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Патент USA US2135034

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Nov. 1, 1938.
'
_
c. w. HANSELL.
REDUCTION OF TUBE NOISES
2,135,034
I
Filed Jan. 28, 1935
AUD/O
OUTPUT
A
w
INVENTOR
CLARENCE W. HA A/JELL
BYWggWM/
ATTORN EY
2,135,034
‘ Patented Nov. 1, 1938
UNITED STATES PATENT OFFICE
V
g
,
2,135,034
REDUCTION OF TUBE Noises
Clarence W. Hansell, Port Jefferson, N..Y., as
signor to Radio Corporation of America, a cor
poration of Delaware
Application January 28, 1935, Serial No. 3,692
6 Claims. (Cl. 179—171)
This invention relates to a novel method of
and circuit for operating thermionic tubes in
cluding a method of and means for obtaining
more quiet operation of thermionic tubes in re
5 lay or ampli?er circuits than has been possible
heretofore.
.
If in any tube there is a grid between the oath-
ode and anode which is operated at positive po
tential then there will be a flow of current to
this grid in which should appear ?uctuations cor
responding to the ?uctuations in current between
the cathode and anode. If the circuit between
this positively charged grid and the ?lament
contains a high series impedance adjacent the
15 grid or such an impedance is in the ?lament re
turn or a circuit tuned to the frequency at'which
the tube is being operated is placed in either of
said positions, the ?uctuations in current ?owing
from the ?lament will be smoothed .out. by the
20 choking action and prevented, or reduced to a
low value, and there will be instead ?uctuations
in potential between the ?lament and said grid.
This ?uctuation in potential will tend to prevent
variations in the current ?owing to and through
25 the grid. That is, it will reduce the effect of‘al
ternating cathode heating current fluctuations in
cathode emission and initial electron velocities
and shot effect.
' If the wanted variations, e. g., variations caused
by or productive of signalling currents‘, in anode
current also cause variations in electron current
leaving the cathode then the means described
above acting on the grid will tend to cause de
generation by opposing or reducingthis useful
flow as described above. This may reduce the
useful output from the tube in the same ratio
as the reduction in tube noise. However, I pro
pose to so construct and use the tube that there
is a storage of electrons or space charge outside
Al) the grid which encloses the ?lament and the use
45
At very high frequencies; the charge stored in
the space surrounding the space charge grid will
be more than sufficient to supply all the varia
tions ‘in anode current needed without too much
diminution of the charge during current peaks. :
The novel features of my method and circuit
have been set forth with particularity in the
claims appended hereto.
'
The nature of ‘my invention and the mode of
operation of thesame will be best understood 11:0
from the following. detailed description thereof
when read in connection with the drawing,
throughout which like reference characters indi
cate like parts, and in which:
'.
Figures 1 to '3 inclusive sho-W "various circuit 15
arrangements for carrying out the principles of
my invention.
.
‘
The invention is applicable to relays, ampli
?ers, modulators or demodulators, and the po
tentials involved may be of any frequency.
Referring to the drawing,‘ in Figure 1, I have
shown a circuit by means of which quiet and'ef?
'cient ampli?cation of audio frequencies may be
obtained.
1
'In Figure 1, 2 is ‘a thermionic ‘tube having a 25
control grid 4,_an inner-grid 6, an anode 8, and
a cathode 5. Qrdinarily these electrodes will be
constructed concentrically and in said structure
the space charge grid 5 will surround the cathode.
The control grid 4 is coupled, as shown, by way
of a transformer H! to any source of low fre
quency alternating current which :it is desired
to amplify. The control grid 4 is maintained at
the desired negative potential by a battery H
connected, as shown, with its negative terminal
towards the control grid 4 and its positive termi
nal to ground.
‘
.
The inner-grid 6 may be maintained at posi
tive potential with respect to the cathode or may
ful anode current variation will ?ow from' this
be connected to ground, as shown, while the
cathode 5 is maintained negative with respect to
storage reservoir. In other words, the volume
of space surrounding the space charge grid will
ground by means of the source It connected, as
shown. The cathode 5 is energized by a source
act as a virtual cathode, spaced from the heated
surface of the real cathode, insofar asthe useful
functions of the tube are concerned. Now if the
variations in cathode emission are prevented or
reduced as described in the preceding paragraph
there will be no degenerative effect on the useful
output which depends on the stored electrons
rather than on rate of emission; This space will
be fed with a constant flow of electrons from the
?lament equal to the average plate current while,
at the same time, it acts as a reservoir to accom~ '
55 modate the useful variations in plate current.
5
of energy such as an accumulator or recti?er, or
as shown, by output from an alternating current
transformer T, and the cathode energizing cir
cuit includes the audio frequency choke M which
is of high impedanoeto- the oscillations-from ‘ID.
If desired the cathode may be heated by an in
sulated heater, inside 3a coated cathode, to sepa
rate the heating and cathode circuits.- In this
case a choke may be included only in the connec
tion to the cathode. This choke has high im
pedance at the frequency to be relayed, that is,
at the frequency of the input oscillations from 55
2,135,034
2
l0 and prevents ?uctuations in the electron cur
rent ,?owing from the cathode. Consequently
the audio frequency choke coils M' prevent the
noises which would normally result from the
?uctuating cathode emission.
At the same time
the direct current potential difference between
the cathode 5 and the inner-grid 6 insures a con
stant ?ow of electron current to and through the
grid 6 and, consequently, a space charge or store
10 of electrons is built up between the inner grid 8
and outer grid 4. So long as the outer grid 4
remains at a constant negative potential there
electrode SG is interposed between the control
grid 4 and the anode to further insure quiet op
eration by preventing anode potential variations
at the signal frequency to be ampli?ed, from
reaching the control grid, space charge grid, or '
cathode. The shielding grid SG is maintained at
the desired positive potential by connecting the
same to the positive terminal of the source by
way of a resistance 21, as shown. Radio fre
quency oscillations are by-passed around the re
10
sistance 27 and the source by means of by-pass
ing condenser C connected as shown.
will be a constant ?ow of current to the anode. .
Here, as in Fig.2, the inductances 24 in the
When the audio frequency potentials to be re
cathode heating circuit are tuned by the capac
15 layed are impressed on the‘outer grid, the cur
itor 26 to the frequency of the oscillations to be 15
rent to the anodeelectrode will vary also and . ampli?ed. Here, as in Fig. 2, it is assumed that
there will be a useful output from the tube which radio frequency oscillations are to be ampli?ed,
will appear in the transformer I2. This output
and the input and output circuits are tuned to
will be relatively free from noises produced by the frequency of said oscillations.
20 alternating current heating energy, or direct cur
Having thus described my invention and the 20
rent on which alternating current components operation thereof, what I claim is:
are superposed, thermal agitation and varying
1. In a thermionic relay, an evacuated enve
emission from the cathode. In this case’ the lope enclosing a control grid electrode, a cathode,
?uctuations in anode current are obtained pri
an anode, and an auxiliary electrode located ad
25 marily from ?uctuations in the current ?owing
jacent said cathode, a circuit for applying al 25
to the space charge grid but not to any appre
ternating currentpotentials between the control
ciable extent from ?uctuations in electron cur
grid and auxiliary electrode, a load circuit con
rent from the cathode. At very high frequencies nected between the anode and cathode, a circuit
the ?uctuations’ will come primarily from the connecting said auxiliary electrode to said cath
30 electron cloud or space charge outside the. space
ode, said circuit including means for maintaining 30
charge grid.’ Thus, at low frequencies, the space said auxiliary electrode at a potential relative to
charge grid becomes a virtual cathode while at said cathode such that a large ?ow of thermionic
very high frequencies the electron cloud or space current from said cathode to said auxiliary elec
charge near the space‘ charge grid absorbs the trode is produced, and means for preventing
35 current. ?uctuations and becomes the virtual
?uctuations in the current ?owing from said
cathode including an inductive reactance in said
Of course, the present invention maybe ap
auxiliary electrode-cathode circuit of high im
plied to a wide number of circuits and the cir
pedance to current changes at the frequency of
cuit of Fig. 1 may be modi?ed considerably with
the alternating current to be relayed, said
40 out departing from the spirit of the present in
means also producing potential variations be
vention. For example, a circuit as shown in Fig.
tween said auxiliary electrode and cathode which
2 including a neutralized ampli?er tube, may be tend to prevent ?uctuations in current ?ow from
said cathode to said auxiliary grid.
In Fig. 2 it is assumed that radio frequency
2. In a thermionic relay, an evacuated en
potentials
are
to
be
relayed
or
ampli?ed.
In
Fig.
45
velope enclosing a control grid electrode, a cath
2 the potentials to be ampli?ed are applied, as
ode, an anode, and an auxiliary electrode adja
shown, by transformer 20 tothe control grid 4, cent said cathode, a tuned circuit for applying
and the radio frequency oscillations may be de
alternating current potentials between the con
rived from the output of transformer 22, con
trol grid and said auxiliary electrode, a tuned
nected with the anode of tube‘2. The control circuit connected between the anode and cath 50
grid 4 is connected by way of the secondary ode, said auxiliary electrode being connected
winding of the transformer 20 'to ground, while with said cathode by means for maintaining
the space charge grid is connected directly to said auxiliary electrode at a potential relative
ground. The input and output circuits are, as to said cathode at which there is a large ?ow
55 shown, tuned to the radio frequency to be am
of electrons to said auxiliary electrode, and 55
pli?ed. The cathode heating circuit includes ra
means for preventing ?uctuations in the ?ow of
dio frequency impedances 24 connected, as electrons from said cathode to- said auxiliary
shown, and tuned to the frequency of the oscil
electrode, including reactances in said auxiliary
lations to be ampli?ed by a tuning capacity 26.
electrode-cathode.circuit, said reactances being
In
this
modi?cation
the
operation
is
the
same
60
tuned to the frequency of the alternating cur 60
as in the modi?cation shown in Fig. 1. The rent to be relayed, said means also producing po
tuned impedances 24, prevent ?uctuations in the tential variations between said auxiliary elec
cathode emission at the frequency of the oscil
trode and cathode which tend to prevent ?uc
lations to be ampli?ed. The potential of the tuations in current ?ow from said cathode to
65
65 electrode 6 with respect to the cathode 5 builds said auxiliary grid.
.
cathode.
used.
'
'
.
‘
‘
up a space charge and stores up electrons in the
space around the electrode 6 which insure the
desired useful stream of electrons‘ to the anode
to amplify or relay the potential variations. The
70 capacity between the anode and grid electrodes
may be balanced tothe desired degree by the
capacitor NC.
-
V
'
.3. In a signalling system, an electron dis
charge tube having an anode, a control electrode,
an auxiliary electrode, and a cathode adjacent
said auxiliary electrode, means for applying sig
nalling potentials between the control electrode 70'
and the auxiliary electrode, Vacathode heating
source, means including a bias potential source
The modi?cation shown in Fig. 3 is similar in
many respects to the modi?cation shown in Fig.
in a ‘circuit connecting said cathode heating
source to said auxiliary electrode for maintaining
2.
said auxiliary electrode at a'potential such that 75
Here, however, an additional screening grid
3
2,135,034
a large flow of current to said auxiliary electrode
from said cathode takes place, whereby said aux
iliary electrode forms a virtual cathode, and
means including an inductive impedance for pree
said emission element such that a large concen
trationof electrons takes place on and around
venting the effect of, said' signalling potentials
said auxiliary electrode whereby the same acts as
upon the emissiveness of said cathode, said im
pedance being connected at one end to said cath
ode and at the other end to said circuit which
interconnects the cathode heating source and
10 the auxiliary electrode biasing means.
4. In a signalling system, a tube having an out
15
tential variations, and means for maintaining
said auxiliary electrode at a potential relative to
a virtual cathode.
5. A system as recited in claim 4 wherein said
means in said heating circuit for converting ?uc
tuations in current therein into potential vari
ations is an impedance the value of which is high 1O
with respect to the alternating currents applied
put electrode, an electron emission electrode, an
to said control grid.
auxiliary electrode adjacent said electron emis
sion electrode and a control electrode,gmeans for
6. A system as recited in claim 4 wherein said
means in said heating current circuit for con»
applying alternating current ‘potentials to said
verting ?uctuations in current therein into po
7
15
tentlalvariations comprises reactances‘tuned to
control electrode, means for supplying alternat
ing current potentialsvfrom said output electrode‘ the frequency of the, alternating current im
pressed upon said ‘grid circuit.
a heating circuit for said electron emission elec
trode, means in said heating circuit ‘for convert
20 ing ?uctuations of the currenttherein into po
' CLARENCE w. HANSELL.
20
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