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Патент USA US2405763

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Aug. 13, 1946.
I
I
D. HéSLOAN
Original Filled Nov. 4, 1940
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2,405,763
VACUUM TUBE UTILIZING CAVITY RESONATORS
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Aug. 13, 1946.
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Patented Aug. 13,‘ 1946
2,465,763
UNITED STATES ‘ATENT‘ OFFICE
2,405,763
VACUUM TUBE UTILIZING CAVITY
RESONATORS
David H. Sloan, Berkeley, Calif., assignor to Re
search Corporation, New York, N. Y., a corpo
ration of New York
Original application November 4, 61940, ‘Serial No.
364,284. Divided and this application June 9,
1941, Serial No. 397,236
11 Claims. (C1. 315-5)
This invention relates to electronic tubes, and
particularly to tubes adapted for the production
and modulation of ultra-high frequency oscilla
tions, i. e., oscillations of frequencies of the order
of 1,060 megacycles. This application is a divi
sion of my prior application Serial No. 364,284,
2
to circuits of low relative radio-frequency resist
ance of high impedance, so that excessive energy
will not be required to swing them through the
necessary range of control voltages; fourth, ?xed
relationship between the various elements, irre
?led November 4, 1940.
spective of temperature or ordinary shock, so
The progress of electronic and radio develop
ment since the inception of the art has been
marked by two steady advances. One of these
advances has been toward higher power, and
the other toward higher frequencies. The latter
line of advancement has been, to a certain extent
at least, incompatible with the ?rst, since with
is tuned will not be affected by relative changes
of position; ?fth, minimum undesired or “inci-.
dental” radiation from the various elements of
the tube and its auxiliaries; sixth, a minimum
of insulating material subjected to high-Fire
increasing frequency the effect of interelectrode
capacity has become greater and more trouble
that the frequency to which the device as a whole
quency ?elds. To these may be added the sec
ondary requirements of demountability for re
placement of ?laments, facility in water cooling
and avoidance of hot spots, and ease of tuning.
From the conventional approach these require
ments are incompatible to a large degree. A high
tionary process consisting in large degree of re
degree of control requires close spacing of cath
?nement in detail, which has enabled the vac
uum tube art to keep pace with the increasingly 430 ode and grid, which leads to high interelectrode
capacity. Rigid structure ordinarily means mas
rigid demands of the manufacturers and oper
some. Nevertheless, up to the last few years, the
difficulties have been met by a steady evolu
ators of transmitting and receiving apparatus.
sive structure, which again leads to high inter
electrode capacity. Water cooling systems tend
The attempt within recent years to carry the
to form effective antennae, leading to large stray
useful spectrum into the range of wavelengths in
the range of a meter and less has involved di?i 25 power radiation. The broad purpose of my in
vention is therefore to reconcile these and other
culties of a new order of magnitude. For one
apparent incompatibles.
thing, the frequencies involved are so high that
the transit time of an electron stream across the
interelectrode spaces of the tubes becomes an
appreciable fraction of a cycle. For another, even
with connecting leads reduced to minimum
lengths, their inductance has been suf?cient so
that the capacities required in tuning them to the
desired frequencies are small in comparison with '
Pursuant to this general purpose, among the
objects of this invention are: to provide a tube
which is capable of producing many kilowatts of,
power at extremely high frequencies; to produce
a high frequency generator of great frequency
stability; to produce a high frequency ampli?er
and oscillator tube of relatively high efficiency,
the interelectrode capacities in conventional tube
structures and these capacities have therefore
become not merely a nuisance, limiting the ef?
ciency of operation, but frequently an absolute
and particularly to produce such a tube wherein
the losses due to undesired radiation from the
tube itself are reduced to negligible proportions;
to produce a high frequency oscillator and am
need for a tube which will meet the severe re
tolerances demanded by the frequency of opera
tion and to maintain those tolerances under the
changes of temperature produced by such opera
tion; to provide an electronic tube of the char
acter described which may be fully ?uid cooled
and wherein the cooling system does not intro
duce material parasitic radiation of radio-fre
bar to such operation; so much so, in fact, that 4-0 pli?er which may be tuned to operate at any
desired frequency throughout a reasonably wide
it has been only with tubes of very small size and
range; to provide a high frequency oscillator and
consequent small power output that operation
ampli?er which may be constructed with the high
has been obtainable at all.
degree of accuracy required to meet the close
There therefore exists at the present time a
quirements of producing large power outputs by
generation or ampli?cation at extremely high
frequencies. These requirements are ?rst, a
cathode-grid structure which will effectively
modulate an electron stream Without the appli
cation of excessive control voltages; second, a
cathode-grid structure whose capacity and in
ductance relationships are so proportioned that
they may be tuned to the high operating fre
quency power; to provide a high power oscillator
and ampli?er tube which is readily demountable
for replacement of ?laments; to provide means
quencies desired; third, a structure lending itself 5,5 of density-modulating an electron stream at
ultra-high frequencies, in order to produce ex
2,405,763
3
tremely short bursts of electron emission occur
ring at the peaks of the oscillation and of sub
stantially uniform velocity, whereby the con
version of energy into high frequency power oc
curs at high e?iciency; to provide atype of struc
ture for high frequency electronic tubes which
is of great ?exibility, and which will, because of
4
mounting the cathode in the region of sharpest
curvature. One of the best ways of obtaining
such a structure is to form the grid of pairs of
cylindrical surfaces whose axes are parallel to
,the plane of the anode, and to'make the cathode
as a ?lament or strip having a ?at or slightly
concave face lying between the cylindrical sur
faces of the grid. This results in the lines of
such ?exibility, permit the construction of tubes
force from accelerator or anode normally ter
exactly adapted to a large variety of powers and
minating in the grid structure, none of them
services; to provide a novel and e?ective method 10 reaching the cathode, from which emission is
of tuning apparatus of the character described;
therefore normally suppressed. A few volts rela
and to provide a type of. electrode support ‘for
tive change in potential of the cathode, as re
high frequency electronic devices which is mas
ferred to either accelerator or control grid, re
sive and rugged, and which, at the same time,
sults in some of the lines of force from the ac
15
does not introduce interelectrode capacities which
celerator terminating in the cathode surface.
either severely limit the frequencies upon which
which is accordingly subjected to an extremely
the device is operative or the power which may
powerful ?eld causing very large emission to the
be developed at such frequencies.
My invention possesses’ numerous other objects '
anode;
The result is what may be termed an
“explosive” type of emission, giving electron
and features of advantage, some of which, to 20 bursts of high density for very short periods at
gether with the foregoing, will be set forth in the
the peaks of the cycles. It will be evident that
following description of speci?c apparatus em
this structure results in a relatively high capacity
bodying and utilizing my novel method. It is
as between cathode and grid, but the tuned trans
therefore to be understood ‘that my method is
mission line support enables this capacity to be
applicable to other apparatus, and that I do not
effectively resonated with an inductance as small
limit myself, in any way, to the apparatus of the
present application, as I may adopt various other
apparatus embodiments utilizing the method,
within the scope of the appended claims.
The tube of my invention involves two basic so
concepts. The ?rst, of these comprises forming
electrode supports of sturdy coaxial metallic cyl
inders which constitute a radio-frequency trans
as may be desired and still form a sharply tuned,
high Q circuit whose high resonant input im
pedance may appear as resistive, capacitive or
inductive, as the conditions of operation may re
quire.
Referring to the drawings:
Fig. 1 is a longitudinal section through a high
frequency oscillator tube embodying my inven
mission line of at ‘least one and preferably a plu
tion, the particular tube illustrated employing
rality of quarter wavelength electrical links, with 35 a radial arrangement of ?laments and grids.
impedance irregularities at or near certain of
Fig. 2 is a transverse section of the tube of
the quarter-wave points, the electrodes them
Fig. 1, showing the multiple coaxial grid-?lament
selves forming a portion of these transmission
lines as considered electrically. ‘Means are pref
supports, and water connections for cooling the
?lament mounting, the plane of section being
erably provided for varying the position of the 40 on the line 2-2 of Fig. 1.
impedance irregularities to provide exact tuning,
Fig. 3 is a transverse section through the anode
but this is not essential since, as will hereafter be
structure of the tube, the plane of section being
shown, by a proper combination of the charac
indicated by the line 3-3 of Fig. 1.
teristic impedances of the quarter-wave sections
Fig. 4 is an enlarged detailed view illustrating
and their terminating impedances, it is possible
water-cooling connections from the exterior of
to make the radio-frequency impedance of the
the tube to the ?lament mounting.
supports as viewed from the electrodes themselves
Fig. 5 is a schematic sectional view through
extremely high, so that the overall effect is al
?laments, control grid, accelerating grid, bound
most as though the electrode capacities together
ary grid, and anode of the tube.
with the inductances required to resonate them 50
Fig. 6 is a sectional View through the grid sup
were supported freely in the space within an un
port line, showing the radio-frequency by-pass
broken metallic shield. This latter feature is
between accelerating and boundary grids and the
secured by providing multiple coaxial line sections
tuning mechanism for isolating the control grid
forming branch paths of greatly different im
and water cooling the same.
pedance, certain of these paths acting as by 55
Fig. 7 is an enlarged detail showing the method
passes of negligible impedance at points where it
of insulating certain of the supporting rings upon
is necessary that some circulating currents
which the coaxial electrode elements are car
should ?ow. although D.-C. insulation must be
ried.
'
maintained, while at the same time maintaining
Fig. 8 is a section taken at right angles to the
the high impedance desired in other pathswhich 60
view of Fig. 1, and showing the anode-support
would otherwise lead to radiation. By placing
ing, cooling, and tuning system.
these by-pass sections at current nodes, the PR
Fig. 9 is a perspective view of the accelerator
losses therein may be made too small to need
grid.
consideration.
Fig. 10 is an elevation of the control-grid struc
The second fundamental concept comprises
mounting on the ends of’such supports, prefer
ture.
ably in biaxially symmetrical con?guration, one
Fig. 11 is a sectional view, taken on the plane
or a plurality of cathode-grid combinations which
between the ?lament and grid structures, and
actkas before stated, as the termini of the trans
showing in detail the ?lament support.
mission lines formed by the supports; mounting
Fig. 12 is a fragmentary axial section taken on
the grid opposed to an anode or other accelerat
the line I2-I2 of Fig. 11.
ing electrode in such manner as to produce an
Fig. 13 is an elevation of the active face of the
electrostatic ?eld between grid and accelerator
anode.
which comprises lines of force very sharply curved
Fig. 14 is a fragmentary section of the anode,
in the immediate neighborhood of the grid; and
2,405,763
5
the plane of section being indicated by the line
M-M in the preceding ?gure.
Fig. 15 is an elevation of the boundary grid.
Fig. 16 is a sectional View taken on the line
Iii-l6 of Fig. 15, and showing a portion of the
6
l which is grooved to receive tightly the end of a L
tubular anode housing 2. This housing ?ts an
internal recess or counterbore in an annular grid
?ange 3, clamping a boundary grid 4 between the
housing tube 2 and the ?ange 3. A rabbet on the
outer periphery of the ?ange 3 receives one end
Fig. 17 is an elevation of one of the ?laments.
of a main support cylinder 5, whose? other end
Fig. 18 shows a modi?ed form of coaxial line
terminates in another annular ?ange 1. All of
structure for grid-?lament support in a tube gen
the
parts thus far mentioned are of metal, and
erally similar to Fig. 1, but adapted for use either 10
I have found it convenient to make the ?anges
as an ampli?er or an oscillator with inductive
of steel, and the tube 5 also of seamless steel
feed-back.
tubing, while the cylinder 2 may be either chrom
Figs. 19, 20, and 21 are sectional views through
ium or copper plated steel or solid copper, with
the tube of Fig. 18, taken on the lines numbered
copper preferred, since it forms a portion of a
in accordance with the ?gures.
15 resonating circuit. Carrying on from the ?ange
Fig. 22 is a longitudinal section through a tube
l is a glass or “Pyrex” cylinder 9 which abuts a
built in accordance with this invention but where
terminal ?ange‘ l0.
in a cylindrical, rather than a radial ?lament
As has been mentioned already, the device as
grid and anode arrangement is used.
'
a whole is fully demountable. The ends of the
Figs. 23, 24, and 25 are transverse sections
tubes contact the ?anges with smooth machine
through the tube of Fig. 22, taken on the lines
?ts. The joints thus formed are sealed by ap
indicated by the respective numerals.
plying thereto ordinary wide elastic bands as in
Figs. 26 and 2'7 are detailed views indicating
dicated by the reference characters ll, these
the tuning mechanism for the tube of Fig. 22.
bands being smeared before application with a
Fig. 28 is a longitudinal section on a larger
25 small amount of vacuum line stop-cock grease.
scale through the ?lament support of the tube
It may be pointed out at this time that all of
of Fig. 22.
the structure thus far described with‘ the excep
Fig. 29 is a transverse section through the sup
tion of the terminal ?ange ii] is at D.-C. ground
porting columns of the tube of Fig. 22, showing
potential, and as will later be shown in detail
the construction of the centering mechanism, the 30 that
the entire exterior structure is substantially
plane of section being indicated by the line 23-29
at, radio-frequency ground. This means that the
of Fig. 28.
anode in elevation.
‘
Fig. 30 is a. sectional view taken on the line
insulating section formed by the cylinder 9 is not
subjected to R.-F. ?elds. It also renders easy
30—30 of Fig. 22.
Fig. 31 is a fragmentary section taken on the 35 the support of the device by any desired external
means. Part of such support may be the con
line 3l—3l of the preceding ?gure, showing the
nection to the pump, which is by a pipe I 2 of
passage of the cooling pipe past the anode and
relatively large interior diameter, Welded or oth
between the two sections of ‘the ?lament support.
erwise secured into the bottom of the anode hous
Fig. 32 is an impedance diagram for an open
ing 2. This pipe is not shown in Fig. 1, but is
ended, half wavelength section of transmission 40 clearly
visible at the bottom of Fig. 8.
line.
.
In the ensuing speci?cation the invention will
?rst be described in its various aspects as applied
to an oscillator tube of moderate power (i. e., ap
proximately 10 kw. peak output at 20 to 40 cen
timeters wavelength). Following this there will
be described two modi?cations illustrating respec
tively the application of the principles of my in
vention to a similar tube adapted for ampli?ca
tion or for generation of oscillations by induc
tive feed-back, and to a somewhat higher output
device. showing the principles as applied to a tube
constructed with cylindrical rather than radial
arrangement of electrodes.
The tube shown in longitudinal section in Fig.
1 is of the demountable, constantly pumped type,
as in fact, are all of those herein described, al
though the principles involved are not limited for
use in such tubes. From the structural point of
view the tube comprises a series of ?anges con“
nected by sections of tubing and held together'in
compression. From a practical point of view it
is advantageous to have the ?anges pierced for
and held by circumferential bolts to hold the parts
firmly in position when the tube is not under vac
uum, but when in use the external air pressure
tends to hold the entire device together, and the
tube has actually been operated without the re~
taining bolts; these have therefore been omitted
in the drawings since they add a further com
plexity of detail to an already complex structure.
Considering for the moment, therefore, only
the external structure which forms the housing
and which supports the remainder of the equip
ment, the tube comprises an anode housing flange
The various elements which contribute to the
electronic action of the tube are mounted within
the envelope thus formed on columnar supports
each of which has transmission line characteris
tics designed to meet its particular function.
These elements are shown in schematic arrange
ment in Fig. 5, and comprise an anode IS, a
boundary grid 4, an accelerating grid I5, a control
grid l6, and a ?lamentary cathode ll.
Fig. 5 is drawn to a greatly enlarged scale and
shows a fragmentary section of the elements co
operating with a single ?lamentary cathode. _In
the tube h'ere shown six such cathodes are used
and the portions shown of the other elements are
repeated for each cathode. One advantage of
the type of structure here shown is that the abil
ity of the tube to supply power output varies al
most directly as the number of ?laments used,
and that the changes required to add additional
?laments are relatively minor.
Tubes have been
designed conforming substantially to the struc
ture here shown with as high as twenty-four ?la
ments, each with its attendant grid-anode struc
ture, but since each of these assemblies is merely
the duplicate of the others as far as performance
is concerned, it is sui?cient for the present to con
sider one only.
Considering, therefore, the portion of the ele
ments shown in Fig. 5, the anode I3, preferably
made of high conductivity oxygen-free copper, is
operated at the maximum potential of the sys
tem, say 10 to 50 thousand volts positive. It is
provided with a V-shaped groove 2!] with its axis
parallel to the axis of the ?lament. Next, pro
ceeding toward the ?lament, is the boundary grid
2,405,763
7
4, which is also. preferably made of‘ oxygen-free
copper. This: is provided; with an aperture sur
8
trons can and do traverse it- in a reasonably
small fraction of a cycle.
The biasing potential between cathode’ and
rounded by a collar 2 l' in accurate alinement with
grid is so adjusted that emission can occur only
the groove 20 in the anode. Next in line is the
for an instant at the cycle peaks, and cut-o? may
accelerator grid 15, with an aperture 22 which is
occur even before the ?rst electrons emitted have
somewhat narrower than the opening in the
traversed the space charge region. Furthermore,
boundary grid, and which is'operated at a poten
while in this region there is a maximum differ
tial. above the cathode of from 5 to 20 thousand
ence of velocity as between electrons, both by
volts. Allpotentials mentioned are illustrative
reason of differing initial velocities of emission
10
and relative only, since the actual values used will
and, more important, by reason of differing ac
depend upon the size, power output and operating
celeration due both to phase of emission and ?eld
frequency of the device. Furthermore, modi?ca
strength
at various parts of the cathode surface.
tions in design are possible whereby the functions
The important point is that because the re
of certain of the grids are combined, other elec
gion is so shallow all of the electrons emitted do
trodes are operated at ground potential, etc.
get through it before the cycle has advanced too
Such modi?cations will be considered later; the
far and, having traversed it, fall into the region
purpose here is to show the application of the
of high potential gradient where acceleration to
principles of my invention to the present tube.
ward the anode is very great; space charge ef
The most important portion of the combina
tion is the arrangement of the cathode-grid 20 foot is of no further moment, and they receive
so large a portion of their ?nal velocity that their
structure. The important features here are ?rst,
differences of velocity in the initial region are
that the control-grid elements comprise parallel
immaterial.
cylindrical surfaces, curved as they are presented
It should be realized that while space-charge
to the ?lament. In the present case they are rods
effect
prevents some emission and decreases the
25
or wires, but they could be cylindrical surfaces
acceleration
of electrons ‘emitted, it will not drive
formed as the edges of a slot in a flat plate with
those which have been emitted back to the cath
out affecting their performance. Between these
ode nor prevent their reaching the anode. It
surfaces, and slightly back of the plane of their
follows that the space-charge region may be con
centers of curvature, lies the ?lament, which has
a ?at or preferably a slightly hollow ground face 30 sidered as a reservoir for emitted electrons. With
conventional grid-cathode structures it is rela
presented to the anode. It is convenient to op
tively deep, so that, at the frequencies and pow
erate'the ?lament at ground potential (disregard
ers at ‘which this tube is intended to operate,
ing for the moment the slight voltage drop along
transit therethrough occupies a major portion
the ?lament) and, for the powers here consid
of the cycle, and with the varying velocities ob
ered, to operate ‘the grid [6 at 200 to 500 volts
taining while in this region the electrons strag
negative.
gle through to reach the anode in such varying
It will be‘ seen that at the orders of voltages
phases that the density modulation of the stream
given the major ?elds are from the accelerator
is almost if not entirely lost.
grid [5 to the control grid. As is well known,
With arrangement of my invention, however,
the lines of force constituting such a ?eld ter 4.0
the space-charge region is so shallow that even
minate at right angles to the surfaces of the
the stragglers among the emitted electrons trav
?eld-de?ning electrodes. It follows that in the
erse it in less than a quarter cycle and instead
region adjacent the cathode the lines of force
of the density modulation of the electrons being
emerge from'the grid wires in the general di
lost they reach the anode in bursts of such power
rection of the cathode and then curve very "
and suddenness and with such close velocity
sharply toward the anode in a direction nearly at
grouping that I have termed cathode-grid com
right angles to their direction of emergence.
binations of this type “explosive.” The object of
There is also a fairly strong ?eld between the
the design is to make the electron reservoir con
control grid and the cathode‘ itself, which is
stituted by the space-charge region as shallow
superimposed locally upon the ?eld between the
as possible, and in practice the ideal can be so
control'grid and accelerator grid, and is direct
far realized as to permit density modulation of
ed toward, instead of away from the cathode.
electron streams at frequencies in the range of
As a result of the interaction of these two ?elds
1,500 megacycles, where in the past it has been
none of the lines of force from the accelerator
necessary to use velocity modulation, involving
grid normally terminate upon the surface of the
larger and more complicated structures, to get
cathode. .Emission has therefore no tendency to
reasonably e?ective results, even in smaller sizes
leave the‘ latter, since the space adjacent it‘ is
and at much lower powers than those here con
nearly’ neutral, with such Weak ?eld as exists
templated.
therein directed toward the cathode.
When the tube here shown is used as an oscil
60
As is the case with any grid-controlled tube
lator in the manner now to be described, the vari
operated through cut-off, when the grid swings
ous potentials are so arranged and proportioned
positivesome of the lines of force from the ac
that the transit time of the burst of electrons
celerator-grid which formerly terminated on the
is substantially one-half cycle; The anode I3 is
control grid now terminate on the cathode, and 65 in a tuned circuit, as is also the grid I6; The
condition of oscillation then is that the potentials
as the cycle progresses the cathode-control grid
of the anode and the grid swing in the same
?eld weakens or even reverses, permitting emis
sense, so that the grid reaches its peak of positive
sion toward the anode, and a space charge builds
potential at the same instant as does the anode.
up in the region immediately in'front of the oath
One of the results of the conformation of the
ode face which has the usual effect of limiting 70
electrostatic ?elds is a strong focusing action
emission. The distinguishing feature here is
upon the electron bursts, and these bursts ac
that the region where the ?eld is weak enough
‘ cordingly fall upon an extremely limited portion
to permit such space charge effect is very shal
of the anode surface, substantially none reach
low,so that even with the low ‘velocities imparted
to them by such relatively weak ?eld the elec 75 ing either of the intermediate grids. The anode
2,405,763
area upon which the electron bursts impinge is
that included in the V-shaped slot 20. The
reason for this arrangement is to spread the area
of impact and so increase the size and decrease
the intensity of maximum local heating, while
increasing the cross-sectional area of thermal
conductivity by ‘which cooling occurs, and also
to insure that secondary electrons are not pro
curately concentric with the remainder of. the
tube structure and, of course, to be vacuum tight.
At its upper end it is threaded to receive a grid
support ring 27, which is clamped between look
ing nuts 29 and 30, and an additional locking
screw M (Fig. 10) is also provided for further
security. The pairs of parallel grid wires l6
project from the ring 2? parallel to its radii, six
pairs vof grid wires being provided in the present
jected into regions of high ?eld intensity which
would accelerate them so that they, in turn, 10
design, the pairs being equidistantly spaced
would cause serious heatingaeifects.
around the periphery of the ring.
Two sliders are mounted on the column 25.
The
upper slider 28 comprises a short section of
oscillation, and it follows that immediately after
the electron burst has occurred the anode has 15 tubing 32 surfaced to a sliding ?t on the column
25 and shouldered at each end to receive discs
started to swing negative. The electrons accord
33 and 34 between which a short section of tubing
ingly reach their maximum velocity at or about
35 is clamped. The column 25 is provided in this
the plane of the accelerator grid--ideally, just
region with a longitudinal slot for the passage of
as they pass the effective plane of the boundary
a screw 37 which engages a piece of tubing 39
grid 4. As the anode continues to swing nega
tive they encounter a decelerating ?eld, either 20 sliding within the column. The tubing 39 termi
nates in an annular block All, and an adjusting
in an absolute sense or, if still being accelerated
rod 4! is threaded into one side of the block and
by the D.-C. ?eld, from the anode, at least in
passes to the exterior of the tube through a gland
comparison to the acceleration of the D.-C.‘
box 42 and a “Wilson seal” 43. It is apparent
?eld alone. In passing through this decelerat
that the position of the slider may be adjusted
ing field the electrons are delivering energy to
by sliding the rod 4|.
the anode circuit, and they are traveling at mini
A word as to the Wilson seal may here be in
mum relative velocity when they enter the slot
order, and in this connection attention is drawn
2B. This slot acts in some degree as a Faraday
to the showing at the lower right of Fig. .8. The
space, and the electrons suffer little change in
seal proper consists of a normally ?at washer 45
velocity or energy as they pass through it.
of synthetic or natural rubber, which is forced
Therefore their work is done and their transit
against a conical seat 4? by the internally coni
time effectively over assoon as they have en
cal edges of a gland 49. When the washer is un
tered it.
stressed the aperture therethrough is slightly too
Since the acceleration of the entire burst of
small for the rod 50 which it is desired to seal.
electrons takes place with substantial uniformity
The seal is lubricated with a small quantity of
they retain their close grouping .at the time of
vacuum stop-cock grease. Such a seal is vac—
impact, and since the impact occurs when the
uum tight under conditions where other known
electrons constituting the burst have suffered
types of packing would leak badly, Since the dif
maximum deceleration there is a minimum of
It has already been stated that the transit
time of the electron burst is one-half cycle of
energy wasted as heat and the oscillator conse
quently operates at relatively high efficiency.
For operation in the manner described the
desiderata are that the control grid t8 and ?la
ment ll should be effectively isolated from each
other both as regards D.-C. and radio-frequency
potentials, and should have an effective capacity
sufficiently low so that it may be tuned to the
desired operating frequency, or, in other terms,
it must be capable of being connected in circuit
with an inductance sufficiently small to tune to
that frequency. The accelerator grid It must
be insulated from the other elements to maintain
its D.-C'. voltage, but should be effectively
grounded as regards radio-frequency potentials.
‘The boundary grid 4 should also be grounded to
radio-frequency and for convenience in opera
tion and safety’s sake should preferably also be
ferential pressure on the washer serves to make
it hug the central rod more tightly and it _re
mains tight whether the rod be subjected to
rotary or sliding motion in either direction.
Returning to the general tube structure, the
second and lower slider Si is essentially similar
in construction to that just described, except that
its actuating rod .52 is mounted externally of the
column 25 through the gland box 42 and VWlsnn
seal 53.
The slider 5.! makes a close sliding ?t within
‘ a cylindrical conductor 54
mounted in the flange
it! accurately concentric with the column 25 and
maintained in this concentric relation both by
the slider 5| itself and by an auxiliary diaphragm
or spacer 55. The tubing 54 does not extend the
full length of the central column, but terminates
a distance above the flange 1 which is somewhere.
in the neighborhood of one-eighth of a wave
grounded as regards D.-C. potential, as it is elec
length at the mean frequency for which the tube
trically continuous with the envelope. The an
'
ode should be free as regards both A.—C. and ' (30> is designed.
D.-C. potentials.
Accurately coaxial with the column 25 and its
surrounding conductor 5! is a third conducting
The various mounting and auxiliary means
cylinder 51, mounted on the ?ange l and extend—
next to be described are designed to meet the
desiderata as fully as possible. In this descrip 65 ing below it for approximately one-eighth wave
tion terms such as “above” or “below” are used *
length, so that the two conductors 5d and'?'l over~
lap by a distance approximtaely equal to one
to indicate position as shown in Fig. 1. They
quarter wavelength of. the average operating fre
have no other signi?cance, as the device may be
operated in any position.
quency of the device, wavelengths in this sense
being used to .mean the wavelength of the fre
Starting at the bottom of Fig. 1, with the ?ange
iii, a ‘high conductivity column or pipe 25 extends ‘ 70 quency transmitted along the two tubes as a co
axial transmission line. There is no metallic con
a. major portion of the length of the entire device
tact between the two conductors 54 and 51, and
to the plane of the ?ange 3 and the boundary grid
they are separated by vacuum so that dielectric
4. This column is brazed or otherwise perma
loss does not occur in the space between them.
nently secured into the flange H1 so as to be ac- ,_
Column ‘5'! is brazed or otherwise secured in the
clothes
1i
?ange 1, is made of highly conducting material
(preferably oxygen-free copper) and is prefer
ably provided with a cooling system comprising a
water pipe 60 coiled around and soldered to the
external surface of the column. The ends of this
pipe are brought out through the ?ange ‘I at the
12
is 50 mils. The grinding is preferably performed
in a jig which deforms thewire slightly in the
longitudinal direction, so that the ends of the
?lament are ground a few thousandths of an inch
thinner than is the central portion.‘ This grind
ing forms the flat emitting surface of thev?la
ment, and if done with a relatively small wheel
whose axis is maintained parallel to the length
of the ?lament, it gives the slight hollow grinding
which has already been stated to be advantageous.
The effect of thinning the two ends, adjacent the
point where the ?lament is clamped, is to give a
greater current density at these points, with a
consequent greater liberation of heat which com
pensates for the heat conduction to the clamping
means and results in substantially constant tem
perature and substantially constant emission over
the entire effective length of the ?lament. Being
right of Fig. l.
The upper end of the column 51 carries an in
termediate ring (H which supports indirectly one
end of each of the ?laments H’. The other ends
of these ?laments are carried by a group (here
six) of pipes 62 mounted in the annular inter
space between the column 51 and the outer shell
5. The lower ends of the pipes 62 are mounted in
a ring 63 which is bolted to and insulated from the
?ange ‘I as is shown in Figs. 2 and '7. The ring 63
is 'counterbored at three equidistant points to re~
ceive insulating beads 64 of porcelain, lava, or
of pure tungsten, the ?lament retains a degree of
resiliency even at its emitting temperature, and
space the rings slightly from the ?ange ‘I. A cap 20 this, together with tis resilient support, prevents
screw 85 passes in turn through a clamping cap
buckling or change of plane of the emitting sur
61, a second bead 69, the ring 63 and the bead 65
face when in operation and keeps the electrical
to clamp the ring ?rmly to the flange. It should
constants of the device ?xed under such minor
be noted that the potentials which this arrange
variations in operating temperature and expan
ment must withstand are of low frequency and 25 sion, and inequality in these factors as between
are only those across the ?lament, i. e., the in
the several ?laments, as inevitably occur in prac
sulation need only be of su?lcient value to with
tice.
stand a few volts (three at 60 cycles in the instant
Cooling for the support of the inner ends of
structure) and the insulating material is not
the ?laments is accomplished by conduction
subject to dielectric heating from radio-frequency 30 through the support rings ‘l4 and 6! to the col
umn 5i and thence through the cooling coil 60.
?elds.
' The actual ?lament mounting can best be seen
Cooling for the outer supports is by circulatory
in Figs. 11 and 12. Each of the tubes 53 carries
systems within the support pipes 62 themselves.
an inwardly projecting L-shaped lug l0, and the
A small water pipe 98 enters the side of each of
35
inner ends of the lugs are provided with slots 7!
the support pipes 62, and extends axially within
for receiving the downturned ends of the staple
it to a point adjacent the lug "iii, so that water
other refractory insulating material which beads
shaped ?laments H, the ends being clamped into
entering this pipe will be squirted against the
place by set-screws 12. The inner ends of the
inner end of the lug. From there it returns
?laments are clamped in an annular groove 13,
through the pipe 62 externally of the pipe 90 to
formed in an inner mounting ring ‘I4 which is 40 the bottom of pipe 52, where the end 90’ of the
supported on column 51 by the intermediate ring
next pipe is comiected to carry the water to the
6i before mentioned. The actual clamping of
next ?lament support, circulation thereby occur
the ?lament ends is accomplished by pairs of set
ring through each of the support pipes 62 in suc
screws 15 bearing on small blocks 11.
The pipes 62 are surrounded by open-ended 45 cession.
The supply for this circulatory system is
cylindrical conductors 19, which terminate at the
through a ?tting designated by the general ref
level of the upperend of thelug and extend down
erence character 9i, comprising coaxial pipes
over the pipe ‘52 for approximately one-quarter
92 and 93 which connect respectively to the two
wavelength and are supported by the ring 6i.
ends of the system. The outer of these pipes is
Within the conductors ‘I9 are inner tubular con O permanently secured to the support ring 63 (see
ductors 80 of substantially the same length, open
Fig. 4) . The ?tting 9i passes through the flange
at their upper ends and mounted by their lower
'1 and is insulated therefrom by insulating bush
ends on the pipes 62 by means of conductive
ings 94 of steatite or other refractory between
‘blocks 8|. The concentric tubes 19 and 80 are
which is a compressed rubber washer 95 forming
both open at the ?lament end, being notched to
a vacuum-tight seal. A connecting lug 91 for
clear the lugs 16 and also being provided with
connecting one ?lament supply lead is mounted
‘ alined holes to permit tightening of the set-screws
upon the ?tting 9i, and the ring 33, and the cir
‘12. It will thus be seen that the only connection
culatory system comprising pipes 89 and 62 all
between the inner column 51 with its supporting
constitute the conducting system for supplying
rings El and ‘i4 and the group of ?lament sup 60 the ?lament current. The return circuit is
port tubes 62 is the ?laments themselves.
through the column El and the ?ange ‘I, to which
These are shown in Fig. 17, and as will be seen
asecond connecting lug (not shown) is attached.
are relatively short and rigid. They are prefer
There are two other features comprised within
ably of pure tungsten and have a considerable
the ?lament-grid structure and their supporting
degree of strength. It will further be seen that 65 systems. The ?rst of these is a sliding plug 99'
the support afforded their outer ends by the tubes
mounted in the end of the inner support column
'62 and lugs 10 is light and of small inertia and
25; and adjustable as to position by means of
that the tubes 62 have relatively large resiliency.
an operating rod 150, and an offset extension
The ?laments therefore are very unlikely to be
rod l0! passing through a Wilson seal H12 in
ruptured by shock on the device as a whole, and 70 the gland box ‘32. The second is a cooling pipe
there is ample ?exibility to take up their expan
I03 which extends substantially the full length
_ sion.
of the inner column 25 and is soldered thereto
Each ?lament is preferably. formed of round
adjacent its upper end for better heat transfer.
tungsten wire, one surface of which is ground
We are now in a position to consider the elec
l
?ator slightly concave. The diameter here used is
£2,405,763
.
.
14
l3
trical characteristics of the ?lament-grid struc
the tube of my invention may be considered from
ture in view of the desiderata above set forth,
a number of aspects, all depending on the gen
and it is vbelieved appropriate to do this at this
eral relationships above set forth, but in the
point, since the same principles are involved in
treatment here adopted they are generally con
the supports for the remaining elements of the 13K sidered as divided into sections of quarter-wave
device and the explanation of all will be sim
length, or thereabout, as this is believed to lead
pli?ed if these principles are in mind. The nec
to the simplest explanations.
.
essary separation of the elements as regards
We are interested in the impedance of the grid
D.-C. or low frequency potentials have already
filament support line as viewed from the grid
been accounted for. There is no metallic con 10 end, but this impedance is dependent upon the
nection between the grid-support column 25 and
terminating or output impedances of the various
the ?lament-support system comprising the col
umn 57, and the support pipes 62. Remaining
to be accounted for is the impedance relationship
between the grid and ?lament members, and
sections, and therefore, in order to determine
what the grid-end impedance will be, we must
consider the various elements, section by section,
starting from the outermost or lower end of the
tube as shown in Fig. 1.
From this aspect the ?rst section of the struc
this is dependent upon the impedance of the
coaxial transmission line formed by the inner
and outer columns 25 and 51 and the coaxial con
ductors associated therewith.
The impedance characteristics of transmission ,
lines whose lengths are of the same order of
magnitude as the wavelengths of electrical oscil
lations transmitted thereby are now well known,
but they are restated here for convenience in
the explanations that follow. Most of them can
be derived from the impedance diagram of a
half-wave line open at theoutput end, as shown
in Fig. 32, which indicates such a line diagram
tubular conductor 54 illustrated as below the end
of the column 51. Electrically this portion of the
structure is a single conductor, and viewed‘ from
its upper end constitutes an end-fed antenna. It
is preferable that its length be of the order of
one-half wavelength at the operating frequency
of the device, in which case its effectiveimped
ance Z2 will be in the neighborhood‘ of 1,000 ohms.
If its length be reduced to one-quarter wave
matically, and shows'the approximate curve of
relative impedance looking into any portion of _
the line from the right, resistance of the con
ductors themselves being assumed to approach
zero.
ture is the section including the adjusting rods
52, M, etc., the ?ange I U, and the section of the
length its effective input impedance‘ will likewise
be reduced to the neighborhood of from 50 to 100
ohms, the quarter wavelength condition being
the least desirable in practice. This antenna is
considered as being fed by the coaxial transmis
sion line comprising the tubular conductor 54
as the inner element and the column 51 as the
outer element. With the spacing shown such a
Extremely short sections show a high
capacitive reactance, which falls to the charac
teristic impedance of
V?
transmission line will have a characteristic or
surge impedance Z0 of about 10 ohms, and as has
already been stated the length of this section
of the line at the 1/8 wavelength point, and to
zero at the quarter-wave point, i. e., a quarter
wave open-ended line acts as a dead short. From
40
of transmission line is approximately M4, where
k is the wavelength at the frequency of operation.
If we consider the quarter-wave condition to be
this point on the'apparent reactance is induc
tive, rising again to the value
ful?lled exactly the impedance looking into the
45
O
at the 3/8A point and approaching in?nity at
coaxial line from the grid end will be
Z2
1/27\.
.
.
If the antenna section of the system have an
The same diagram may be taken as represent
impedance of the order of 1,000 ohms, the char
ing the impedance of a shorted~end line if the ori 50 acteristic impedance of the line being 10 ohms,
gin be taken at the nodal or quarter-wave point,
the input impedance of the line will therefore be
which appears as a short when looking into the
116 of anohm. This low impedance therefore be
line. For short sections the reactance is small
comes the closing impedance of the section of line
and‘ inductive, it rises to
immediately preceding it. From one point of view
55 it acts as a radio-frequency by-pass between the
inner conductor 54 and the outer conductor 51, so
v?
that viewed from the input end, at radio-fre
quencies the cylinder 54 and outer column 51
at the IASX point and approaches in?nity at M4.
Since this appears as an open circuit, increasing
appear as a single conductor, and form, in con
the length of the line repeats the portion ofthe 60 nection
with inner column 25, a single radio-fre
diagram shown at the left of the nodal point.
quency transmission line considered as fed from
Stated in another manner, a quarter-wave open
the grid-?lament end through a slight imped
ance irregularity where the inner cylinder 54
terminates. Its effect from another point of view
will be considered later.
I line or a half-wave shorted line appears much
like a series resonant circuit, while a quarter
wave shorted line or a half-wave open line ap
pears like an anti-resonant or parallel resonant
Even if the conditions as to impedance of an
circuit.
tenna and length of the coaxial line constituting
’ The only other relationship necessary to the
understanding of the present invention is that
the characteristic impedance of a quarter-wave
line‘ is the geometric mean between its input and
closing impedances. The short-circuit and open
circuit conditions are, of course, merely special
‘cases of this general relation.
The lines comprising the element supports of
70
A75
the column 51. and cylinder 54 are not exactly
met the result will be substantially the same.
The antenna impedance can easily be kept above
100 ohms, making the impedance looking into
the quarter wavelength line 1 ohm. If the length
of the line section is not exactly one-quarter
wave, but is still materially greater than one
eighth wavelength, the input impedance will still
2,405,763
15
introduce large losses through radiation and di
be low in comparison with the characteristic im
pedance of the line, and although more power will
electric phenomena. ‘
The design problem to be met, therefore, is the
design of a structure which, when terminated by
an impedance approaching in?nity, will have the
properties of an anti-resonant circuit as viewed
from cathode and grid. This structure is provided
by two additional quarter-wave sections of the
escape than if optimum conditions are met the
amount of power wasted by such undesired radi
ation will be very small.
The section of the inner line comprising the
cylinder 54 and column 25 terminates in the slider
5|, which, as it is of large area and makes good
contact with both conductors, vmay be considered
as of zero impedance. This section may be tuned
to exactly one-quarter wave by moving the slider.
Due to the spacing between the two conductors
the characteristic impedance of this section of
transmission line is high, and if the resistance of
same line.
‘
The ?rst of these sections extends to include the
upper slider 28, and its design is such that its
electrical length may be changed in opposite sense
to its physical length; i. e., such that it may be
“?tted in” beneath the section above it even
the line were zero the input impedance would be 15 when the length of the upper section increases
with decreased frequency of operation or vice
in?nite. Actually it may always be made to ex
ceed 100,000 ohms and under optimum conditions
may reach ten times this value. This section
versa.
.
extremely high impedance interposed between
This eifect is obtained by means of the irregu
larity introduced by the low-impedance line sec
tion constituted by the slider 28. From the top
the ?lament-grid structure and the outside world,
and the impedance involved is so high that prac
tically all energy reaching it is re?ected back to
to the slider is a length of relatively high im
pedance line of less than 1/; wavelength which
therefore forms a tuned radio-frequency choke of
its source.
'
of the high impedance section already described
therefore appears as a capacity variable from
zero to some small value as the slider is moved
‘
What actually happens can be expressed more
nearly in the terms of low frequency power line
transmission if we think of the antenna as a
load which is fed by a lineterminating immedi
ately abovethe top of the column 54. Current
fed to this line from the central column 25 must
proceed down the column, across the slider, and
back to the top of the conductor 54, since owing
tov skin e?ect none will flow transversely through
the wall of the conductor. In so flowing the cur
rent meets an enormous impedance-say 100,000
ohms. From there the line continues down the
outside of conductor 54 to the antenna and back
within the column 51 to the terminus above the
to change its length from zero toward M4. To
this is connected the relatively great capacity of
the slider portion of ‘the line about l/gx in length,
but presenting an effective capacity many times
as great as and apparently in parallel with that
of the lower section, so that moving the slider to
change the length of the section below it changes
the apparent capacity as viewed from above rela
tively little. Therefore a very short length of the
35 high impedance line above the slider is all that is
necessary to tune this effective capacity to reso
nance, thus completing the quarter-wave section
of line and bringing the node or quarter-wave
point of the composite section a small distance
top of conductor 54. This latter length of line,
including the load imposed by the antenna, has 40 above the upper slider face. The distance be
tween the slider and the node will vary with fre
an impedance of, say, 1 ohm, and since the voltage
quency, of course, but only slightly with the posi
available at the termini of the line will divide
tion of the slider.
itself across this low impedance and the high im
pedance line section in series therewith in the
proportions of the magnitudes of those imped- ,
ances, and since the current ?owing at the input
points of the respective sections is the same, it'
follows that the energy delivered to the respective
impedances will also be in proportion to their
magnitudes, and only 1/100,000 of that delivered to to
the line will be transmitted to the antenna to
be radiated thereby--still less if optimum condi
t has already been pointed out that the node
is eifectively equivalent to a short-circuit, and
hence, since by moving the slider we may move
the position of the node, by so doing we may tune
the uppermost section of the line including the
?lament and grid. We have made that portion
of the line below the slider and above the im
pedance loop relatively ine?ective in tuning, so
that we have an “elastic” or extensible quarter
wave section of line.
The ?nal or grid-?lament section may thus be
From still a slightly diiferent aspect, the small
resonated
or otherwise tuned to give optimum op
55
and largely resistive impedance o?ered by the
erating conditions. In the case of Fig. 1, where
outer line is at a current node. We therefore
capacity feed-back between anode l3 and grid
have a very small current flowing, and therefore
cap
99‘ is used, the desired tuning of this section
the value of PR is vanishingly small, the R in
must provide a capacitive reactance. This is ob
this case being the apparent input impedance of
the outer line and 12B. (practically) the energy 60 tained by making the grid-?lament section slight
ly longer than one-half wavelength or, in other
radiated.‘
terms, tuning it to a slightly lower frequency than
From whatever aspect the matter be considered
that of the desired oscillation, so that as viewed at
the result is the same: The sections of the trans
grid and ?lament it presents a small anti-reso
mission line above the current node terminate
nant capacitive reactance. Under these circum
in what is equivalent to an open circuit, just as
stances the ?lament-grid system appears as a
would" a low frequency line connected acrossan
capacity in series with the capacity between ‘the
ordinarily good insulator. There is some con
grid structure and the anode, and this latter
sumption of power, which can be neglected in
capacity is adjustable by varying the position of
further consideration, (as in the case of the in
sulator) and the succeeding sections can be 70 the cap 99. When, therefore, the potential of the
anode swings, the grid will assume a potential
treated as if they terminated at ‘this point in an
tions are met.
in?nite impedance. It should be noted, however,
that at the frequencies we are considering sub
stitution of an insulator for the line sections
with respect to the ?lament (and ground)
which is intermediate between cathode and an
‘ode potential, and which bears the proportion to
.would drop the impedance‘ to a‘?nite value and 76 the total potential between anode and ?lament
17
2,405,763
that the e?ective series capacity between anode
grid and grid-?lament .bears to the apparent ca
pacity between ?lament and grid. In other
words, the arrangement is essentially a capacitive
voltage divider which swings the grid potential
in the same sense that the anode potential swings,
and in ?xed and predeterminedproportion there
to. Since the criterion for oscillation of the ‘de
vice is that the grid and anode should swing in
18
?ange '3. This side tube carries at its outer end
a .?ange 10‘! which is surfaced to receive the tu
bular glass insulator I09, and the latter, in turn,
carries a terminal ?ange H0. This structure
may best-be seen in the enlarged detail View of
Fig. 6. As in the case of the ‘main tube envelope,
‘the tie-bolts which hold the structure together
are omitted, but it will be understood that it is
‘the same sense and in step, the result is a highly 10 assembled in the same fashion as is the :main
envelope with ground surfaces reenforced by
e?'ective capacity feed-back which is under con
greased rubber bands or gaskets III which form
trol either by varying the actual capacity cou
the seals. Two tubular conductors are ?xed to
pling with the cap 99 or by varying the effective
resonant input capacity of the grid-?lament cir
cuit by varying the position of the slider 23,.
By the use of the two sliders the device ‘is thus
given ‘its very considerable tuning range. The
lower slider 5| brings the current node to the
point where the antenna is fed; the upper slider
28 moves the nodal point immediately above it ‘
and thus tunes the ?lament-grid section. The
actual point of importance ‘is that by adjusting
the position of the sliders the e?ective resonant
impedance of the ?lament-grid combination may
be made to assume any value which may be de- ~»
sired, since the node above the slider 28 may be
moved near enough to the rather large lumped
cathodeegrid capacity to embrace between the
and project inwardly from ?ange H0. The inner
conductor I I2 is spaced from the outer conductor
H3 and is held accurately concentric therewith
by .an annular spacer H4. The accelerator grid
I5 is supported from the inner member by a
tubular bracket M5, the end of which ?ts within
the conductor .1 t2 and is rigidly secured thereto.
A cooling pipe H1, bent into a ring to surround
the accelerator grid, has its ends brought down
parallel to the support bracket H5 and enters
the inner conductor on either side thereof, the
ends .of the pipe ‘passing into the inter-conductor
space distally of the spacer H4 and emerging
through the flange IN).
A tuning slider H9,
which nearly ?lls the space ‘between the inner
and outer conductors and does not make factual
‘node and that capacity the exact small line in
vductance .required for tuning it. ‘In actual prac 3-0 contact therebetween, is operated by means of
a hook 529 whose end projects through a lon
tice the effective impedance will be made capaci
gitudinal slot in the conductor H2. A control
‘tive and small "in comparison with the physical
rod I2! ‘is threaded to the end of the hook and
grid-cathode capacity, but it might, if desired,
emerges through a Wilson seal 122.
equally well be made inductive or resistive. Fur
‘The supporting bracket H5 and cooling tubes
thermore, since the effective resistances in the
H‘! are carried up to the :interspace between the
circuit are extremely low, and the losses are .also
control grid and the boundary grid through an
small even though the circulating currents ‘may
angular ?tting or shield I25, which passes
be large.
A system .of transmission lines, chokes and by
through a notch i 2'! cut in one side of the ?lament
passes similar to that used in the ?lament-grid 40 support ring 6|. This -'construction is shown in
Figs. 1, 6 and 11,, each of these ?gures showing
circuit is .employed across the ?lament to pre~
sections of the shield. The shield is electrically
vent transmission of energy to D.-C. insulation
continuous with a pan I29 overlying and contact
and to prevent ?lacnent damage by R. F. cur
ing
the ?lament support ring 14 and slotted im
rents. The actual ground point on the ?lament
above the ?laments, which forms an
circuit is the ?ange 1 on the outer casing .5 of it mediately
additional shield or barrier to separate com
the device. This, however, is unimportant and
pletely the anode and control-grid sections of
the effect of the transmission line arrangement
the tube except at the points where intercom
may be considered as though the ground point
munication is necessary or desired. The shield
were at ‘the inner end of the ?lament. This may
and pan therefore form one terminus, and the
be considered as terminus of a quarter wave .50
accelerator grid and cooling pipe H1 ‘form the
length coaxial transmission :line comprising :the
tubular conductors ‘i9 :and 36, ‘which ‘is open at
its lower end, terminating in a high impedance.
other terminus of the radio-frequency transmis
sion line ‘comprising the side ‘tube i135 and the
tubular conductors H 2 y and l ‘I 3.
The transmission line impedance is again low,
From ‘what has gone before it :is believed that
being of the :order of, say. '5 ohms, and the line 1;
the operation of this arrangement will be readily
therefore :forms a negligible series impedance as
apparent. Again we have an antenna system
before, acting as a by-pass ‘to the inner conduc
comprising
the control rods I21 and cooling tubes
tor. This, again, is a quarter wavelength line
H'l, plus the projecting end of the conductor ‘H3,
with the pipe 62 as its inner conductor, terminat
which is fed, by and offers a relatively high im
ing in a dead short, and therefore o?ering very .00 pedance to a quarter wavelength transmission
high impedance. As the potential imposed :across
line of low impedance formed by the side tube
this impedance is merely that which can ‘build
I05 and the conductor H3, and there vis accord
up across the short ?lament, amounting to a few
ingly a radio-frequency ‘by-pass between the
volts at most, the escape of power through the
grounded outer case ‘5 and tube Hi5 of the con
?lament support may be neglected, and :the vhigh "
ductor H 3. Within this there is another series
impedance e?ectively in series with the ?lament
section .of transmission line comp-rising the con
prevents circulation of IMF. currents which might
duc'tors H2 and H3 and terminating in a short,
otherwise cause hot spots and burn-outs.
formed by the spacer H4. This inner ‘line is
We are now ready to consider the mounting of
tuned to a quarter wavelength by means of the
the remaining elements, '1. e., the accelerator grid,
slider In, which acts as a loading capacity and
boundary grid, and anode, which velement-s are
increases greatly the electrical length of the line.
shown in elevation in Figs. ‘9, 15 and 13 respec
tively. The accelerator grid is mounted .from ‘a
side tube 105, which is welded to project through
the wall :oft-he housing 5 immediately below the
In {practice this slider is moved back to a point
from which the line appears as a very large ‘in
ductance ‘at the operating wavelength.
The
proper point is that at which the remaining-in
2,405,763
20
ductance and capacitance of the line, considered
from the grid end, makes it just a quarter wave
length from the inner end to the shorting spacer
I I4, forming a very high impedance at the shield
where the grid I5 and cooling tube III are sup
ported, and preventing any appreciable power
being transmitted past this point to be radiated.
The capacity of the grid I5 to the boundary grid
4 is large, and that to the control grid I6 is small;
there is little coupling tending to swing the ac
celerator grid I5, and it consequently tends to
maintain very nearly zero R.-F. potential.
As has already been described and as shown in
detail in Fig. 16 the boundary grid 4 is ?rmly
clamped between the ?ange 3 and the anode
housing, 2, and is therefore physically and de?
nitely at the ground potential of the housing.
The boundary grid and the anode face I3 again
form the termini of a resonant line, comprising
1
The supporting pipe I44 enters the ?ared cyl
inder I4'I through an aperture in the side thereof.
The end of the pipe is threaded into a boss I48
on an inner ba?ie cylinder I50, which boss is
soldered to the inner wall of the cylinder I41.
The boss I48 extends internally to form a cylin
drical chamber I5 I, which connects by a side pipe
I52 through the end I53 of the baffle cylinder, so
that water introduced through the pipe I44 is
discharged directly against the active face I3 of
the anode, and thence is forced around the exte
rior of the baille cylinder to reenter its open end.
It can then return within the cylinder to enter
the open end of a return pipe I54, which is mount
ed concentrically within the pipe I44 by means of
a perforated cap I55 which fits over the end of
the pipe I44, its lower end passing out through
the discharge chamber I5I. The cap compresses
a rubber gasket I46, sealing the joint between the
pipe I44 and the anode body to make it Water and
the housing 2 as its outer conductor and a cylin 20
vacuum tight.
drical anode body, designated by the general ref The upper end of the pipe I54 is centered in
erence character I30, within the housing, This
the pipe I44 by means of a metal bellows I5'I
resonant line is one-half wavelength long, and
may be considered as terminating between the
inner face of the ?ange I and the end I3I of the
anode body. This will be recognized as an open
ended half wave line, and therefore of extremely
high impedance when viewed from either end.
The construction' and method of support of the
anode body are best shown in Fig. 8. The support
is from the mid- or quarter wavelength point of
the anode, i. e., at a potential node, so that there
is little tendency for power to escape from the
support structure. Such tendency as there is for.
which is sealed to both pipes and permits differ
ential expansion between the two. Water is in
troduced into the pipe I44 through a side pipe I59,
and its course can be traced by the arrows in the
drawings through the outer pipe, the perforations
in the cap I55, the side pipe I52, and thence
around the ba?le cylinder I50 and back through
V the central pipe I54.
The action of the mounting follows the princi
ples already set forth, although the application
is somewhat different. A disc I60 is connected to
35 the ?ange I4I both electrically and mechanically,
and carries a cylinder IBI. The pipe I44 and the
pressed by either or both of two methods. First, ‘ cylinders I40 and IBI form a transmission line
power to leak from the support point is sup
and preferable in the cases where the tube may
be predesigned to operate at a ?xed wavelength, is
one full wavelength long. Electrically this might
equally well be a half wavelength line, but ad
' a movable plate I32 mounted on the sliding rod
ditional space is needed for the iinsulating cyl
50 of the'Wilson seal ?rst described, and making 40 inder I42, which must withstand the full D.-C.
contact with the ?ange I by means of a spring
anode potential of 20,000 volts or more. The
skirt I33. This may be adjusted to bring the node
length of this section is measured from the anode
of the resonant line accurately at the point of
and its housing, and the impedance at its outer
support. This method of preventing direct radia
end is very high, so that looking into it from the
tion from the anode was adopted in the ?rst of 45 anode the impedance is also very high.
these devices constructed. It was quickly found,
This high impedance is connected in shunt
however, that the plate I32 Was more useful as a
across the line formed by the anode body I30 and
tuning device, and therefore the principle of
anode housing 2 very near the nodal point, where
transmission-line-choke support was again em
the
impedance of the latter line is low, and ac
50
ployed to prevent power escape. In the construc
cordingly a very small portion of the current
tion then adopted and here shown a side tube I40
of relatively large diameter is welded at substan-v
tially the midpoint of the anode housing 2. The
?owing at this point will take the high imped
ance path to the outer world.
In other terms, the full wave line is connected
side tube carries a metallic ?ange I4 I, with a glass
insulator tube I42 ?tted against it and in turn 55 so near the node of the main anode oscillator cir
cuit that only a few volts are effective across its
carrying a terminal ?ange I43_ Through this
termini,
and therefore very small currents will
terminal ?ange passes a pipe I44 which projects
tend to flow therein, representing a power loss of
through a pass hole I45 in the side of the anode
VZ/Z where V is the small input voltage and Z
housing and on the end of which the anode body
is attached. The action here will be described 60 the large input impedance. Moreover, since the
line is one wavelength long, only the small voltage
following the mechanical description of the
V will be effective to cause radiation from the
anode, as the expedients adopted are predicated
radiating system constituted by the end of the
upon the necessities of the mechanical structure.
line. It should be noted, however, that by de
From the electrical point of View the anode
body is a simple cylinder with closed ends. Its 65 liberately unbalancing the anode resonator by
means of the plate I32 the support system can
complexity, as shown in Fig. 8, is due primarily
be converted to a horn antenna which can be
to the provision of circulating cooling water with
made to radiate as much high-frequency energy
in it, and to the provision of what may be termed
as the device will produce.
a “rough tuning” device.
Owing to the necessity for providing cooling the 70
. body itself must be water-tight, and accordingly
it is constructed of a ?ared cylinder I41, to the
?ared end of which the anode face I3 is hard
It will be noted that the arrangement described
leads to and permits a new type of cavity reso
nator; i. e., one wherein various portions may be
operated at di?erent D.-C. potentials, so that
D.-C. accelerations can occur while electrons are
soldered. The other end of the cylinder is closed
75 within the resonant cavity. Such acceleration is
by a threaded disc I49.
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