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Патент USA US3082351

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March 19, 1963
A. w. COOLIDGE, JR
3,082,347
ELECTRIC DISCHARGE DEVICE UTILIZING NOVEL SEALING MEANS
Filed Dec. 11, 1959
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INVENTOR:
ARTHUR W.COOLIDGE,JR.
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HIS ATTORNEY.
United States Patent 0 "
1
3,082,347‘
Patented Mar. 19, V1 963
2
1
Another object of my invention is to provide a new
3,082,347
and improved sealing arrangement which enables and
Arthur William Coolidge, Jr., Scotia, N.Y., assignor to
facilitates the reworking of a defective envelope assem
bly and the reuse of component parts.
ELECTRIC DISCHARGE DEVICE UTILIZING
NOVEL SEALING MEANSv
General Electric Company, a corporation of New York
Filed Dec. 11, 1959, Ser. No. 858,956
9 Claims. (Cl. 313-250)
My invention relates to electric discharge devices and
pertains more particularly to improved envelope structures
therefor.
Another object of my invention is to provide a new
and improved ceramic-andmetal electric discharge device
envelope including improved anode sealing means.
Another object of my invention is to provide an im
proved ceramic-and-metal envelope structure ‘for an elec
10 tric discharge device incorporating improved means for
minimizing undesirable corona formations.
Still another object of my invention is to provide a
new and improved combined envelope seal and electrical
contact arrangement which minimizes transmission to the
in a desired manner and then placing the stacked assem
bly in a brazing furnace, thereby to bond the several ele 15 seals of any strain from electrode-supporting members
contained in the envelope.
ments to complete the envelope. Following ‘such an op
‘ Further objects and advantages of my invention will
eration the complete envelope is usually tested to detect
become apparent as the ‘following description proceeds and
leaks and when a leak is encountered it is generally neces
the vfeatures of novelty which characterize my invention
sary to discard or reconstruct the whole assembly. IFur
ther, in manufacturing a device in this manner the size 20 will be pointed out with particularity in the claims an
nexed to and forming part of this speci?cation.
of the available brazing furnace is a decided limitation on
In carrying out the objects of my invention I provide
the size of the envelope to 'be constructed. Still further,
an electric discharge device including a ceramic-and-metal
in ceramic and metal tube envelope constructions the
envelope containing at least a partially reduced atmos
metal sealing rings generally serve as electrical contacts
for electrodes contained in the envelope which require 25 phere and comprising a plurality of ceramic wall sections
each having bonded thereto a sealing ring. The sealing
the making of some electrical connections between the
ring provides a lap seal between it and the outer surface
sealing. rings and electrode-supporting members in the
of the wall section and includes a ?at radial ?ange ex
envelope. In prior art devices expansion and contractions
tending a substantial distance outwardly of the ceramic
of the electrode-supporting members have resulted in seal
section. A pair of ceramic wall sections are joined by
failures.
a bead weld between the edges of the outwardly extending
Additionally, in some prior art ccramic-and-metal en
?anges of sealing rings on adjacent opposed ends of the
velope assemblies di?iculties have been encountered in
wall sections. The cathode end of the envelope is closed
incorporating in the structures cooling arrangements which
by a similar weld between the edge of the ?ange of a
will not subtract from the effectiveness and strength of
sealing ring on the outer end of a ceramic wall section
ceramic-to-metal seals in the structure. Also, di?iculties
Heretofore, electric discharge devices have been manu
factured with ceramic-and-metal envelopes completed
by ?rst stacking the various ceramic and metal elements
have been encountered in the appearance of corona at
and a similar ?ange on a metal end member of the en
the seals which have caused undesirable effects, such as
velope. Electrode support members in the envelope in
clude outwardly extending ?anges disposed between but
not directly connected mechanically to the sealing rings.
Spacers corresponding in thickness generally to the thick
damage to the insulation of equipment parts adjacent the
tube.
‘My invention contemplates the provision of an en~
velope construction adapted for being fabricated in in
dividual ceramic-and-metal sub-assemblies or modules
which can be individually tested for leaks and subse
ness of the supporting-member ?ange are welded in place
between the outwardly extending ?anges of the sealing
rings. A plurality of electrode-supporting member ?anges
quently joined using any number of desired modules to 45 can be positioned between the sealing rings, in which case
a spacer or plurality of spacers equal in total thickness
complete an envelope construction of any desired size.
generally to the combined thickness of the support mem
Additionally, my invention contemplates the provision of
ber ?anges is positioned and welded between the outer
sealing arrangements whereby the subsequent assembly
?anges of the sealing rings. The anode end of the en
may be readily disassembled, reworked and rescaled
velope is closed by a cup-like anode member reentrant in
should this be necessary, as well as the provision of means
the uppermost ceramic wall section and includes a ?at
for effecting a satisfactory electrical connection between
?ange sealed to a ?at annulus which, in turn, is sealed at
electrode-supporting members in the envelope and the
the outer edge thereof by a bead weld to the outer rim of
‘sealing rings, while minimizing undesirable transmission
one of the described sealing rings bonded to the upper
of strain to the sealing rings. Further, my invention con
templates the provision of a ?uid-cooled anode arrange
end of the uppermost ceramic section. Bonded to the
ment wherein the cooling means is supported rigidly and
bottom of the anode member is a cooling ?uid conduit in
for minimizing stresses at the adjacent seals. Still fur
cluding upwardly extending end portions. The end por
ther, my invention contemplates provision of means for
tions are bonded in a ‘?at annulus joined at the rim there
avoiding corona formation in those regions of the de
of'to the ?rst-mentioned annulus by the same bead weld
vice where corona is prone to appear.
60 which joins the latter to the sealing ring. Provided about
Accordingly, the primary object of my invention is to
at least one of the sealing rings and covering the U-shaped
provide a new and improved ceramic-and-metal envelope
section thereof and extending into the region between that
construction.
section and ‘the outer wall of the corresponding ceramic
Another object of my invention is to provide a new and
improved ceramic-and-metal envelope construction, the
size of which is not limited by the size of available braz
ing furnaces.
Another object of my invention is to provide new and
improved means for enabling the testing for faulty seals
section is an annulus of a high heat resistant insulative
material.
For a better understanding of my invention, reference
may be had to the accompanying drawing wherein:
FiGURE 1 is a sectionalized partially fragmentary
between ceramic and metal components of an envelope 70 ‘illustration of an electric discharge device constructed in
accordance with the several features of my invention;
construction before completion of the assembly of the
*FIGURE 2 is an enlarged fragmentary sectional view
over-all envelope.
3,082,347
4.
of a seal between ceramic sections according to my in
thickness generally to the thickness of the ?ange 22 of
vention;
the grid support member and has an inner diameter at
least slightly greater than the outer diameter of the grid
.
_
FIGURE 3 is an enlarged fragmentary sectional view
of the envelope end sealing arrangement of my invention;
and
:FIGURE 4 is an enlarged fragmentary sectional view
illustrating a modi?ed form of my sealing arrangement.
Referring to FIGURE 1, the various features of my
support ?ange 22 so as to avoid stress-transmitting en
gagement. The outer edge of .the spacer 23 and the
outer edges of the ?anges 19 are in register and are
joined by a bead weld 24.
The grid cup 3v can be sup
ported and sealed in the envelope between the ceramic
sections 7 and 8 in the same manner as the grid 4.
invention are therein illustrated in an electric discharge
Sealed to the upper end of the ceramic section 8 is
device of the hydrogen thyratron type comprising an 10
another sealing ring 17 brazed to the upper end of the
envelope 1, a cathode and reservoir assembly 2, a first
section 8 in the same manner as the previously described
grid assembly 3, second grid assembly 4, and an anode
assembly 5.
‘
The envelope 1 comprises three generally tubular axially
rings 17 are brazed to the other ends of the ceramic sec
tions 6—8. Extending into the ceramic section 8 is as
aligned ceramic insulator sections 6, 7 and 8. The sec 15 cup-like anode member which also serves as the end c1o-‘
tions 6—8 may be formed of any suitable high-strength _ sure of the envelope. As perhaps better seen in FIG-’
URE 3, the cup-like member 25 includes an outwardly
and highly refractory ceramic material adapted for being
extending ?ange 26 which rests upon the inwardly ex
metalized in order to facilitate the provision of ceramic
tending ?ange 20 of the sealing ring 17 and is bonded
to-metal bonds between the insulator sections and metallic
sealing rings disposed therebetween. For example, the
at its edge in a step 27 formed in a relatively thicker
sections 6 to 8 may be suitably formed of ceramic mate
rials generally known in the art as “alumina,” which ma
areas in the manner disclosed in US. Patent 2,667,427
circular ?at annulus or sealing plate 28. The sealing
plate 28 corresponds in outer diameter to the ?ange 19
of the sealing ring 17 and the outer edges of these ele
ments are in register and hermetically joined by a bead
issued January 26, 1954 to Henry J. Nolte and assigned
weld 29.
terials are adapted for being provided with metalized
to the same assignee as the present invention.
The cathode and reservoir assembly 2 includes a header
'
Provided for assisting in the cooling of the anode is
a cooling ?uid conduit 30.
The conduit 30‘ includes a
?at coiled portion 31 and a pair of upright end portions
32. The coil portion is bonded in a high heat transfer
10 supports in, a suitably insulated manner a plurality
of electrical leads 11 which extends through the header 30 ring manner to a thermally conductive plate 33 which is,
in turn, similarly bonded to the bottom of the cup-like
in a sealed manner and internally of the envelope sup
anode member. Thus, a cooling ?uid circulated through
port and make suitable electrical connections to a cath
the conduit is effective for carrying away heat from the
ode structure 12 and a hydrogen reservoir 13. Electri
anode. Mounted centrally in the plate 33 is an anode
cally connected to the outer ends of the leads 11 ‘are
?exible conductors 14. The header 10‘ is suitably her 35 terminal post 34.
Provided for supporting the upright end portions 32
metically bonded, as by a bead weld, in a tubular seal
of the conduit is a metal annulus 35. The annulus 35
ing ring 15 formed to include a ?at ?ange 16 extending
is provided with suitable apertures through which the
radially outwardly of the envelope wall a substantial dis
ends of the portions 32 of the conduit extend for being
tance. Sealed to the ?ange 16 is a sealing ring generally
10 closing the lower end of the envelope 1. The header
designate-d 17 which can be suitably formed of copper 40 secured in a suitable manner to the annulus. If desired
the ends of the portions 32 can be provided with con
.clad chrome iron. The sealing ring ‘17 is shaped to include
nectors for connecting the conduit in a ?uid circulating
a U-shaped section 18, a ?at ?ange 19 extending out
system. The annulus 35 is bonded at the outer edge
wardly a substantial distance from the U-shaped section
thereof to both the annulus 28 and the sealing ring ?ange
and a relatively short ?at inwardly extending ?ange 20‘.
The edges of the ?anges 16 and 19 are in register and 45 19 by the bead weld 29. Additionally, the central open- '
ing of the annulus provides access to the'terminal post
are hermetically bonded by a bead weld 21.
34, and the rim of the opening is turned down to lend
The lower end of the ceramic section 6 is disposed in
greater rigidity to the annulus.
' '
the sealing ring 17 and the'inner side portion of the U
It will vbe understood from the foregoing that theear
shaped section 18 of the ring is bonded to a suitably
rangement including the annulus bonded to the members
previously metalized lower end of the ceramic insulator
29 and 19 provides for sturdy mounting of the conduit
6, as my means of a silver-copper brazing material. Thus
ends on the upper end of the tube without adversely
a lap seal is provided between the side surface of the
affecting the ceramic-and-metal seal thereof, the annulus
lower end of the ceramic 6 and the sealing ring and a
28 and the sealing ring 17 being e?ective vfor minimizing
highly satisfactory compression seal is thereby provided
between the sealing ring 17 and the lower end of the 55 the transmission of stresses from the coil supporting an
ceramic.
,
-
Extending into the ceramic 7 is a cup-like grid support
ing element including an outwardly extending ?ange 22
positioned between the ?anges 20 of the sealing mem
nulus 35 to the uppermost ceramic-to-metal seal.
‘ Additionally, .I have found that the close relative posi
tioning of the anode cup wall and the upper end portion
of the grid cup 3 has resulted in a tendency for corona
bers on the opposed ends of ceramics 6 and 7. In the 60 to form in the exterior of the insulator section 8 in the
region generally designated 36 and located between the '
illustrated structure a single ?anged cup-like element hav
insulator 8 and the U-shaped portion of the upper seal
ing a perforate bottom comprises both the grid and the
mg ring 17. In order to prevent such formation and
. grid-supporting member. However, if desired, the ele
thus minimize possible damage to apparatus that may be.
ment actually comprising the grid can be supported a
separate tubular flanged support member. The ?ange 22 65 located adjacent the tube I have provided an annulus of
is positioned between the ?anges 20 of a pair of sealing
a high heat-resistant material such, for example, as sili
cone rubber which extends downwardly in the region 36
rings 17 bonded to the opposed ends of the ceramic sec
tions 6 and 7 in the same manner as the previously de
and embeds the U-shaped section of the sealing ring while
scribed ceramic 17 is brazed to the lower end of the
leaving the ?ange 19 exposed for welding during assembly
ceramic 6. This structure is perhaps better seen in FIG
and cutting if it should become necessary to disassemble‘
URE 2 in which it is clear that the ?ange 22, while it
the tube for reworking.
is positioned between and engages the ?anges 20, of the
It will be understood from the foregoing that the de
ring 17, is not bonded thereto. As also seen in FIGURE
scribed scaling arrangements enable sub-assemblies or
2, there is positioned between the ?anges 19‘ of the seal~
modules including, for example, a ceramic section and
ing rings, a circular ?at spacer 23 which corresponds in
a pair of sealing rings 17 to be assembled independently
3,082,347
6
and tested for leaks of the seals therebetween. Addi
tionally, the anode sub-assembly including the described
iweld 43 is alsd connected with a pair of spacers 44 which
cooling means can be separately constructed, as can the
on the cups 40.
sub-assembly including the corona inhibiting structure.
Should a leak be detected in any one of these sub-assem
together total the combined thickness of the ?anges 41
Alternatively, a single spacer can be
employed, provided its thickness generally equals the
combined thicknesses of the ?anges 41. In this embodi
blies, it can either be repaired or discarded. Subse
ment also the inner diameter of the spacers 44 is greater
quently, a number of sub-assemblies can be easily as
than the outer diameter of the ?anges 41 to avoid any
sembled by stacking in the manner shown with the grid
direct contact between these elements which could result
cups set in place between appropriate sub-assemblies and
in strains being transmitted to the seals between the seal~
by joining by means of the bead welds the adjacent ?anges 10 ing rings 17 and the ceramic sections. It will be under
such, for example, as the ?anges 16 and 19 at the lower
stood, however, that if the ?anges 41 should expand
end of the assembly or the ?anges 19 in the intermediate
sufficiently and engage the spacers 44 the latter elements
portions of the assembly or the ?anges 19 and 28 at the
will have some desirable constraining effect as does the
upper end of the assembly. By so uniting the ?anges the
annulus 35 at the upper end of the envelope.
device can be hermetically sealed without inserting the 15
While I have described speci?c embodiments of my
over-all device in a brazing furnace. Additionally, should
invention 1 do not desire my invention to be limited to
a leak be detected in the thus assembled structure any one
the particular forms known and described that I intend
of the bead welds joining the ?anges can be easily cut
by the appended claims to cover all modi?cation within
away and subsequently rewelded after correction of the
the spirit and scope of my invention.
defect or insertion of a non-defective sub-assembly.
20
What I claim as new and desire to secure by Letters
Still further, when the device is at least partially evacu
Patent of the United States is:
ated the axial thrust on the ends of the assembly afforded
,1. An electric discharge device envelope comprisinga'
by external atmospheric pressure serves to press the en
tubular ceramic wall section, a metal sealing ring includ
velope elements together, whereby the ?anges 22 of the
ing an integral generally U-shaped section and a ?at ?ange
grid elements are securely held in place. Thus, these 25 extending radially a substantial distance outwardly of
elements are assured of being held in place in satisfactory
said U-shaped section, said wall section being disposed
electrical contract between the sealing rings without the
in said sealing ring and having the outer side surface
transfer to the seals of any undesired strains resulting
thereof lap-sealed to the inner side portion of said U
from thermal expansion and contraction of the grid cups
shaped section by a metallic bond to provide a hermetic
which could result were the ?anges 22 bonded to any 30 compression seal therebetween, another Wall section of
portion of the sealing rings 17. Additionally, in my ' said envelope bearing on said ?rst-mentioned wall sec
arrangement it is possible to lift these parts out of the
tion and including a ?at radially outwardly extending
assembly easily should it become necessary to separate
metal ?angehaving an edge registering with that of said
the sub-assemblies and rework the parts. The spacers 23
?rst-mentioned ?ange, and a metallic bond joining only
at the grid contact seals serve to avoid any undesirable
the registering edges of said ?anges.
‘
stresses in the sealing ring 17 which might occur where
2. An electric discharge device comprising an envelope
it is necessary to compress the ?anges together to com
containing a reduced atmosphere and including a tubular
pensate for the spacing between the inner ?anges 20
ceramic wall section, a metal sealing ring including an
caused by'the insertion therebetween of the ?anges 22. 1
integral generally _U-shaped section and a ?at ?ange ex
However, it will be understood that in some applications 40 tending radially a substantial ‘distance outwardly from
the ?anges 19_can be su?iciently thin and Wide radially
said U-shaped section, said wall section being disposed
so that they can be easily pressed together for welding
in said sealing ring and having the outer side surface
without enlarging the seals and thus avoiding the need
thereof lap-sealed to the inner side portion of said U
for the mentioned spacers. The use of the spacers 23
shaped
section by a metallic bond, another wall section
also avoids the necessity for forming the ?anges 19‘ and 45
on the end of said ?rst-mentioned wall section
20 of the sealing rings at different axial levels. Thus, _ bearing
and including a radially outwardly extending ?at metal
the sealing rings 17 can the of uniform simple manufac
?ange having an edge registering with that of said ?rst
ture and spacers of di?erent thicknesses can be employed
mentioned ?ange, a metallic bond uniting the registering
where necessary.
of said ?anges, and cup-shaped electrode extend
Additionally, the ?ange 26 of the anode cup is not 50 edges
ing reentrantly in one of said Wall sections and including
bonded to the ?ange 20 of the uppermost sealing ring 17
a ?at radial ?ange positioned between the ?rst and sec
and, thus, any expansion or contraction movement of
ond—mentioned ?anges and not ?xed to any of the afore
the ?ange 26 is not transmitted directly to the ceramic
said elements, whereby the axial atmospheric thrust on
to-metal seals at the upper end of the device. In this ar
both
ends of said envelope is effective for holding said
rangement the heavier ring 28 serves to constrain such
electrode in place and the transmission of strain from
thermal expansion and contraction movements of the
sald electrode to said metallic bonds is minimized.
?ange 26 as does the annulus 35. Additionally, any
3. An electric discharge device according to claim 2,
strain that would ordinarily be transmitted to the sealing
wherein at least one, circular spacer corresponding gen
ring 17 through the plate 28 will be absorbed by the
erally in thickness to the thickness of said electrode
U-shaped section of the sealing ring.
.
?ange
is interposed between the outer edges of said ?rst
Still further, the U-shaped section of the rings 17 pro
and
second-mentioned
?anges, and said metallic bond
vide for the lap ‘seal between the rings and the ceramic
at the outer edges of said ?anges unites the registering
insulators.
edges of said ?rst and second-mentioned ?anges and said
In some structures it is desirable to de?ne within a
spacer.
device a hollow metal assembly such as a cavitygrid. 65
4. An electric discharge device comprising a pair of
As illustrated in FIGURE 4, my invention enables the
axially aligned tubular ceramic wall sections, a pair of
construction of such an assembly employing a pair of
opposed cup-like grid elements 40 including outwardly
extending ?anges 41 in abutting relation and disposed
sealing rings each including an integral U-shaped sec
tion, a ?at ?ange extending radially a substantial distance
outwardly of the U-shaped section and a relatively short
between the ?anges 20 of a pair of sealing members 17 70
?ange extending inwardly of said U-shaped section, said
of the type described above and sealed to the ends of a
pair
of sealing rings having the U-shaped sections thereof
pair of ceramic sections 42 which can be identical to the
oppositely disposed, having the edges of said outwardly
above-described ceramic sections. In this arrangement
extending ?anges registering and united by a metallic
the ?anges 19 of the sealing rings 17 are joined at their
bond
and having the relatively short ?anges thereof in
registering outer edges by a bead weld 43. The head 75
mutual bearing relation, and said wall sections each hav
3,082,347
7
ing an end disposed in one of said sealing rings and hav
ing the outer surface thereof lap-sealed to the inner side
portion of the U-shaped section thereof to provide a com
3
crete rigid annular metal element having its outer edge
bonded to the outer edge of said sealing ring and its in
nor edge bonded to said rim portion of said electrode,
cooling means positioned in said electrode and includ
pression seal therebetween and the end surface bearing
U! ing coolant conduit portions extending outwardly of the
on said inwardly extending ?ange.
said cup-like electrode, and a plate-like member posi~
5. An electric discharge device according to claim 4-,
wherein a supporting member extends in one said ce
tioned over the open end of said cup-like member and
positioned between said inwardly extending ?anges of
having the rim thereof joined to said rigid annular metal
element, and said plate-like member having said conduit
thickness generally to said supporting member ?ange and
‘[0.
ramic sections and includes an outwardly extending ?ange
said seal-ing rings, and a circular spacer corresponding in 10 portions extending therethrough and rigidly joined there
9. An electric discharge device comprising a tubular
ceramic wall section, a sealing ring including an integral
U-shaped section, a ?at ?ange extending radially a sub
said outwardly extending ?anges of said‘ sealing rings.
6. An'electric discharge device according to ‘claim 4, 15 stantial distance outwardly of said U-shaped section and
a relatively short inwardly extending ?ange, said wall
wherein a pair of oppositely disposed cup-shaped elec
section having an end disposed in said ring and having
trode members each extends reentrantly in one of said
‘the outer side surface thereof lap-sealed to the inner side
ceramic sections and include outwardly extending abut
portion of said U-shaped section to provide a compres
ting ?anges which are positioned between said inwardly
extending ?anges of said sealing rings but are directly 20 sion seal therebetween, a cup-like member extending in
said wall section and including an outwardly extending
unconnected thereto, and at least one circular spacer cor
?ange resting on said inwardly extending ?ange on said
responding in thickness generally to the thickness of said
sealing ring, a discrete ?at circular metal member of rel
supporting member ?anges and having an inner diameter
atively more rigid ‘construction than said sealing ring
greater than the outer diameter of said last-mentioned
having the inner edge bonded to the outer edge of said
?ange ‘is sealed between said outwardly extending ?anges
?ange on said cup-like member and the outer edge regis
of said sealing rings.
tering with and bonded to the outwardly extending ?ange
7. An electric discharge device comprising a tubular
of said sealing ring, cooling means positioned in said
ceramic wall section, a sealing ring including an integral
cup-like member and including coolant conduit portions
vU-shaped section, a ?at ?ange extending radially a sub
extending outwardly thereof, and a discrete second ?at
stantial distance outwardly of said U-shaped section and
circular metal member having the rim thereof bonded
a relatively short inwardly extending ?ange, said wall
to' said ?rst~mentioned circular member, said sealing ring
section having an end disposed in said ring and having
said said second-mentioned ?at circular member, said
the outer surface thereof lap-sealed to the inner side por
second ?at circular member having end portions of said
tion of said U-shaped section to provide a compression
seal therebetween, a cup-shaped electrode supporting 35 conduit extending therethrough and being rigidly bonded
thereto.
member extending reentrantly in said wall section and
including an outwardly extending ?ange resting on said
References Cited in the ?le of this patent
inwardly extending ?ange of said sealing ring, and a
discrete ?at circular metal member having the inner edge 40
UNITED STATES PATENTS
bonded to the outer edge of said ?ange on said support
1,734,208
Golladay __________ __~___ Nov. 5, 1929
member and the outer edge registering ‘with and bonded
2,440,245
Chevigny ____________ __ Apr. 27, 1948
having an in?'er diameter greater than the outer diam
eter of said last-mentioned ?ange and is sealed between
to the outwardly extending ?ange of said sealing ring,
said discrete ?at circular member being of substantially
more rigid construction than said ?anges, whereby it is 45
elfective for minimizing strain transmission to said com,
pression seal.
8. An electric discharge device comprising a tubular
ceramic wall section, a seal ring joined to one end of
said wall section, a ‘cup-like electrode reentrant in said
one end of said wall section and having a rim portion
hermetically joined to said sealing ring through a dis
2,569,872
Skehan et val ____________ __ Oct. 2, 1951
2,677,781
Drieschman ___________ -_ May 4, 1954
2,782,952
Dalton ____ ._‘_ ________ __ Febt26, 1957 r
2,789,154
Peterson ____________ __ Apr. 16, 1957
2,890,377
Fyler ________ _..‘. ______ __ June 9, 1959
2,939,988
Culbertson et al ________ __ June 7, 1960
121,879
Russia ___; ___________ __ Aug. 4, 1958
FOREIGN PATENTS
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,
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