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Патент USA US2130280

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Sept. 13, 1938.
‘
M. KNOLL
2,130,280
‘ ELECTRON DISCHARGE ‘TUBE
Original Filed April 6, 1934
F119 '1
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“V
INVENTOR
’
BY 7
‘ATTORNEY
2,130,280
Patented Sept. 13, 1938
"UNITED STATES PATENT OFFICE
2,130,280
ELECTRON DISCHARGE TUBE
'Max Knoll, Berlin, Germany, assignor to ‘Tele
funken Gesellschaft fur Drahtlose Telegraphic
.m. b. 11., Berlin, Germany, a corporation of
Germany
Application April 6, 1934, Serial‘ No.' 719,287. Re_
newed July'3, 1937. In Germany April 12,
1933
12 Claims.
‘The. present invention is concerned with dis
charge tubes comprising a cathode, an anode
and one or more interposed grid electrodes, and
~more particularlyawith the construction and dis
"5 mposition ‘of said electrodes in such tubes. The
stream or. current of electrons in discharge tubes
has heretofore been conceived of as being a
stream of a continuous medium (the so-called
“electron gas" or cloud) proceeding from the
cathode or ?lament through the control electrode
to the anode or. plate. However, more recent in
vestigations have demonstrated that a current of
electrons which propagates throimh a broken or
‘apertured electrode such as a grid, is resolved,
"15 ‘under certain circumstances, into discrete con
.stituent or individual pencils ‘or brushes of rays
sharply separated from one another which, in
the presence of sufficiently high speeds and sum
:ciently low current‘densities, exhibit a behavior
satisfying the laws of geometrical electron optics.
‘If an electron having a velocity of Uh enters
betweentwo equipotential surfaces of potential
Uo of the non-homogeneous ?eld at the opening
ofv an apertured or non-continuous electrode, it
25",wil1'be refracted or de?ected, according" to the
sign of the electrode, in the direction of, or away
from, the ‘perpendicular. For the space into
which‘ the electron will get after having passed
through the two equipotential surfaces, there
lBf) will then hold the following index of refraction:
,
On the basis of this law of refraction of elec
‘35 tron-optics, it-is possible to trace, both graphi
cally?and bywcalculation,.the different electron
paths or trajectories on passing through the
equipotentialsurfaces in the openings of aper
tured .-or non-continuous electrodes, in analogy
.withthe behavior of a luminous ray inside a me
exhibiting non-homogeneous refractive
ness.
-
_
~--What- is important and essential in connection
with-the invention hereinafter to be described is
45 a proper appreciation of this fact that the laws
of' electron-optics hold good not only, as is well
known, ‘for highv electron velocities and com
paratively- small currents, but also for relatively
lowvoltages‘and. relatively large currents such
50 as occur . in ordinary ampli?ers, in spite
electrostatic repulsion
of
the
electrons
of
be
tween one another. ‘If the electrode systems
there used are investigated on the basis of
the electron-optical viewpoint rather‘than the
65 hydrodynamic one, as has ‘heretofore been done,
(Cl. 250—27.5)
it will be discovered that the electrons, at the
openings of the various apertured electrodes,
have to deal with or are subject to approximately
cylindrical or calotte-shaped (hemispherical)
equipotential surfaces which come to act upon
them in the way of small lens systems, and the
result is that, posteriorly of each opening of an
apertured electrode, there arises a tiny easily de
?nable pencil or brush of rays, the cross-section
and shape of which is a function of the form and 10
the size of the said opening.
The object of the present invention, by adopt
ing suitable dimensions for the openings of the
apertured electrodes, by the disposition of the
electrodes themselves, by the development of their 15
surface, and by the mutual or relative positions
of the openings of the various electrodes, is to
act upon or influence the characteristic of the
discharge tube in certain or prearranged ways.
By the formation of “electric lenses” as herein 20
before mentioned, inside the openings of aper
tured electrodes-foci will be set up posteriorly
thereof in which the electrons will be focused.
It- is possible to cause the foci to register with
the openings of the next apertured electrode or 25
electrodes so that the passage of electrons there
to (or absorption of electrons by the same) will
be avoided.
This means a great relief for these
electrodes, and this is especially advantageous
whenever auxiliary electrodes maintained at a 30
high positive potential are involved, as is true,
e. g., of screen-grids and space-charge grids.
Moreover, owing to the fact that the electrons
may be'exactly concentrated or focused in the
openings of a control electrode, it is feasible to
secure increased controlling power or accuracy
and greater slope (mutual conductance) of the
tube. By intentional shifting of the foci away
from the center of the opening of the following
apertured electrode it is further feasible to flatten 40
the characteristic, indeed, to impart to the latter
any kind of shape or trend, for instance, to ob
tain also aform following an exponential or
logarithmic law.
If, furthermore, the cathode
surface is given a shape which agrees or con
45
forms with that of the equipotential surfaces
occasioned by an apertured electrode, this affords
a chance, especially in the presence of small
inter-grid distances, to make the load of the
cathode more uniform, to derive or extract from 50
the latter a higher emission, at the same control
voltage, and thus to secure a further increase ‘in
the slope of the tube.
For a better understanding of the basic idea
underlying this invention, the same will be ex
2
2,130,280
plained by reference to the accompanying draw
ing.
In Fig. lis shown a schematic longitudinal sec
tion through the electrode system of a tetrode
tube which comprises a cathode K, a space
charge grid Gs, a control grid Go, and an anode
A. Both grid electrodes, for instance, shall be
assumed to be of the mesh or gauze metal type.
Inasmuch as all parts of the same electrode are
10 at one and the same potential, there arises a
?eld distribution such as indicated in the graphs,
the fine solid lines indicating the form of the
equipotential surfaces.
It can be readily seen
that the potential surfaces between two grid wires
resemble the shape of a biconcave lens, and the
vicinity of an individual grid wire the form of
a biconvex lens.
Whether these equipotential
surfaces exercise one action or the other upon
the electrodes, in other words, whether they focus
or disperse, will depend upon the sign of the
potential gradient in the potential surface in
question, seeing that the electrons in the one
instance are attracted, and are repelled in the
other. In view of the positive potential of the
space-charge grid, the electrons emanating from
the cathode are concentrated in pencils of rays
B which are located exactly posteriorly of the
wires of the space-charge grid. According to
pre-supposition, the control grid is at a negative
potential, and it is for this reason that in this
case, the interstitial spaces between its wires act
like another focussing lens, and focus the elec
trons upon the wire strips of the anode A. It
can be readily understood that the constituent
ray pencils will penetrate through the control
grid without an incidental impediment of their
trajectories if the openings of each grid are ex
actly alike. rI'his stipulation is ful?llable in vari
ous ways, for instance, by that holes of like shape
40
Q In
This circumstance would seem important es
precise mounting and assembling in conformity
with the demand hereinbefore indicated, that is,
correct registering of grid openings, are still
more easily ful?lled.
The use of an additional auxiliary grid in a 30
space-charge grid type of tube is illustrated in
Fig. 3. The electrode system comprises the cath
ode K, the auxiliary Ga, the space-charge grid Gs,
the control grid Go, and the anode A. What
are punched in a lamination or sheet, said holes
being equally spaced apart. The openings could
at the same or at a negative voltage in reference
have also the form of slits running parallel to
the cathode. Also the so-called mesh grids made
of wire gauze satisfy the said condition, at least
approximately so, through in that case it is ad
to the cathode, whereas the space-charge grid,
the ray pencil. t is for this reason that‘ grids
attached to stays constructed according to con
ventional methods would appear unsatisfactory,
While spiral grids, fundamentally speaking, are
55 admissible, for they may be conceived as helically
wound cylinder lenses, it must be borne in mind
that this uniform condition should not be dis
turbed by stays or similar supporting means.
From the distribution of the electrons as illus
trated, it can be seen that when making the anode
or plate from a wire gauze or netting of de?nite
dimensions, favorable thermal radiation is feasi
ble, on the one hand, while, on the other hand,
provided that the pencil of rays impinge exactly
65 upon the anode surface, no electrons will be able
to reach the space in the rear of the anode where
they are liable to give rise to all kinds of trouble.
Fig. 2 shows a cross-section of a tetrode tube
comprising a cathode K, a control grid Go and an
anode A. In addition an auxiliary electrode Go.
is mounted between the control grid and the
cathode which, for the reasons hereinafter to
be discussed in more detail, is so designed and
75 arranged that the openings thereof come to reg
10
pecially when the tube is operated inside the
range of positive grid voltages, inasmuch as then
no grid current will be able to arise, and since
the control potential source is relieved of load.
As a natural result, as will be noted, such distor
tions as will arise normally when working with
in the positive grid potential region, will here be
avoided.
This construction is of utmost importance par
ticularly also in connection with transmitter
valves seeing that in the case of these, on the
one hand, owing to higher‘ operating voltages,
far larger grid currents will arise, while, on the
other hand, due to the large dimensions of the
electrode system, the chances for insuring 25
must be borne in mind is that conditions should
be such that the openings of the space-charge
grid and the auxiliary grid will exactly come to
register, wheras the wires of the control grid
will coincide correctly with the middle of the said
opening. The auxiliary grid again is maintained
visable to roll the gauze down or ?atten it in
order that it may present throughout the same
thickness or gauge; for the requirement of having
uniform thickness in apertured electrodes in so
far as they are traversed by the stream of elec
50
trons, is essential for the uniform formation of
60
ister or coincide exactly with the openings of
the control grid. The auxiliary grid is main
tained at the same or at a negative potential in
relation to the cathode. As a consequence, the
spaces between the grid wires act as condenser
lenses and they thus focus and concentrate the
electrons in the interstices between the wires of
the control grid. Hence, the electrons find no
chance to impinge upon the control grid proper.
as usual, is connected with a positive biasing
potential. In this manner conditions, on the
one hand, are made such that the space-charge
grid will not be struck by electrons, as is true of
Fig. 1. As a result the appreciable consumption
of energy that has so- far been inseparable from
the use of a space-charge grid and which has
proved a hindrance to the wider introduction of
this type of tube, is obviated. On the other hand, 50
the electrons through the space-charge grid can
be focussed in the openings of the control grid,
and they are there subjected to a maximum
control action.
Fig. 4 represents a cross-section through the 55
electrode system of a screen-grid tube containing
the cathode K, the control grid Go, the screen
grid Gsc, and the anode A. The two grids may
each consist, for example, of a sheet-metal cyl
inder in which are punched slots running paral 60
lel to the cathode. The two apertured electrodes
are so disposed in reference to each other that
the openings will come to register precisely. The
potential of the control grid should always be
negative in reference to the cathode. In this
manner, the openings of the control grid act like
cylindric condenser lenses, and as a result they
cause the electrons to become concentrated in
the openings of the screen grid with the conse—
quence that the screen grid can be practically
rendered “currentless”. The practical result and
success of this step manifests itself not merely in
a saving of current by the suppression of current
in the screen grid, but also in the circumstance 75
13
that the tubes become uniform,‘ contradlstinct
vfrom-‘what has heretofore'been'the case-where‘ it
was ‘largely a ' question. of ' chance'whether the
unwhes of'the-screenrgrid'would collect or‘ab
sorb electrons or not, 'wlththe ‘result: that rather
great disparities were observed inthe size'of the
currents ?owing in the screen grid. Variations
in this vregard became particularly annoying
whenever the screen-grid voltage was tapped
10 from. a voltage divider or potentiometer.
A further embodiment of the basic idea of this
invention is indicated in Fig. 5. It is well known
that in the presence of a very small distance be
tween control grid and cathode, the electrons will
not always be derived in a uniform way along the
entire surface of the cathode, indeed, that some
portions of the cathode become subject to marked
loads and that these local areas furnish practi
cally the whole electron emission, whereas neigh
boring portions would give off no electrons. This
circumstance proves unfavorable from the view
point of life of the cathode, and it imposes a
limitation so far as the slope (mutual conduc
tance) is concerned in the presence of inter
25 grid distances falling below the size of grip open
ings.
Now, another object of this invention is
a novel formation of the cathode surface such
that it will match and adhere to the equipoten
tial surfaces produced by virtue of the grid con
struction.
Fig. 5 is a longitudinal section through the
electrode system of a triode tube containing the
cathode K, the control grid Go and the anode A.
The trend or shape of the potential surfaces is
35 indicated by the horizontal solid lines. The
cathode surface has ridges or depressions the
shape of which is a function of the control elec
trode. If the latter, for instance, consists of a
3. *An electron discharge tube: comprising an
indirectly heated'cathode having a pluralityof
uniformly spaced similarly-shaped electron emit
ting surfaces, a perforated electrode positioned
adjacent said cathode vwith ‘its ‘perforations in
registry with the said-similarlyshaped cathode
emitting surfaces, and 'a'n'additional " electrode
surrounding the perforated- electrode.
4. .An' electron discharge tubercomprising 8. cy
lindrical equi-potential cathode having formed 10
on its surface a helically-grooved electron emit
ting surface of uniform pitch, a similarly pitched
helically-wound grid electrode surrounding the
cathode so that the spaces between successive
grid turns register with the grooved emitting sur 15
face, and an additional electrode surrounding
the cathode and the grid electrode.
5. An electron discharge tube comprising an
equipotential cathode having a plurality of de
pressions distributed along its length, a grid elec— 20
trode surrounding the cathode and having its
spaces aligned with the cathode depressions, and
an additional electrode surrounding the grid elec
trode.
6. An electron discharge tube comprising a 25
cathode, an anode, a grid electrode interposed be
twen cathode and anode, and means for con
trolling the electrostatic ?eld in the vicinity of
the grid electrode whereby the electron flow
therethrough will not be impeded, said means 30
comprising arcuate electron emitting surfaces
formed on the surface of the cathode and extend
ing in directions parallel to the cathode axis, the
grid electrode being in the form of rods which are
also arranged in parallel relation to the cathode
axis.
7. An electron discharge tube according to the
preceding claim wherein the spacings between the
mesh or gauze or of a punched perforated sheet
40 or lamination, the said depressions are made
grid rods are in registry with the arcuate cathode
surfaces.
40
8. An electron discharge tube comprising an
equipotential cathode having a plurality of longi
grid opening. In the case of rodlet-type grids,
45 corrugations will, in analogy, be arranged paral
lel to the axis of the cathode, as shown in Fig. 6,
while with spirally-wound grids there should be
tributed around its surface, a grid electrode pro
vided with longitudinally extending conductors
surrounding the cathode and having the spaces
between successive grid conductors aligned with
the cathode depressions, and an additional elec
trode surrounding the grid electrode.
9. An electron discharge tube comprising a
cathode, an anode, a grid electrode interposed 50
between cathode and anode, and means for con
trolling the electrostatic ?eld in the vicinity of the
grid electrode whereby the electron ?ow there—
through will not be impeded, said means compris
hemispheric (calotte-shaped) so that to each
grid mesh there corresponds a depression which
comes to be positioned exactly in the rear of the
provided a helical groove having the same pitch
as the grid.
50
Instead of providing the cathode surface with
depressions, roughly the identical effect is attain
able by making the cathode bl-partite, in other
words, a cylindrical electron-emission surface of
the kind heretofore customary, and further, at
55 close proximity in front thereof and conductively
connected therewith, a grid whose openings come
to register with those of the control electrode.
What I claim is:
1. An electron discharge tube comprising a
60 cathode, an anode, a grid electrode interposed be
tween cathode and anode, and means for con
trolling the electrostatic ?eld in the vicinity of
the grid electrode whereby the electron ?ow
therethrough will not be impeded, said means
65 comprising arcuate electron emitting surfaces
formed on the surface of the cathode, which ar
cuate surfaces are arranged in registry with the
apertures of the grid electrode.
2. An electron discharge tube comprising an
70 equipotential cathode having a plurality of de
pressions uniformly distributed along its length,
a helical grid electrode surrounding the cathode
and having its spaces between successive turns
aligned with the cathode depressions, and an ad
75 ditional electrode surrounding the grid electrode.
tudinally extending depressions uniformly dis
ing spaced electron emitting surfaces in the form 55
of narrow elongated strips formed on the surface
of the cathode and extending in directions paral—
lel to the cathode axis, the grid electrode being
in the form of rods which are also arranged in
60
parallel relation to the cathode axis.
10. An electron discharge tube comprising an
equipotential cathode having a plurality of longi
tudinally extending electron emitting strips uni
formly distributed around its surface, a grid elec
trode provided with longitudinally extending con 65
ductors surrounding the cathode and having the
spaces between successive grid conductors sub
stantially aligned with the electron emitting
strips, and an additional electrode surrounding 70
the grid electrode.
11. An electron discharge tube comprising an
equipotential cathode having a plurality of longi
tudinally extending depressions which are oxide
coated and uniformly distributed around its sur 75
4
2,130,280
face, a grid electrode provided with longitudinally
extending conductors surrounding the cathode
and having the spaces between successive grid
conductors substantially aligned with the oxide
Cl
coated cathode depressions, and an additional
electrode surrounding the grid electrode.
12. An electron discharge tube comprising an
equipotential cathode having a plurality of longi
tudinally extending oxide coated strips uniformly
distributed around its surface, a grid electrode
provided with longitudinally extending conduc
tors surrounding the cathode and having the
spaces between successive grid conductors sub
stantially aligned with the cathode strips, and an
additional electrode surrounding the grid elec
trode.
MAX KNOLL.
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