U.S. patent number 3,870,393 [Application Number 05/441,053] was granted by the patent office on 1975-03-11 for corona-free top cap terminal assembly for electron discharge devices.
This patent grant is currently assigned to General Electric Company. Invention is credited to Robert L. Hill, Othmar E. Ringeman.
United States Patent |
3,870,393 |
Hill , et al. |
March 11, 1975 |
Corona-free top cap terminal assembly for electron discharge
devices
Abstract
An electron discharge tube having a corona-free top cap terminal
assembly comprising a metallic top cap conductively bonded to the
outer surface of the tube envelope.
Inventors: |
Hill; Robert L. (Owensboro,
KY), Ringeman; Othmar E. (St. Meinrod, IN) |
Assignee: |
General Electric Company
(Owensboro, KY)
|
Family
ID: |
23751315 |
Appl.
No.: |
05/441,053 |
Filed: |
February 11, 1974 |
Current U.S.
Class: |
439/611; 29/874;
174/50.52; 313/318.08 |
Current CPC
Class: |
H01J
5/26 (20130101); H01J 2893/0041 (20130101); Y10T
29/49204 (20150115) |
Current International
Class: |
H01J
5/26 (20060101); H01J 5/00 (20060101); H01j
005/06 () |
Field of
Search: |
;174/50.52 ;29/63G,25.11
;339/275R,143C,144R,144T ;313/318 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truhue; J. V.
Assistant Examiner: Tone; David A.
Attorney, Agent or Firm: Dearing; D. A. Neuhauser; F. L.
Claims
What I claim is new and desire to secure by Letters Patent of the
United States is:
1. An electron discharge tube comprising:
a. an evacuated envelope having a top wall portion with an external
protuberance thereon;
b. at least one electrode sealed within said envelope;
c. a lead wire extending from said electrode, said wire passing
through and sealed in said protuberance;
d. a cup-shaped top cap terminal disposed over said protuberance
with the rim of said top cap disposed adjacent an outer surface of
said top wall portion, and said top cap electrically connected to
said lead; and
e. an electrically conductive cement disposed between said top cap,
said protuberance, and said surface providing an electrically
conductive path between said top cap rim and said surface and
bonding said top cap to said protuberance and said top wall
portion.
2. The tube of claim 1 wherein said cement is a mixture of epoxy
and conductive particles.
3. A method for attaching a cup-shaped top cap terminal on an
electron discharge tube, said tube comprising a plurality of
electrodes in an envelope, a lead wire extending from one of said
electrodes through said envelope and said top cap, said method
comprising:
a. providing an electrically conductive cement; and
b. disposing said cement and said cap over a portion of the
exterior surface of the envelope through which the lead extends so
as to permit the formation of an electrically conductive bond
between said cap and said portion.
4. The method of claim 3 wherein said cement is provided in a
preformed, non-tacky state, said method further comprising heating
said portion, said cement and said cap to form said electrically
conductive path thereamong.
5. The method of claim 4 wherein said portion has a protuberance
through which said lead extends; said cement is provided in a
preformed shape of an annular ring; and said cement and said cap
are disposed around said protuberance prior to heating.
Description
BACKGROUND OF THE INVENTION
This invention relates to methods and apparatus for manufacturing
electrical devices and, more particularly, to a method and
apparatus for making a top cap terminal assembly for electron
discharge tubes.
Conventionally, the top cap terminal for high voltage electron
discharge tube comprises a cup-shaped metallic member cemented to
the top of the glass envelope, for enclosing the tube electrodes,
with the rim of the cup-shaped member disposed adjacent the
envelope. Viscous fluid, paste, and preformed cements are known
types of bonding agents for fixing the top cap terminal to the
envelope. Electrical connection between the top cap and the anode
is provided via a lead wire extending through the envelope which is
welded or soldered to an aperture in a top wall of the top cap. The
envelopes for such tube are typically provided with a conductive
getter flash or deposit on the inside surface of the envelope to
enhance the vacuum therein. The flash is usually disposed on the
inside surface of the envelope opposite the top cap.
Heretofore, such tubes have suffered from the problem that
electrical noise is generated during the use of such devices in
television receivers. It was discovered that the primary source of
such electrical noise was a corona or electrical discharge between
the rim of the top cap and the envelope at points where the rim was
spaced from the surface of the envelope. A secondary source of
electrical discharge has been found to be between the anode lead
wire and the getter deposit on the inner surface of the envelope
opposite the top cap. This deposit is usually in electrical contact
with the lead wire during the early life of the tube, but the
contact can become broken because the deposit is thin and will
deteriorate over the life of the tube.
In addition to the electrical noise created by the corona, it has
been found that the envelope, which is conventionally made of
glass, will be severely damaged during the life and operation of
such devices and can result in the tube eventually becoming
defective.
The primary source of this problem appears to have been recognized
and discussed in U.S. Pat. No. 3,727,088 of Allgaier issued on Apr.
10, 1973. The Allgaier patent suggests that this source of the
problem can be solved by maintaining the getter assembly at anode
potential.
Other solutions which have been suggested are the provision of a
conductive paint or coating on the external surface of the envelope
adjacent the rim of the top cap, thereby to provide a conductive
path between the top cap rim and the envelope. This was found to
eliminate the corona problem but was found to be unsatisfactory
because of the extra cost and labor required to put the conductive
paint on the surface. Furthermore, the paint was found to require
careful application to prevent the paint from being applied to the
surfaces of the top cap and envelope to be bonded. If the paint is
applied to these surfaces, a defective or weak bond can be
produced.
Accordingly, it is an object of this invention to provide an
electron discharge tube with an improved top cap terminal assembly,
thereby avoiding the problems associated with the prior art.
It is another object of this invention to provide an electron
discharge tube having a top cap terminal assembly conductively
bonded to the tube envelope.
It is still another object of this invention to provide a top cap
terminal which can be conductively bonded to the tube envelope in a
simple and inexpensive manner.
Other objects of the invention will be apparent from the following
description and accompanying claims.
SUMMARY OF THE INVENTION
In accordance with this invention, an electron discharge tube is
provided comprising a tube envelope with a protuberance thereon, a
cup-shaped top cap terminal disposed about said protuberance with
the rim of the top cap disposed adjacent the outer surface of said
envelope, said top cap being bonded to said envelope by an
electrically conductive cement, thereby to provide an electrically
conductive path between said top cap and said envelope.
In accordance with another aspect of the invention, a method for
attaching a cup-shaped top cap terminal to an electron discharge
tube comprises providing an electrically conductive cement,
disposing said cement and said cap over an exterior surface of the
tube envelope, so that an electrically conductive bond can be
formed between said surface and said cap.
The invention will be better understood after consideration of the
following description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a view of a fragmentary axial section of an electron
discharge tube with a top cap terminal constructed in accordance
with this invention.
FIGS. 2A and 2B illustrate the steps of attaching a top cap
terminal to a tube envelope in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, and more particularly to FIG. 1, there
is shown an electrical element 11, which may be an anode or other
electrode, of a sealed discharge device tube type having a top cap
13 and a lead wire or top cap wire 15 projecting from an opening 17
in the top surface of the top cap 13. The tube type may otherwise
be of any conventional construction, such as that shown and
described in U.S. Pat. No. 2,857,544 of J. F. Stephens, patented
Oct. 21, 1958, and assigned to the assignee of this application.
The invention, it will be understood, is equally applicable to any
other tube type wherein a top cap terminal or electrode connection
is required or desired.
The top cap wire 15 fits loosely within the opening 17 of the top
cap 13 during assembly and fabrication of the tube; and when the
fabrication of the tube is completed, the top cap wire 15 should be
firmly, tightly, and conductively secured to the top cap 13. The
cap 13 is a metallic, cup-shaped member of any suitable material,
such as brass, and is secured to the envelope 21 of the tube by an
electrically conductive cement 19. The cement 19, which, in
accordance with this invention, includes a graphite or other
conductive particle filler for good electrical conductivity, is
preferably any general type of epoxy cement which can be preformed
in a partially cured, non-tacky state. Such conductive epoxy
cements are well known and are marketed by Amicon Corporation under
the trademark "Uniset" as product No. SE-902-31.
In FIG. 2A and in accordance with the illustrated embodiment, the
cement 19 is preformed in the shape of an annular ring 25 which can
be slid over a protuberance 24 on the outer surface of envelope 21.
After disposing the preformed epoxy cement 25 in place, the top cap
13 can be threaded over the wire 15 with the rim portion 27 thereof
ultimately disposed adjacent a portion of the outer surface of
envelope 21 surrounding the protuberance 24. The top cap 13 (FIG.
2B) then can be heated by any conventional means 29, such as a gas
burner, to soften the annular ring 25 into a viscous, tacky state
so that, upon curing or hardening, an electrically conductive bond
is formed between the top cap rim 27 and the outer portion of
envelope 21. It can be seen that the outer portion of envelope 21
forms acute angle with the rim 27 so that the cement 19 can flow in
its viscous, tacky state into the tapered space formed therebetween
so as to insure that good electrical contact between the rim 27 and
the outer portion is formed. Accordingly, it can be seen that this
construction will avoid the corona problems noted in some prior art
constructions in a simple and inexpensive manner.
It will be understood by those skilled in the art that the cement
need not be applied in a preformed, non-tacky state and further
that conductive cements other than epoxy-based cements can be used
within the scope of this invention.
After the top cap 13 has been conductively bonded to the envelope
21, the portion of the wire 15 which extends beyond a projection 25
in the upper portion of the top cap 13 is broken or cut off. The
remaining portion of lead 13 extending into the projection 25 is
then welded in accordance with the method set forth in U.S. Pat.
No. 3,192,610 of Keating, issued on July 6, 1965, and assigned to
the assignee of this application, the disclosure of which is
incorporated herein by reference.
Although a particular embodiment of the subject invention has been
described, many modifications may be made, and it is understood
that the appended claims are intended to cover all such
modifications that fall within the true spirit and scope of the
invention.
* * * * *