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Патент USA US3041514

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June 26, 1962
M. B. KNIGHT ErAL
GRID MOUNTS Foa ELECTRON TUBES
Filed Sept. 1, 1959
3,041,495
United States Patent O rice
3,041,495
Patented June 26, 1962
1
2
3,041,495
the frequencies of these two resonances typically differ
by less than 5 percent.
It is therefore an object of this invention to provide a
new and improved grid structure that is substantially free
GRE MÜUN’I‘S FÜR ELECTRON TUBES
Mark Berwyn Knight, West Caldwell, NJ., and John
Joseph Thompson, Brooklyn, N.Y., assignors to Radio
Corporation of America, a corporation of Delaware
Filed Sept. 1, 1959, Ser. No. 837,449
12 Claims. (Cl. 313-350)
This invention relates to grid mounts for electron tubes.
In particular, this inventionrelates to 'grid mounts hav
ing grids that are of the multiple-siderod, cylindrical type
and which are supported at one end only.
IThe grids used in certain types of tubes, such as some
receiving tubes and some power tubes are of a cylindrical
shape and comprise a helix of fine wire brazed to a plural 15
of microphonics.
It is another object of this invention to provide a novel
tube including an improved grid structure of the canti
lever supported type which minimizes mechanical vibra
tions of the grid while not substantially effecting the elec
trical parameters of the tube.
These and other objects are accomplished in accord
ance with this invention by providing a multiple-siderod,
cylindrical grid of the cantilever-supported type with one
or more coarse-pitch helices of line wire which may be
considered as truss wires, mounted on the same grid
supports with the conventional fine-pitch helix which is
used for electron control. This small additional wire,
with proper geometry, not only damps the vibrations
more quickly, but stilfens the grid and thereby increases
are supported ñrmly at one end and usually are free at
the other end for electrical purposes and for ease of 20 the resonant frequency of the grid substantially without
significant change in the electrical characteristics of the
manufacture. '
tube.
The response of cantilever-supported electrode struc
The invention will -be more clearly understood when
tures to mechanical vibration is entirely different from
read in conjunction with the accompanying single sheet
that of the electrodes in conventional receiving tubes.
The conventional electrodes, which are supported be 25 of drawings wherein:
IFIG. l is a top partially schematic view of a grid
tween mica spacers, must be provided with a sliding lit
while under the harmful mode of mechanical vibration;
in the spacers to allow for differential thermal expansion
FIG. 2 is a side view of an improved grid in accord~
of the several electrodes. The tolerances associated with
ity of supporting siderods of heavier wire. The siderods
usually number eight or more while the helix usually is
made with several hundred turns per inch. These grids
these fits permit more or less “rattling” in response to
ance with this invention;
mechanical vibrations. The “rattling” modifies greatly 30 FIG. 3 is a side view of anY embodiment of an improved
grid in accordance with this invention;
the frequency characteristics of the mechanical excitation,
FIG. 4 isa side View of an improved grid in accord
and provides high-frequency excitation to the electrodes
ance with my invention;
even though the tube envelope may not experience these
FIG. 5 is a side view of still another improved grid in
frequencies. Also, the rattling tends to damp natural
35 accordance with my invention; and
vibration frequencies of the whole electrode.
FIG. 6 is a sectional view of a receiving type tube
The cantilever structure, by contrast, is effectively one
utilizing this invention.
piece and allows virtually no relative displacements of
One speciñc grid design of the type under consideration
electrodes except near the mechanical resonant fre
herein, and illustrated in FIG. l, uses as the control vgrid
quencies of those electrodes. The resonances of the elec
trodes are not excited unless the applied mechanical mo 40 wire, a helix 12 of 320 turns per inch of 0.8 mil molyb
denum wire or one of 400 turns per inch of 0.5 mil molyb
tion contains components at or near the resonant fre
denum wire. Mechanical support of the helix 12, as well
quencies. In further contrast to conventional structures,
as the electrical and the thermal conduction paths are
the vibrations in the cantilever structures are damped only
provided by twelve siderods 14, arranged parallel to the
by the losses involved in straining the materials. Still fur
ther, the resonant frequencies of cantilever elements are 45 axis of the cylinder, of 1.5 mil molybdenum wire brazed
on the outside of the helix. This cylindrical grid is
lower than those for similar elements supported at both
ends.
Some mechanical resonances in this type of structure
tend to produce relatively large, undesired electrical out
puts (microphonism) when mechanical vibrations of that
frequency reach the tubes. In order to reduce undesired
microphonic'elfects, it is desirable to have the mechanical
resonant frequency as high as possible, because the ampli
tude of vibration tends to be lower and because high
brazed to a flange (not shown) supported by three legs
from a ceramic base wafer in one known tube type. The
' inside diameter of the cylinder is .066 inch and the free
length above the ilange is .235 inch.
j When gridsV of the type brieily described above, and
without -benefit of the present invention, are subjected
to a mechanical impulse, e.g., a sharp tap, a train of
damped oscillations occurs. The wave-form of the oscil
mechanical frequencies are usually transmitted to the 55 lations produced is complex during the first one to five
milliseconds after the impulse, indicating a mixture of
tube ineñiciently. Furthermore, as the mechanical reso
several frequencies. Then, there is a relatively slow
nant frequency is increased, the vibrations tend to decay
decaying oscillation at about 3000 cycles for the 0.5 mil
more quickly. In other words, high-frequency mechani
wire grid and about 5000 cycles for the 0.8 mil Wire grid.
cal vibrations are less common, and are less harmful, than
60 This damped oscillation characteristically appears to be
low-frequency vibrations.
amplitude modulated to 50 to 300 cycles. The amplitude
The various vibrational modes of cantilever supported
decays exponentially to 37% of the original after 500 to
grids have been studied. One mode of vibration has
1000 cycles of oscillation.
been found to be especially serious in producing spurious
When the tube is mechanically excited, e.g. with a
electrical output signals from the tube. In this mode, 65 loudspeaker and audio oscillator, it is found that the
the grid sways as a column, from its supported end. This
grid vibrations actually consist of two sharp resonant
sway could occur in any direction, -but it has been found
frequencies separated by only 50 to 300 cycles. The
that inadvertent dissymetrics in the construction of practi
presence `of the two frequencies makes it obvious why
cal grids yield preferential directions of sway. Two reso
the damped oscillations, described above, have the appear
nances'of this mode have been observed, with the di 70 ance of amplitude modulation, i.e., the amplitude changes
rection of motions of these two resonances at right angles
to one another. In the type of grids under consideration,
are like “beats” between the :two frequencies. These
two frequencies represent the two directions of sway men
3,041,495
tioned previously. Other smaller resonances can often be
' malte _the truss wire diameter larger than the helix wire.
found at higher frequencies but these smaller high fre
quency resonances do Vnot normally produce seriously
objectionable microphonics, asv would -be expected from
the results of the impulse test.
f
e
When the truss wire is considerably smaller than the helix
wire, however it is not strong enough for the relatively
large mass of the grid.
'
'
Several modesof vibration have been observed. With
the'speciiic grid design described above, the sway mode
vibrations, as shown in FIG. 1 (the displacement of ¿the
grid being indicated by the dotted lines), are at the lowest
frequency and are of the largest amplitude among lthe 10
modes observed. Also, the sway mode has been found
to be the only mode which substantially añects the elec
trical characteristics of the tube. In the sway mode, two
Relative
.
Resonant
Helix Wire
Truss Wire
.
,
Stitiness
Frequency, With Truss
c.p.s.
Compared
To No
Truss
none ________________ -_
7 t.p.i., 0.5 ruil--
3,200
4, 300
1.0
1. 8
l2 t.p.i., 0.5 mil.
4, 500
2.0
resonances Vhave been observed V(only one of which is
12 t.p.i., 0.8 mil _____ __
2-7 t.p.i., 0.5 mil ____ _-
4. 600
6, 000
2.1
3. 5
shown) 4.which represents motion in two directions, 9'()
2-14 t.p.i., 0 5 mil
3-6 t.p.i., 0 5 m
6, 400
8, 1.00
4. 0
6. 4
__
-_
none _____ __’___
12 t.p.i., 0.8 mil _____ __
3-6 t.p.i., 0.5 mil ____ __
4, 800
6,300
7, 500
1. 0
1. 7
2. 4
D0 _____________ _-
3-6 t.p.i., 0.8 mil ____ __
9, 800
4. 2
degrees with respect to one another. The amount of
frequency separation of the two sway mode resonances is
an indication of the degrees of symmetry of the structure.
In tubes using an 0.8 mil grid helix i12, the average of
the two sway mode resonances is about 4800 cycles.
When the grid is under vibration in the sway mode, as
shown in FIG. 1, the substantial rectangles normally
«formed -by the siderods 1‘4 and helix wire 12 are dis
torted. Since the helix wire and siderods are brazed at
the joints, the helix wire must bend, Therefore, Vthe
strength of the individual spans of the helix wire is found
to be the most important single factor in the mechanical
strength of the grid described above. Y
It has been pointed out above that the siderods and
helix Vwire intersect to form approximaterectangles. In
' accordance with this invention and as shown in FIG. 2, ..
y lthere is ïadded to the conventional structures, another
helix, or truss wire 10, of different pitch, which >tends to
form appproximate triangles 13 and which stiffens Ythe
structure. The truss wire 10 in the embodiment shown
in FIG. 2, is in the form of a coarse pitch helix in contact
e with Va regulariine pitch helix 12 so thateach turn of
the truss wire 10 crosses perhaps llû'turns of the- helixv
400 t.p.i., 0.5 rnil ____ _.
.
Do _______ __-.
This invention is also Iapplicable to a grid of the type
shown in FIG. 3. In this embodiment, the grid helix
12 is on the inside of the side rodsv 14 while the truss
Wire 1S is on the inside of the helix 12.
The dimen
sions, geometry and materials used for this embodiment
may be similar to those previously described. Also,
multiple Vtruss wires may be used as has been explained.
In accordance with my invention, the grid helix wire
and »the truss wire may be on opposite sides of the grid
side rods. As shown in FIG. 4, the side rods 1~4 have
a grid helix `12. applied inside thereof while the truss wire
11S is applied around the outside of the said side rods 14.
The said rods -1‘4 are brazed to both the grid helix and
the truss wire. Also, as shown in IFIG. 4, four truss
wires are used in quadruple thread. The pitch of the
grid helix is fine compared to the pitch of the truss wire
18 in a similar manner to the relative pitches disclosed
in connection withy FIGS. 2 and 3 hereof.
Further, inv accordance with my invention, the truss
Wire 12. ySurprising improvements have been observed 'bewire :18 may be between the side rods 14 and the grid
cause of this structure, considering the small amount of 40 helix 12 and may be brazed to both thereof, as illus
wire that hasV been added and the negligible effect on
trated in FIG. 5. This ligure also shows four truss wires
electrical characteristics.
wound in multiple thread.
The truss wire I10 is preferably the same diameter as the
FIG. l6 is a partial sectional view of a tube embodying
helix wire '12, although it is shown as a smaller diameter
this invention. The tube includes a cathode member 20,
wire for simplicity ofV illustration, so that there is little 45 a grid 22 and an anode 24 all of which are ruggedly
disturbance of dimensions at the cross-over points be
supported at one end on flanges l26, 28 and 30 respec
tween theY truss and helix wires. The regular helix 12 has
tively. The flanges referred to have an appreciable lateral
the proper inside diameter except in the immediate vicin
extent and each is supported adjacent its periphery by a
Vity of a cross-over point. Tests indicate that it is equally
tripod array of lead-in and support wires 32 firmly fixed
effective to place the truss wire 10 between the helix 12 50 to a wafer 34. It should be noticed that the upper end of
and the siderods 14. Although it is less Veffective for the
the grid' 22 _is free and would be susceptible to certain
stiifening purposes to place the truss wire over the side-V
mechanical movements, as has been explained, which in
rods, this is of special conveniencein manufacturing.
Manyv tests have shown that the »truss wire 10 is most
eifective if the turns-per-inch of the truss wire is such
that the pitch (reciprocal of the turns per inch) is in the
turn would cause spurious electrical outputs, were it not
forl the presence of the truss wires 10, 16 and 11S in
accordance with this invention.
It should be understood that the tube shown in FIG.
range of from one~third of Áto equal to the circumference
6 is exemplary and that this invention is also applicable
of the grid. The use of multiple truss wires 16 and d8 as f - to other tubes, such as power> tubes, having a grid of the
in a double or triple thread, is particularly advantageous.
cylindrical multiple siderod, cantilever supported type.
As shown in the following table, each additional truss Wire 60 What is claimed is:
'
,
16 and 118 gave the same percentage improvement as
. 1. A cylindrical type grid structure comprising a plu
characterizedV in the previous one. The table shown
rality of siderods, a helix wire having a relatively large
below summarizes these -tests as well as the effect of
number of turns per inch joined to said siderods, and a
varying the truss wire diameter. Other `tests have shown
ytruss wire having a relatively small number of turns per
that the vibrations decay more rapidly in the grids having 65 inch joined to at least one of said helix Wire and said
truss> wires. These multiple truss wiresaltl, 16 and 18
(IFIG. 1)'permit the use of near optimum turns-per-inch
plurality of siderods.
.
2, A grid structure as in claim 1, wherein said truss
of each wire and yet more stiffening effect may ïbe
achieved. e That is, a greater number of srtuctural tri
wire is between said helix wireyand said plurality of
angles isvformed by truss wires crossing at a favorable 70
3. A grid structure as in claim l, wherein said helix
wire is within said plurality of siderods, and said truss
wire is around said plurality of siderods.
V4. A cylindrical type grid structure of the cantilever
supported type comprising a plurality of siderods, a helix
grid wire having between 100 and 500 turns per inch
anglerto make strong triangles. Accordingly, the several
truss wires should be spaced quite uniformly although no
severe tolerance or uniformity of spacing is involved.
_ One interesting result, thathas been found, 4and that
is shown in the table, is that there is little advantage to
siderods.
~
3,041,495
6
brazed to said plurality of siderods, and between 1 and
4 truss wires each in the form of a helix having 5 to 15
`turns per inch brazed to at least one of said helix grid
wire and said plurality of siderods.
5. A grid structure as in claim 4, wherein said truss
helix joined lto one of said grid Wire helix and said
siderods, said truss wire having a relatively small number
of turns per inch and forming a plurality of triangular
configurations with said grid W-ire helix and said siderods.
9. A cantilever supported, cylindrical type grid struc~
ture comprising a plurality of side rods, a grid Wire helix
bonded to said siderods and having a relatively iine pitch,
wire has a diameter at most equal to the diameter of said
helix wire.
a truss wire helix secured to one of said grid Wire helix
6. A grid mount comprising a support structure, a
and said plurality of siderods, the pitch of said -truss wire
tubular grid mounted at one end thereof only on said
support structure, said support structure having an an 10 being within the approximate range of one third of the
circumference of said grid structure to equal the circum
nular iìange of larger transverse extent than said grid, a
ference of said grid structure.
wafer of insulating material, three parallel support rods
10. A cylindrical type grid structure comprising a plu
iixed to said Wafer and iixedly engaging at one group of
adjacent ends thereof regions of said iiange equidistantly
spaced therearound, said grid comprising a plurality of
rality of side rods, a helix Wire having a relatively large
number of turns per inch and a plurality of truss Wires
parallel siderods yand a helix íixed to said rods, said helix
having a relatively large number of turns per inch, and
means for restraining vibrations of the other end of said
grid, said means comprising a wire helix having relatively
small number of turns per inch iixed to -said grid and 20
having a relatively small number of turns per inch helically
wound in multiple lthread arrangement, said side rods,
said helix wire `and said truss Wires being electrically
and mechanically joined to each other at points along
being substantially coextensive axially therewith.
11. A grid structure such as in claimed in claim 10
in Which said plurality of truss Wires is four.
7. A grid mount comprising a cylindrical grid having
their lengths.
12. A cylindrical type grid structure comprising a plu
a plurality of parallel siderods and a wire helix having a
rality of side rods, a helix wire having a relatively large
relatively large number of turns per inch and fixed `to
said siderods, means for ruggedly supporting one end of 25 number of turns per inch, a truss Wire wound in a helix
and having a relatively small number of turns present
said grid, said means comprising an annular flange mem
per inch, said side rods, said helix Wire and said truss
ber, said siderods being spaced equidistantly around said
wire being electrically and mechanically joined to each
flange and disposed in a circle having a larger diameter
other at points along their lengths.
than said helix, and additional means for extending the
support of said one end of the grid to the other end 30
References Cited in the tile of this patent
thereof, said additional means comprising a wire helix
having a relatively small number of turns per inch fixed
UNITED STATES PATENTS
to said grid and in coextensive relation therewith.
8. A cylindrical type »grid structure comprising a plu
1,780,033
rality of siderods, a grid Wire helix having a relatively 35 2,438,113
2,457,626
large number of turns per inch joined to said plurality
2,489,873
of siderods and forming a plurality of approximately
rectangular coniigurations with said siderods, a truss Wire
Nolte _______________ __ Oct.
vDenmark ___________ _.. Mar.
Atlee _______________ __ Dec.
Thorson __________ __v__ Nov.
28, 1930
23, 1948
28, 1948
29, 1949
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