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Патент USA US2119119

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May`31, 1938.
1. sHoENBERG ET A1.
2,119,119
CATHODE RAY_TUBE
Filed Sept. 28, 1934'
2 Shee’Ls--Smsc‘ïl 1
NÁSN
, G. i. comm/FFE
BY
«
AND mFRd/VCISTEDHAM
#Q5/.M
ATTORNEY
May 31, 1938.
1. sHoENBERG ET Al.
2,119,119
CATHODE RAY TUBE
Filed Sept. 28, 1934
2 Sheets-Sheet 2
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INVEN TORS
L SHDFNBFRG, 6. E. CUNDUfFE
AND #FRANC/5 TED/‘MM
BY
Mfîfw
.
ATTORNEY
2,119,119
’ Patented May 31, 193s
ori-‘lc
UNITED STATES
2,119,119
CATHODE BAY TUBE
Isaac Shoenberg, London, George Edward Cond
. liiì'e, Buckinghamshire, and William Francis
Tedham, Abbey Wood, London, England, as
signors to Electric and Musical Industries Lim
it‘icld, Hayes, England, a. company of Great Brit
Application September 28, 1934, Serial No. '145,838
In Great Britain October 3, 1933
9Clalms.
The present invention relates to improvements
in cathode ray tubes.
-
A cathode ray tube is known which comprises
a cathode, a modulating electrode or “modu
5 lator", one or more focusing electrodes, an anode
and a fluorescent screen. Tubes of this kind are
used for purposes such as television reception,
received picture signals being applied between the
cathode and modulator so as to vary the intensity
10 of the ray reaching the screen and thus produce
positive with respect to the cathode potential and
to the decelerating electrode a potential approx
imately equal to the cathode potential, the shape
and disposition of the electrodes and the poten
tials applied thereto being such that, in opera
tion, increases of potential of the decelerator, in
the negative sense with respect to the cathode
l potential, produce increases of current to the
a corresponding variation in intensity of the
fluorescent light emanating from this screen.
There are two classes of known cathode ray
tube. The older soft types are not highly evacu
ated and the concentrating effect exerted by the
„
The aperture in the diaphragm of the deceler
ator is of the ordinary type, that is to say, it is
not obstructed by grid wires or the like extending
across it.
~
With this arrangement electrons emitted from
the cathode are slowed up to a velocity not differ 15
ing greatly from zero in a region lying in the
ions of a gas upon the electron stream serves to
focus the ray in a small spot upon the screen.
neighbourhood of the decelerating electrode and
The newer hard types are highly evacuated and
are accelerated from this region towards said
screen. Such a region will for convenience be
require electrostatic or electromagnetic focusing
20 means. The present invention relates exclusively
to the latter class of cathode ray tube.
20
referred to as a deceleration region.
In this way there has been produced a cathode
It has been found, however, that the modula
ray tube having a nearly straight characteristic,
tion characteristic curves of hard tubes, that is to
which is desirable for some purposes, and one in
say, the curves obtained by plotting modulator
volts (relative to the cathode) as abscissae
against iiuorescent screen current as ordinates,
are excessively curved, changes in fluorescent
screen current for large changes in modulator
which there is reduced change of size of the
iiuorescent spot with change in modulator volt
age. It has, however, been found that with tubes
of this kind there may be a halo of light around
the fluorescent spot. It is thus a further object
of the present invention to provide a cathode ray
volts being disproportionately large compared
30
iirst accelerator.
with the changes in fluorescent screen current
produced by smaller changes in modulator volts.
It has been found that the size of the spot
varies with the modulator volts, generally in
creasing as the potential of the modulator ap
_ proaches that of the cathode, thus giving rise`
to loss of detail in the reconstituted picture.
It is an object of the present invention to pro
vide means for at least partially eliminating the
above mentioned disadvantages.
It is another object oi.’ the present invention to
40
provide an electric circuit comprising a cathode
ray tube of the hard type having arranged within
its envelope, in the order mentioned, a cathode,
a first accelerating electrode, a decelerating elec
45 trode having an apertured diaphragm and a sec
ond accelerating electrode and a screen, the ac- .
celerating and decelerating electrodes being in
the form of electrodes, so disposed that the ray
constituted by electrons from said cathode can
pass through them to a screen associated with the
tube, the tube being provided with electrostatic
or electromagnetic means for focusing the ray in
a. small spot on the screen and with means for
defiecting the ray over the screen, and means for
55 applying to said accelerating electrodes potentials
tube in which no such halo is formed around the 30
iiuorescent spot. With this end in View an elec
tric circuit comprises a cathode ray tube of the
hard type having varranged Within its envelope
in the order mentioned, a cathode, a first ac
celerator, a first decelerator having an apertured
diaphragm, a, second accelerator, a second de
celerator, a third accelerator and a screen, the
accelerators and decelerators being in the form of
electrodes so disposed that the ray constituted by
electrons from said cathode can pass through 40
them to said screen, the tube being provided with
electrostatic or electromagnetic means for focus
ing the ray in a small spot on the screen and
with means for deñecting the ray over the screen,
'and means for applyingv to the accelerators poten 45
tials positive with respect to the potential of said
cathode and to the decelerator potentials ap
proximately equal to the potential of said cath
ode, the shape and disposition of the electrodes
and the potentials applied thereto being such 50
that, in operation, increases of potential of said
ñrst decelerator in the negative sense with respect
to the potential of said cathode, produce in
creases of current flowing to the first accelerator.
Tubes constructed in this way may have a 55
2
2,119,119
characteristic which ls curved but to a less extent
than the known tubes above referred to and the
change of spot size with modulator potential is
satisfactorily small whilst the “halo” is substan
tially absent. The relatively small but still defin
ite curvature of the characteristic which is ob
tained is advantageous for some purposes where
for example it is desired to increase the detail in
the lighter parts of the reproduced picture in
comparison with the detail in the darker parts.
Henceforth accelerating and delccerating elec
trodes will be called, for convenience, accelerators
and decelerators respectively.
Embodiments of the present invention will now
be described, by way of example, with reference
to the accompanying diagrammatic drawings, in
which
Fig. 1 illustrates a tube having two accelerators
and one decelerator arranged so that there is
20 formed, during the operation of the tube, one
deceleration region.
Fig. 2 shows a circuit arrangement for supply
ing appropriate potentials to the Various elec
trodes of a tube of the kind illustrated in Fig. 1.
Fig. 3 illustrates a tube having three acceler
ators and two decelerators arranged so that two
deceleration regions are formed during the opera
tion of the tube, and
Fig. 4 shows a circuit arrangement for sup
plying appropriate potentials to the various elec
trodes of a tube of the kind illustrated in Fig. 3.
In the embodiment illustrated in Fig. 1, a,
cathode ray tube suitable for purposes of tele
vision reception, comprises an evacuated, sealed
glass envelope consisting of a cylindrical portion
I flaring out into a frusto-conical portion 2. The
diameter and length of the cylindrical portion I
are about 11/(2 inches and 8 inches respectively
the diameter of the base 3 of the frusto-conical
«10 portion 2 is about 9 inches, whilst the overall
length of the envelope is about 19 inches.
Sealed internally to the closed end of the cylin
drical portion I is a glass tubular portion 4
which projects internally from and lies wholly
45 within the cylindrical portion I. The tubular
portion 4 is about 1/2 inch in internal diameter
and 6%.; inches in length.
Disposed within the tubular portion 4 are a
cathode heater 4A, a cathode 5, a cathode shield
6, a ñrst accelerator l, a decelerator 8 and a
second accelerator 9, these electrodes being ar
ranged within the glass tubular portion 4 in the
order mentioned. The decelerator 8 is adapted to
function as a modulator and the second accelera
tor 9 corresponds to what is sometimes known as
the first anode of the tube. Leads to the elec
trodes disposed within the glass tube 4 may
be passed through a pinch I0 sealed into the
closed end of the tubular portion I, the leads
to the cathode and its heater also serving as
supports for these electrodes whilst the cathode
shield, the two accelerators and the decelerator
are mounted as sliding ñts within the glass tubu
lar portion 4. Leads to the three last mentioned
“ electrodes pass from the pinch i0 through holes
tioned, except the heater, are of cylindrical shape
and are mounted co-axially within the envelope.
A second anode I5, in the form of a cylinder
of 31/2 inches length, is also mounted as a
sliding fit within the cylindrical portion I of the
envelope in'such manner that the second anode
overlaps the second accelerator or first anode
by about ‘A of an inch.
On the inner side of the base 3 of the frusto
conical portion 2 of the envelope is deposited
a fluorescent screen I6 of any known or suitable
material. Either electrostatic or electromagnetic
means such as two pairs of coils Il, I8 may be
utilized to deñect the ray so as to scan the
ñuorescent screen I6 and these means may be
situated, either inside or outside the tube be
tween the second anode I5 and the screen I6 and
close to the second anode.
The cathode 5 may be of any suitable kind
but preferably is in the form of a shallow open
pill-box of 1A; inch diameter, electrons being
emitted from the fiat circular base which is in
directly heated by means of the heater which lies
within the box. The cathode may be coated with
an electron emitting substance such as a mixture ~
of strontium and barium oxides.
The shield 6 is also in the form of a pill-box,
of about lé inch length and diameter, having a
central aperture I9 in its base and being disposed
around the cathode 5 so that the cathode lies
close to (but does not touch) the bottom of the
shield B and emits electrons through the aperture
I9 in the base of the shield.
The ñrst accelerator 'I is in the form of a very
shallow open pill-box; about 2 millimetres in
length and 1/¿ inch diameter. It has a central
aperture 20 in its base which is disposed about 3
millimetres away from the base of the shield 8
and the “skirt” of the ñrst accelerator is turned
toward the cathode 5.
lo
The decelerator 8 is in the form of a short
cylinder, about 1/2 inch length and 1/2 inch
diameter, with a disc (having an aperture 2|
disposed therein) disposed along its length some
what nearer the ñrst accelerator 'I than the 4.",
second accelerator 9. One end of the decelerator
8 is about île of an inch away from the ñrst ac
celerator 1.
The second accelerator or ñrst anode 9 bears
two discs, the one disposed at the end of the elec
trode lying closer to the deceleratoi1 8 having an
aperture 22, and the other being disposed about
l inch from the opposite end and having an
aperture 23.
The second anode I5 carries no apertured discs, 1 i
and a lead to this electrode may be taken through
the wall of the frusto~conical portion 2 of the
envelope.
The apertures I9, 20, 2| and 22 are all of 0.075
inch in diameter, whilst the second aperture 23
in the accelerator 9 is of 0.15 inch diameter.
The various electrodes are maintained at their
appropriate potentials by means of the'circuit
arrangement shown in Fig. 2.
An alternating potential difference of any con
venient voltage, is stepped up by means of a
transformer 34 to 5,000 volts and rect-iñed in the
device indicated generally at 35. This steady po
such as I I, I2 in the side walls of the glass tube 4
and back through holes such as I3, I4 on to the
electrodes. The second accelerator 9, about 3
inches in length, is mounted within the tubular
tential is maintained across a potentiometer re
portion 4 in such manner that l inch or more of
sistance 36, 31.
the electrode protrudes beyond the tubular por
A tapping 38 on the potentiometer is connected
both to the cathode 5 and to the cathode shield
6, these electrodes being in this manner main
tained at about 40 volts positive with respect to
tion.
If desired a lead may be taken to this pro
truding portion through the side wall of the
cylindrical portion I of the envelope instead of
75 from the pinch IU. All of the electrodes men
earth.
Tappings 39, 40 and 4I on the potenti
2,119,119
ometer are connected to the first accelerator 1,
the second accelerator 9 and the anode l5, re
spectively, in such 'manner that these electrodes
are respectively maintained at about 200 volts,
Gn
1,000 volts and 3,600 volts positive with respect
to the earth potential.
'
Where the arrangement is to be used as a
television receiver, the received signals are de
tected and amplified in a device shown generally
at 42. The output from the device d2 is applied
across a resistance 43 one end of which is earthed
and the other end of which is connected to the
decelerator or modulator 8.
It will be seen that the modulator 8 derives a
negative bias from the high tension supply to the
tube and a positive bias from the ñow of picture
signal current through resistance 43.
The re
sultant bias is such that the picture signals oper
ate to vary the potential of the modulator 8,
two electrodes acts upon the diverging cone of
electrons in much the same way as a lens acts
upon a diverging beam of light, and for this
reason the arrangement of ñrst and second
anodes may be called an “electron lens”. In the
present case the cone of -electrons which is di
verging on entering the electron lens emerges as
a converging cone and is brought to a focus upon
the fluorescent' screen I6.
It has been found that with this arrangement
a spot of very small size can be obtained upon the
screen and that changes in size of the spot, with
changes in modulator volts, are less than the
corresponding changes which have been observed
in tubes of known kind.
In a second embodiment of the invention the
shield B, shown in broken lines in'Fig. l, may be
omitted and the catho'de 5, together with its
heater, moved up towards the first accelerator 1
relative to the cathode, from zero down to about I so that there is about 1A; inch between the base of 20
the first accelerator and the base of the cathode 5.
-30 volts, at which voltage the ray is extin
The iìrst accelerator 1 is in this case main
guished.
tained at about 10 volts positive with respect to
The potentials above given have been so se
lected in relation to the shape and disposition of the cathode whilst all other electrodes are main
the electrodes that increases in potential of the
decelerator 8 in the negative sense produce in
creases in current flowing to the ñrst acceler
ator 1.
It is believed that the operation of the tube is
somewhat as followsz-
.
Referring more particularly to Fig. 1, electrons
emanate from the cathode 5 with random veloci
ties and directions. The electrostatic accelerat
ing ñeld existing between the positive i’lrst ac
' celerator 1 on the one hand and the earthed
cathode 5 and shield 6 on the other hand has the
effect of extracting a large number of electrons
from the cathode and concentrating these elec
trons so as to pass through the aperture’ 2l in'
40 the decelerator 8.
The decelerator is at a negative potential with
respect to the first accelerator 1 so that between
these two electrodes the electrons are deceler
ated and a deceleration region is formed close to
the aperture 2l in the decelerator 8.
The second accelerator 9 is at a high positive
potential with respect to the decelerator 8 and
the accelerating field which exists between these
two electrodes extends into the deceleration re
gion of the tube. The velocities (in the direction
of the axis of the tube) with which the electrons
emerge from the cathode 5 are small compared
to the axial velocities which they subsequently
acquire owing to the electrostatic accelerating
Si .wi ñeld existing between the various electrodes, and
electrons which emerge from the cathode with
comparatively large transverse velocities (say up
to 0.2 volt) are to a very large extent filtered out
by the decelerator 8 so that the electrons drawn
from the deceleration region toward the second
accelerator 9 have almost the same axial and
radial velocities and hence can be brought to a
very sharp focus on the iiuorescent screen I6.
The focusing is eiîected in the following manner.
Between the deceleration region and the dis
tant end of the second accelerator or first anode
9 the electrons tend to diverge owing to the
shape of the electrostatic iields produced between
the electrodes.- On reaching the comparatively
strong electrostatic ñeld maintained between the
adjacent ends Iof the ñrst and second anodes,
however, the diverging electrons are concentrated
or focused back on to the axis of the tube and
at the same time accelerated towards and through
75 the second anode l5. The ñeld between these
tained at the' potentials specified for the last
described embodiment.
An accelerating field exists between the cath
ode and first accelerator 1 so that electrons are
accelerated towards the first accelerator, some
electrons passing through the aperture in this 30
electrode.
Between the ñrst accelerator and decelerator
the electrons are decelerated as they approach
the deceleration region which, as before, lies in
the neighbourhood of the aperture in the de
celerator.
„
The ñrst and second anodes operate, as in the
last described case, to accelerate and focus the
electrons upon the fluorescent screen.
In the second embodiment described above the
ñrst accelerator 1 is at a positive potential with
respect to the cathode 5, so that many electrons
which in the embodiment ñrst described pass
through the aperture I9 in the shield 6, are in
the second embodiment attracted towards and 45
collected upon the first accelerator 1 so that a
ñuorescent spot of comparatively weak intensity
is formed upon the screen I6.
Because of this
the first embodiment is to be preferred.
It has been found that although with the two 50
embodiments described above the change of spot
size with modulator (or decelerator) volts is less
than that obtained with known tubes, the spot
possesses a halo of light. In the embodiment
illustrated in Figs. 3 and 4, however, this disad 55
vantage is almost entirely eliminated.
The tube illustrated in Fig. 3 is of the same
general form as that illustrated in Fig. 1 but in
cludes an extra decelerator and an extra acceler
ator. Thus within the glass tube 24, which corre 60
sponds to the tube d of Fig. 1, there are disposed,
'in the order mentioned, a cathode heater 24A, a
cathode 25, a shield 26, a iirst accelerator 21,
a ñrst decelerator 28, a second accelerator 29, a
second decelerator 30 and a third accelerator or
ñrst anode 3l. A second anode 32 is mounted
as a sliding ñt in the cylindrical portion of the
envelope.
The cathode, shield and ñrst and second anodes
are of the same form as those illustrated in Fig. 1. 70
The ñrst accelerator 21 is in the form of an open
pill box of 0.04 or 0.08 inch height, its base, which
has a central aperture, being turned away from, '
and being disposed about 0.08 or 0.12 inch from,
the base of the shield 25. The first decelerator 75
4
2,119,119
23. which may be utilized as a. modulator, is also
in the form of an apertured open pill box of
about 0.08 or 0.12 inch height, its hase being
turned away from and being disposed about 0.12
or 0.16 inch from the base of the lirst accelerator
21. 'I‘he second accelerator 29 is of exactly the
same size and shape as the ñrst accelerator 21;
its base is turned away from and is`disposed about
`0.08 or 0.12 inch from, the base of the first de
celerator 28. 'I'he second decelerator 30 is in the
form of a short cylindrical tube having a cen
trally apertured disc disposed within it at a point
somewhat nearer the end which is adjacent
(about 0.04 inch from) the second accelerator 29
than the other end which is disposed about 0.04
inch from the third accelerator or first anode 3i
The apertures in the shield, accelerators and
decelerators are all equal to about 0.08 inch di
ameter and the diameters of these electrodes
themselves are all equal to the diameter of the
first anode.
As before, appropriate potentials are applied
to the electrodes from a common potentiometer
resistance 44, 45 across which is maintained a
steady potential difference of 5,000 volts. Rela
tive to earth potential the cathode 25, cathode
shield 26 and second decelerator 30 are all main
the density of the current flowing through the
tube and the improvement in the constancy and
definition of the fluorescent spot is believed to be
due to the fact that the second decelerator 3l is
not at a negative potential with respectio the
ca_thode 25.
In the tube illustrated in Figs- 3 and 4 modu
lation of the ray may be effected by varying the
potential relative to the cathode, of the shield 2l
or of either of the decelerators 2l and 3l, the
potentials of those two of these electrodes not
used for modulation being held at approximately
cathode potential.
-It is not essential that the ñrst and second ac
celerators 2l and 29 should be maintained at the
same potentials relative to the cathode. It may.
for instance, be convenient to keep either or both
of.' them at the same potential as the first anode
3 .
The number of deceleration regions formed in 20
the tube may be greater than two, the formation
of each such region being achieved by the intro
duction of an extra pair of electrodes, one serv
ing to accelerate the electrons and the other
serving to decelerate them.
A magnetic electron lens may be used to assist
in forming a focused spot upon the fluorescent
tained at about 40 volts positive, the first and f screen in place of the electrostatic electron lens `
second accelerators 21 and 29 respectively at described above. Moreover a magnetic electron
30 about 250 volts positive, the third accelerator 3i
lens may be used to assist in concentrating the
at about 1,000 volts positive and the second anode electrons in the neighbourhood of the decelera
at 3,900'volts positive. Received picture signals tion region, the final focusing on the fluorescent
are used to modulate the intensity of the ray in screen being then achieved by means of another
a manner similar to that described in connection
electron lens.
with Figs. 1 and 2, bias for the tube being derived
partly from the high tension supply and partly
from the iiow of picture signals through a re
sistance 46 inserted in the output circuit of a
radio receiver 41. The arrangement is such that
40 the picture signals are effective in varying the
potential of the first decelerator or modulator
28, relative to the cathode, from zero down to
about -30 volts at which voltage the ray is ex
tinguished. Over this range of modulator volts
45 no halo and only a small change of spot size is
observable.
As before, the potentials applied to the elec
trodes are such that an increase in the potential
of the decelerator 28 in the negative sense pro
50 duces an increase in the current flowing to the
first accelerator 21.
During the operation of the tube shown in
Figs. 3 and 4, two deceleration regions are
formed. Electrons are extracted from the cath
55 ode 25 by the relatively positively charged first
accelerator 21 and are focused upon the aperture
in the modulator or first decelerator 28. The
potential of the modulator varies from zero to
_30 volts relative to the cathode, so that the
60 electrons are slowed up as they approach a. de
Ii sharp focusing of the ray is not essential
the second anode of either of the tubes illus
trated (shown in broken lines in the iigures) may
be omitted.
The characteristic curve of a cathode ray tube
can generally be represented by the equation
IAZKEQI, Where K represents a constant, In rep
resents the ñuorescent screen current and E¢
represents modulator voltage. For the tube just
described :z: is equal to about 1.8, whilst for most
known tubes :r has a value of 2 or more and for 45
the tube illustrated in Fig. 1 :n is equal approxi
mately to unity.
'
Over the greater part of the useful current
range of the tubes described above the intensity
of fluorescence is substantially proportional to
the intensity of the current ñowing to the iiuo
rescent screen, so that in the equations given
above IA may be taken as representing the in
tensity of fluorescence as well as the fluorescent
screen current.
The index, or “I” figure in the above equations
therefore determines what may be called the
“intensity-contrast” of the tube. An apprecia
tion of what is meant by the expression “inten
sity-contrast" may be gathered from the follow
celeration region near the aperture in the ñrst
ing considerations:
decelerator 28. From this point the electrons are
It has long been recognized in the cinema art,
that if the brightnesses of all points of an image
accelerated towards the second accelerator 29 and
are focused upon the aperture in the second de
celerator 30. This decelerator has the effect of
again slowing up the electrons as they approach
a, second deceleration region which lies in the
neighbourhood of the second decelerator 30. The
ñrst and second anodes 3| and 32 co-operate to
gether in accelerating electrons from the second
deceleration region and focusing them upon a
fluorescent screen 33. The satisfactory operation
of the tube described is dependent upon the rela
tive potentials of the various electrodes, their
separation, the sizes of the apertures in them and
viewed on a fiat projection screen are propor
tional to the brightnesses on the object from
which the images are derived, the screen image
appears flat and lminteresting to the eye. This
effect is believed to be due to the fact that the
images are projected in black and white and the
additional effect of detail which would be given
to the lighter parts of the picture by the natural
colour is absent.
It is therefore common prac-v
tice in the cinema industry to develop picture
films in such manner that detail in the lighter
or less opaque portions of the positive nlm pic
55
2,119,119
tures is brought out, or ampliñed as it were, rela
5
supply, means for supplying positive potentials
tively to the detail in the darker or more opaque , relative to the cathode to the second accelerator
portions of the pictures. A ñlm developed in this
way, and the images projected from it, are said to
possess “intensity contrasts" of value greater
than unity and the images derived from the film
are more pleasing and appear more full of detail
than images projected from a ñlm of intensity
contrast equal to unity, that is to say, a film in
which the light transmitted through all points is
exactly proportional to the brightnesses of the
corresponding object points.
It is found in fact that a ñlm developed to
an intensity contrast of from about 1.8 to 2.0 is
most satisfactory in this respect.
Similarly a tube having an intensity contrast
greater than unity is one‘which amplifles signals
of large amplitude to a greater extent than it
does signals of small amplitude and a tube hav
20 ing-an intensity contrast of unity is one which
produces no amplitude distortion.
_
“ 3. An electric circuit comprising a cathode ray
tube, comprising a cathode, an apertured shield l()
electrode, an apertured accelerator electrode, an
apertured decelerator electrode, a second aper
tured accelerator electrode, an anode and a
screen, means for supporting said electrodes pro
gressively in register with said cathode, a power
supply, means for supplying positive potentials
relative to the cathode to the second accelerator
electrode, means including a resistance for main
taining the decelerator electrode at a potential
negative with respect to the cathode, means to 20
supply signalling voltages across the resistance,
1f now the signals received at a cathode ray
and means to vary the potential of the first
tube receiver are truly representative of the tone
value- of 'the object, that is to say, are trans
mitted with an effective intensity-contrast of
unity, then, since the reproduced images' are to
accelerator electrode with respect to the cathode
in accordance with the signalling voltages sup
_ be viewed upon a screen, the receiver tube should
have an intensity-contrast higher than unity and
usually in the neighbourhood of 1.8, because this
is usually found to be the intensity-contrast
which appears most pleasing to the eye. On the
other hand if the signals are transmitted with an
effective intensity contrast greater than unity
(say, for example, are derived from a motion
35 picture ñlm developed in the usual way so as to
have an intensity-contrast of about 1.8, then the
tube at the receiver should vhave an intensity
contrast of about unity.
A tube having an intensity-contrast of 2.0 or
40 _higher is rarely of use, however.
plied to the resistance.
4. An electric circuit comprising a cathode ray
tube having arranged within its envelope a
cathode, a iirst accelerator apertured electrode,
a ñrst decelerator apertured electrode, a second
accelerator apertured electrode, a second de. 30
celerator apertured.- electrode, and a third ac-`
celerator apertured electrode, an anode and a
screen, means to support progressively all of the
electrodes in register with the cathode, means to
maintain the three accelerator electrodes at a
potential positive with respect to the cathode,
means including a resistance for maintaining the
first decelerator electrode at a potential negative
with respect to the cathode, -means to maintain
the second decelerator electrode at a predeter 40
In the embodiments of. the present invention
which have been described above it is found that
if the potential on the modulator be increased
negatively with respect to the cathode, the cur
rent ñowing to the ñrst accelerator increases in
mined potential with respect to the cathode', and
such a way that on plotting ñrst accelerator cur
rent vas ordinates and modulator volts as abscissae
cathode, a first accelerator apertured electrode, a
ñrst decelerator apertured electrode, a second
accelerator apertured electrode, a second de
celerator apertured electrode, and a third ac
a roughly straight line of negative slope is ob
tained over the working range (0 to _30) of
50 modulator volts.
The values given for the various members
of the circuits illustrated in Figs. 2 and 4 are by
way of example and should not be regarded as
55
electrode, a resistance connected in series with
the power supply and the iirst accelerator elec
trode, means including a resistance to maintain
the decelerator electrode at a potential negative
with respect to the cathode, and means to supply
signalling potentials across the resistance.
strictly limiting values.
We claim:
1. An electric circuit comprising a cathode ray
tube, comprising a cathode, an apertured shield
, electrode, an apertured accelerator electrode, an
apertured decelerator electrode, a second aper
60 tured accelerator electrode, an anode and a
screen, means for supporting said electrodes pro
gressively in register with said cathode, means for
applying potentials positive with respect to the
cathode to both of said accelerator electrodes,
65 means including a resistance to maintain the
decelerator electrode negative with respect to the
cathode, and means for supplying signalling po
tential across the resistance.
2. An electric circuit comprising a cathode ray
70 tube, comprising a cathode, an apertured shield
electrode, an apertured accelerator electrode, an
apertured decelerator electrode, a second aper
tured accelerator electrode, an anode and a
screen, means for supporting said electrodes pro
gressively in register with said cathode, a power
means to supply signalling voltages to the re
sistance.
5. An Aelectric circuit comprising a cathode ray
tube having arranged within its envelope a
celerator apertured electrode, an anode and a 50
screen, means to support progressively all of the
electrodes in register with the cathode, means
for maintaining the three accelerator electrodes
at a potential positive with respect to the cathode,
means including a resistance for maintaining the
ñrst decelerator electrode at a potential negative
with respect to the cathode, means for supplying
signalling voltages to the resistance, and means
for varying the potentials supplied to the iirst and
second accelerator electrodes in accordance with 60
the signalling voltage supplied to the resistance.
6. An electric circuit comprising a cathode
ray tube having arranged within its envelope a
cathode, a first accelerator apertured electrode, a
first decelerator apertured electrode, a second
accelerator apertured electrode, a second decel
erator apertured electrode, and a third accelera
tor apertured electrode, an anode and a screen,
means to support progressively all of the elec
trodes in register with the cathode, means -for
maintaining the three accelerator eiectrodes at
a potential positive with respect to the cathode,
means including a resistance for maintaining the
first decelerator electrode at a potential nega
tive with respect to the cathode, means for sup
6
2,119,119
plying signalling voltages to the resistance. and
resistance means for varying the potentials sup
plied to the ñrst and second accelerator elec
trodes in accordance with the signalling voltage
supplied to the resistance.
'7. An electric circuit comprising a cathode
ray tube having arranged within its envelope a
cathode, a first accelerator apertured electrode,
a ñrst decelerator apertured electrode, a second
accelerator apertured electrode, a second de
celerator apertured electrode, and a third doubly
apertured cylindrical accelerating electrode, an
anode and a screen, means to support progres
sively all ol the electrodes in register with the
cathode, means to maintain the three accelera
tor electrodes at a potential positive with re
spect to the cathode, means including a resist
ance for maintaining the ñrst decelerator elec
trode at a potential negative with respect to the
cathode, means to maintain the second decelera
tor electrode at a predetermined potential with
respect to the cathode, and means to supply sig
nalling voltages to the resistance.
8. 'I'he method of overcoming the halo eiîect
in cathode ray tubes, wherein is provided a.
source of electrons, comprising the steps of ac
celerating the electrons from said source, devel
oping signalling energy, decelerating the elec
trons in accordance with the developedsignal
ling energy, reaccelerating the electrons, and
varying the rate of reacceleration in accord
ance with the signalling energy.
9. The method of overcoming the halo eiîect
in cathode ray tubes wherein is provided a source 10
of electrons, accelerating the electrons from
said source, developing signalling energy, de
celerating the electrons in accordance with the
developed signalling energy, reaccelerating the
electrons, simultaneously varying the rate of 15
acceleration and reacceleration _of the electrons
in accordance with the signalling energy, sub
sequently decelerating the electrons, and accel
erating the electrons, and directing said electrons
upon a viewing surface.
ISAAC SHOENBERG.
GEORGE EDWARD CONDLIFFE.
W'ILLIAM FRANCIS TEDHAM.
20
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