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Патент USA US2107518

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Feb. 8, 1938.
2,107,518
c. s. BULL ET AL
ELECTRON DISCHARGE DEVICE
Original Filed Dec. 24, 1934
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Patented Feb. 8, 1938
2,107,518
UNITED ‘STATES ; PATENT OFFICE
'
2,107,518
ELECTRON DISCHARGE DEVICE
Cabot Seaton Bull, Hillingdon, and Sidney Rodin,
En?eld, England, assignors to Electric and Mn
sica-l Industries Limited, MiddleseX, Ensland,v a
company of Great Britain
.
-
Application December 24, 1934, Serial No. 759,008.
Renewed September 18 , 1937. .In Great Britain
. January ,8, 1934
16 Claims.
The present invention relates'to electron dis
charge devices and more particularly to therm
ionic valves of the kind commonly known as
tetrodes having an anode, a cathode and, between
‘ the anode and cathode, two grid electrodes.
It is known that valves of this kind ‘tend to
have their performance adversely affected by
secondary electron emission from the anode to
the screen grid electrode (that is the grid elec
10 trode nearer the anode) when, in operation, the
15
anode potential falls below that of the screen
grid. In order to reduce or prevent such second~
ary emission it has been proposed to make use of
an additional grid between the screen grid and
anode.
.
,
Another way in‘ which secondary emission can
be reduced or prevented is to cause a space charge
to be. set up in the space between the anode and
screen grid and it is an object of the present in
(Cl. 250—27.5) _
with the anode. If the shields are of insulating
material, whether coated with conducting mate
rial or not, they become charged by the electrons
and assume a potential approaching that of the
cathode. I1‘ the shields are of conducting mate
rial or have a conductive coating they may be
connected with a point of low potential, for ex
ample the cathode, or they may be left uncon
nected. In any case the shields assume a low
potential relative to the anode and serve to direct 10
the electron stream on to an unshielded part of
the anode surface.
According to a further featureof the present
invention, in a discharge device comprising a
cathode surrounded, in the order named, by a 15
control grid, a screening grid and an anode, in
which the anode forms part of the envelope of
the‘ device, one or more shielding members are
disposed between the anode and the screening
20 vention to provide a tetrode of this kind in which - grid, these shielding members extending over a
~ the anode may act‘as part of the envelope of the substantial fraction of the anode surface and 20
discharge device.
Discharge tubes having an
anode acting as part of the envelope and methods
for making such tubes are for example described
in United States patent speci?cations numbered
1,914,634, 1,942,824 and‘1,965,408 and in British
' patent speci?cations numbered 369,052, 370,174,
371,992 and 389,170, and many of the features and
methods described in these speci?cations can with
80 advantage be applied to valves according to the
present invention.
According to the present invention, in an elec
serving substantially to prevent electrons‘ from
reaching the anode over this part of its surface.
The invention will now be described by way of
example with reference to the accompanying dia 25
grammatic drawing, wherein the Figures 1, 2, and
3 represent sections of electron discharge devices
. according to this invention.
-
Like parts in the various figures are ‘indicated
by like references.
30
In all the figures of the drawing a metal cylin
der l is arranged to form part oi’ the envelope
tron discharge device comprising, in the, order of a discharge device and to act as anode. Within,
v:named, a cathode, a- control grid, a screen grid" the anode I and coaxial therewith is arranged a
v‘and an anode, there is provided in the space be
rod shaped cathode 2. The cathode is sur
tween the screen grid and anode one or more rounded by a control grid 3 which is supported by 35
shielding members extending over a consider ‘ two rods 4, 5 lying ‘in a diametralplane. The grid
able portion of ‘the anode and adapted to shield 3 may be formed of ,wire wound helically upon
from the cathode a substantial fraction of the the rods 4, 5 and is diamond shaped, the four
40 total surface of the anode which is directed to corners being rounded and the longer diagonal 40
' wards the cathode. For example, when the anode lying in the plane of the supporting rods. Around
surrounds the cathode, two shielding members ’ the control grid 3 is a screening grid 6 which may
may be provided and each may extend about one
quarter of the way around the anode surface and
together the members may shield from 'the
cathode about one half of the ‘total anode sur
face directed towards the cathode. The shielding
members may be of insulating material and may
be arranged in contact withthe anode. Alter
50 natively‘ the members may be spacedirom the
anode and in that case they may be of conduct
ing material. If the shielding members are of
insulating'material they may be wholly or partly
coated with conducting material, this conducting
55 coating being in any case out of electrical contact
be of the same shape as the control grid and is
also mounted upon two supporting rods 1, 8 ar
ranged in the same plane as the rods 4, 5. p
45
Between each of the outer supporting rods 1, 8
and the anode are arranged one or more shield
ing members.
.
'
In the example shown in Fig. 1 these shielding
members are in the form of arcuate strips 9, III 50
of insulating material such as glass arranged par
allel to the anode axis and preferably extending
over the whole“ axial length of the active surface
_ ‘ of the anode.
_ In Fig. 2 the shielding members take the form
2,107,518
of pieces of glasstube ll, I2 01’: diameter ap- ;
2. An electron discharge device having ‘an
evacuated envelope and’ arranged within said en-"
- the anode I. The tubes Ii, I2 are mounted with " velope, in the order named, a_ cathode capable of
their‘ axes in the plane of the supporting rods 4, electron emission, a control grid, a screen grid,
proaching the distance between the rods ‘I, 8 and
5
5,1,8.
_
an anode, and shielding means impermeable to '
.
In addition to the'shielding members shown in .electrons'and of insulating material and disposed
Fig. 1, insulating shielding members l3, M in. to shield from said cathode substantially one
contact with the anode may be inserted as shown
in Fig. 3.
T10
.
“
I
.
The shielding members are of such size as to
shield a considerable fraction, preferably about
one-half, of» the anode surface from the cathode
emission.
_
,
.
half of the ‘total surface of'sa'id anode which is
directed towards said cathode.
3..An electron discharge device having an 10‘
evacuated envelope and arranged within said
envelope, in the order named, a cathode capable
of electron emission, a control grid, a, screen grid,
If the spacing of the electrodes is suitably
15 chosen for the conditions under which ‘the dis
charge tube is to'work, it will be‘found that a
space charge is setup in that part of the space
between the cathode and the anode which is not
shielded by the glass tubes or rods, the tubes or
‘a 20
rods becoming charged by impinging electrons
and serving to de?ect electrons intothis part of
the space. The space charge serves‘ to prevent
secondary'electron emission from the anode to
the screening grid or at least to reduce such
25 secondary emission.’
'
shielding means and an anode, said anode having
a surface directed towards said cathode and said
shielding means comprising at least one member
of insulating material coated with conducting
material on the surface thereof directed toward
said cathode and extending over a substantial
fraction of said anode surface.
’
' .
4. An electron discharge device having: an
evacuated envelope and arranged within said en
velope, in the order named, a cathode capable of
electron emission, a control grid, 2. screen grid,
shielding ‘means and an anode, said, shielding
The shielding membersmay'be coated with' means being in the form of a coating of insulat
conducting material which may be connected to a
- point of relatively low potential, for example to
the cathode. Preferably, however, if the con
ductive coating is applied, it is not connected
electrically but is allowed to assume a'working'
potential by electron bombardment. Where two
ing material upon the surface of said ‘anode
directed towards said cathode and extending over
a substantial fraction of said surface.‘
"
'
5. An electron discharge device having an 30
evacuated envelope‘and arranged‘ within said en
velope, in the order named, a cathode capable of
shielding members are provided on each side, as ; electron emission, a control grid, a screen grid,
shown in Fig. 3, conductive coatings may be api
,plied to’ the outersurfaces of the inner shields
9, l0 and the inner surfaces of the outer shields
l3, IA. ’The coating may be of silver and may
having a surface directed towards said cathode
and‘an opposite surface in c0ntact_with a surface
be applied by providing a number of silver pellets
of said anode and extending over a substantial
within the tube, for example upon the screen grid.
fraction of said anode surface.
_When the valve is being “gettered” the silver
melts and condenses upon the shields or at least
upon parts thereof. When a ‘shield in contact
with the anode is to be coated in this way,‘it is
preferably undercut at’ its edges‘ as ’shown at IS
45 in Fig. 3 in such a way as to make the surface in
contact with the anode of smaller area than the
opposite surface. In this way it is ensured that
the coated surface remains insulate-d from the
anode.
'
h
'
In some cases shields of -~.conducting material,
arranged out of contact with the anode, may be
used.
‘
r The above description is given by way of ex
ample only and many modi?cations of the in
55 vention will be apparent to those versed in the
art.
-
_
For example, the'anode need not always form '
La part of the envelope but may be a suitablev
shaped electrode arranged within an envelope
60 for example of glass. Further, cathodes of other
than rod shape may be employed and the grids
may be of circular, oval or other suitable shape
in plan view. 0ther suitable methods of sup
porting the grids may be employed.
We claim:
_
shielding means and an anode, said shielding
means being in the form of insulating material 35
'
1. An electron discharge device _having an
evacuated envelope and arranged within said en
velope, in the order named, a cathode capable of
electron emission, a control grid, a screen grid,
70 an anode forming part of said envelope and hav
ing a surface directed towards said cathode and
shielding means having a closed surface of sub
‘ stantial area impermeable to electrons and being
-
6. An electron discharge device having an 40
evacuated envelope and arranged within said
envelope, in'the order named, a cathode capable
of electrong emission, a control grid, a screen
grid, shielding means and an anode, said shield
ing means being inthe form of insulating mate 45
rial having a surface directed towards said
cathode coated with conducting material and an
opposite surface in contact “with a substantial
fraction of the. surface of said anode which is
directed towards said cathode, the edge surfaces
of said insulating material being undercut to
make the area of the second named surface
v"smaller than that of the ?rst named surface.
'7. An electron discharge device having an
evacuated envelope and arranged within said en
velope, in the order named, a cathode capable of
electron emission, a control grid, 2. screen grid, a
?rst shield member, a second shield member and
an anode, said shield-members extending over a
substantial fraction of the surface of said anode 60
directed towards, ‘said cathode, and said shield
members having surfaces facing one another,
these surfaces ‘being coated with conducting
material.
'
'
8. An electron discharge device having an
evacuated envelope and arranged within said en
velope, in the order named, a cathode‘ capable
of electron emission, a control grid, a screen grid,
shielding, means and an anode, said shielding
means being substantially impermeable by elec 70
trons and extending over substantially-one half
of the surface of said anode directed towards said
' cathode.
V
9. An electron discharge device -comprising1.;a<
disposed to shield from said cathode substantially
_ cathode capable of electron emissionviandi-ianqg
7'5 one-half'of said anode surface.
9,107,518
evacuated envelope including an anode surface.
a control grid and a screen grid arranged in the
order named between said cathode and said anode
surface, a rod-like member for supporting said
screen grid and shielding means impermeable to
electrons disposed between said rod-like member
and said anode, said shielding means having a
closed.‘ surface of substantially the same length
as the axial length of the active surface of said
10 anode and of a width to shield substantially
one-half of said active surface.
_ .10. An electron discharge device comprising a
cathode, a control grid, and an anode surround
ing and coaxial with said cathode. a screen grid
15 coaxial with and interposed between said control
grid and said anode and having a supporting rod,
and a ‘shield of insulation and impermeable to
electrons disposed between said supporting rod
and said anode.
20
11. An electron discharge device according to
claim 10 wherein the surface of said shield fac
ing said cathode is coated with conducting mate
rial.
12. An electron discharge device according to
25 claim 10 wherein said shield is in the form ‘of a
coating of insulation on the surface of said anode
facing said cathode.
13. An electron discharge device according to
claim 10 wherein said shield of insulation has an
30 inner surface facing said cathode and an‘ outer
surface in contact with said anode, the edges
of said insulation being undercut to make the
area of its outer surface less than that of its
inner surface.
..
y
14. An electron discharge device according to
claim 10 wherein said shield of insulation is cy
lindrical in form.
15. An electron discharge device comprising a
cathode, an anode surrounding said cathode, a
control grid‘ and av screen grid coaxial with and
interposed between said cathode and said anode,
and a pair of shields mounted between said screen 10
grid and said anode on opposite sides of said
‘screen grid and extending over the axial length of
the active surface of said anode and each of a
width toshield substantially one-fourth of the ac- '
tive surface of said anode from said cathode emis
sion.
15
'
16. An electron discharge device comprising a '
cathode, a grid surrounding said cathode. a sec
ond grid surrounding and coaxial with said
cathode and having a pair of diametrically oppo 20
site grid support rods, an anode surrounding said
second grid, and-apair of arcuate shield strips '
mounted outside of and on opposite sides of said
second grid in alignment with said support rods,
said strips being mounted with their concavities 25
facing each other andeach of said strips being
of substantially the same length as the axial
length of the active surface of said anode and of a
width to shield substantially one-fourth of said
active surface from said cathode.
I
CABOT BEATON BULL.
SIDNEY RODDA.
30
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