-cone transition into the neck consists
of an electric resistive material, and a getter which is
arranged inside the cone and which is supported by means
of an elongate resilient element, characterized in that
the resilient element has a resilient clamping member
which is clamped in the neck between the electrode system
and the neck-cone transition.
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The~invention is based on the recognition of the
fact that the part of the resistive layer effective for
~; the end in~view is mainly restricted to the part extending
in the neck of the tube. Therefore, a small distance
between the clamping member and the electrode system, or
; between the clamping member and contact springs of the
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20~ electrode system contacting the~tube wall, will suffice.
The~clamping member may have any desired shape
and in one embodiment consists of a metal band in the form
; of an open ring. In order to increase the friction
between the band provided in its place and the tube wall,
the~surface of the band contacting the tube wall may be
roughened,~if desired.
The present invention will now be described by
way of example with reference to the single figure of the
accompanying drawing which ls a broken-away perspective
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PHN 8947
view of a neck and a part of the cone of a cathode-ray
tube made in accordance with the invention.
The cathode-ray tube is a colour television dis-
play tube having a glass neck 1 and cone 2. The inner
wall of the tube is provided with a resistive layer 3
extending into the neck 1. The neck 1 comprises an elec~
trode system to generate three electron beams. For that
purpose the electrode system comprises three electron guns
each comprising a first electrode 4, a second electrode 5,
a third electrode 6 and a fourth electrode 7. The elec-
trodes 7 are secured to a centring sleeve 8 which is con-
nected electrically by means of contact springs 9 to the
part of the resistive layer 3 extending in the neck 1.
A getter 10 is secured, vla a resilient metal
strip 11, to an open ring band 12 clamped in the neck 1~
The distance between the ring band 12 and the place where
the contact springs 9 press against the resistive layer 3
is approximately 1.5 to 2 cm. The resistive layer 3 con-
SlStS of approximateLy I part~hy weight of graphite powder,
6 to 10 parts by weight of iron oxide powder (Fe2O3) and
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1.5 to 3 parts by weight of an inorganic binder, for
examplej potassium silicate or sodium silicate.
During operation of the tube the layer 3 and
hence~also each of the electrodes 7 are at a potential of
25 ;approximately 25 kV. Ths electrodes 6 are at a potential
of approxlmately 5 kV. In an;electric flash-over between
an electrode 7 and an electrode 6, the dynamic resistance
in the present example, that is the resistance defined as
the quotient of the high voltage and the current strength
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PHN 8947
maximally occurring in the case of an electric flash-over,
was approximately 200 Ohm.
The getter 10 can be assembled in the tube in a
simple manner. For that purpose the ring band 12 has two
eyelets 13 by means of which the ring band 12 can be slid
on the jaws of a pair of tongs. For inserting the ring
band 12 and the getter 10 connected thereto by the strip
11, the ends of the open ring band 12 are moved towards
each other by tensioning the tongs and the assembly 10, 11,
12 can be inserted into the tube neck 1. As soon as the
desired position of the ring band 12 has been reached, the
tongs are relaxed so that the ring band 12 is clamped in
the neck 1. The electrode system is then inserted into
the tube neck 1 and the tube is then sealed and evacuated
in the usual manner.
The ring band 12 may also be provided differ-
ently with means~ with which it can be accommodated on an
inserting apparatus. For example, instead of the eyelets
13, the ends of the open ring band 12 may be bent inwardly.
It is furthermore possible to use the ring band 12, or
another suitable clamping member, to support a further
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electrode, diaphragm or~lens element to influence the
electron beam~s) generated by the electrode system.
The invention is further not restricted to tubes
in which the electrodè system in the neck is connected to
the reslsti~e layer by means of contact springs. The
; ~ invention may also be applied to tubes in which the elec-
trode system is arranged in the neck of the tube so as to
be fully insulated from the resistive layer, for example,
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PHN 8947
tubes in which the part of the layer extending in the tube
neck also constitutes an accelerating electrode.
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