Note: Descriptions are shown in the official language in which they were submitted.
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The present invention is directed to a getter
assembly for use in television picture tubes. More
particularly the present invention is directed to a
getter assembly which functions to minimize potentially
destructive electrical arc curr~ents in television
picture tubes.
The problem of electrical arcs and arc currents
in television picture tubes is well known and described
in detail in the prior art, for example U.S Patent
4,101,803 (1978). As noted in this patent and elsewhere
in the prior art, conductive coatings provided on the
inside and outside of the funnel portion of television
picture tubes constitute a large capacitor which filters
the high voltage which is applied to the screen of the
television picture tube. The inner conductive coating
is at the same potential as the screen and transmits the
scraen voltage to the neck of the picture tube where it is
applied, e.g., by spring contacts, to a high voltage anode
electrode at the forward part of the electron gun. The
~20 various electrodes in the electron gun are closely
spaced and at widely different electric p~tentials.
This circumstance, as is well known,results in arcing
between the electrodes in the event that foreign parti-
culate matter occurs in an inter-electrode space or if
there is an improperly spaced electrode. In the event
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of an arc, the filter capacitor formed by the conductive
coatings on the inside and outside portions of the
picture tube funnel dumps its enormous s~ored charge
within a few microseconds resultin~ in instantaneous
currents on the order of hundreds of amperes and higher
which can cause destruction of associated circuitry.
A known technique for reducing the magnitude
of the arc currents is to employ a resistive coating on
the inner surface o~ the picture tube funnel, e.g.,
composition containing metal oxide, e.g., iron oxide.
The resistivity of such coatings is relatively high,
on the order of 2,000 to 6,000 ohms per square, and
the arc current can be reduced on that account. However,
in the gettering of television picture tubes, as is known
to the art, a film of barium metal is deposited on
portions of the inner funnel surface overlying the
resistive coating and, at times, can provide a low
resistance path and essentially short circuit the
~ resistive coating.
: 20 It is accordingly an object of tha present
invention to provide a getter assembly which avoids
the deposition of a short circuit barium film.
Other objects will be apparent from the
following description and claims taken in conjunction
with the drawing wherein
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;
Figure 1 shows a tele~vision picture tube
having a getter in accordance wi.th the present
invention incorporated therein
Figures 2(a)-2(d) show representative elevation
- and plan views of the ~etter of the present in~ention
Figure 3 is a perspective view of the getter
support member of the present invention, and
Figure 4 illustrates the distribution of
getter mat~rial using a getter in accordance with
the present invention.
- With reference to Figure 1 of the drawing, a
television picture tube is indicated at I0 having a
glass funnel portion 12 joined to neck 14. An electron
gun assembly is schematically indicated at 16. An
outer conductive coating is provided at 18 and a resistive
inner conductive coating is provided at 20. A high
voltage is conventionally applied to the resistive
inner coating through anode button 22. The above-
noted inner and outer coatings constitute a filter
capacitor.
A getter assembly is provided as shown at
24 mou~ted on elongated metal spring member, or "antenna"
26 which is attached at 28 to electron gun 16 whereby a
path is provided for the transmission of the high voltage
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on resistive coating 20 to the electron gun 16. This
path is incidental to the main high voltage path which
is via snubber spring contact ~7. When the getter 24
of the present invention is "flashed" the vaporized
getter material, e.g., barium, is deposited in ~he
funnel portion 12 as indicated at 30 and bridges a
portion of resistive coating 20. If this "bridging"
coating of barium were to c~ntact the support member
32 of getter assembly 24, a short circuit of resistive
coating 20 would occur in the event of an arc condition.
However, in the practice of the present invention as
hereinaflter more fully described, the barium film 30
is not deposited in the resion 34 where the getter support
member 32 contacts resistive coating 20.
With reference to Figures 2(a)-2(d) the getter
assembly of the present invention comprises a cylindrical
getter container or receptacle 40 suitably made of
stainless steel having an upraised bottom portion 42
which forms an annular open top channel 44 in which is
pressed getter material 46 in the usual manner, e.g.,
for example 1000 mg. of 25% Ba~ 25% Al, 50% Ni exothermic
alloy yielding about 225 mg. of Ba on "flashing". The
side wall 48 which joins floor member 50 of channel 44
is substantially greater in height than upraised portion
42 with respect to floor member 50, e.g., 1.5 to 5 ~imes
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greater in height, preferably about 2 times greater
in height. Antenna mount 26 is joined to the floor
member 50 by spot welds at 52. Wire support member 60,
shown in perspective in Figure 3, and with reference to
Figures 2(a)-(d), comprises a length of small diameter,
e.g., 0.045 inch wire having for convenience a flattened
middle portion and having end portions 68, 71 both bent
inwardly toward each other. These end portions are bent
first downwardly and thenupwardly to form curved bases
70, 72. The wire support member 60 is arranged perpen-
dicularly to antenna support 26 and fastened at its
flattened midpoint 62 by a spot weld. The wire support
member 60 will thus depend downwardly from the bottom
of metal receptacle 40 with the curved bases 70, 72
entirely beneath the floor member 50 and spaced inwardly
from side wall member 48 toward the upraised portion 42,
preferably about midway between the side wall member 48
and upraised portion 42. On account of the above-described
configuration, upon "flashing" of getter material 46, the
vaporized metal wiIl not deposit in region 34 shown in
Figures 1 and 4 due to the substantially higher side
wall 48 and since region 34 is essentially "shadowed"
against the gletter material vapor by the flow member 50
of receptacle 40. Thus, the inwardly curved base `
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portions 70, 72 rest in resistive re~ion 34 spaced
from getter metal film 30.
By way of specific example a getter assembly
in accordance with the presPnt i~vention was made with
a container of 305 stainless stelel having an outer
diameter of 0.765 in. The height of the container
sides was 0.165 in., the width of the getter channel
floor was 0.238 and the height of the upraised center
portion was 0.076 in. The wire support was formed of
0.045 in. diameter 305 stainless steel wire and held
the floor of the getter eontainer 0.155 in. from the
inner surface of the picture tube when installed.
Getter material (25% Ba, 25% Al, 50% Ni) in the amount
of i,000 mg. was pressed in the channel of the getter.
Using getters of the above type in accordance
with the present invention arc current was reduced in
tests to about 60 amperes from about 600 amperes which
resulted when getters were used which did not have the
combination o~ high side walls and "shadowed" support
member.
In some applications, the height 77 of wire
support member 60 is reduced so that the bottom of
receptacle 40 is closer than usual (0.155 inch)
to the funnel portion of the picture tube, e.g., about
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(0.130 to 0.150 inch), in order to enchance the 'l~hadowing"
efect.
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