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Патент USA US2122772

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July 5, 193s.
2,122,772
E. GREEN
THERMIONIC AMPLIFIERFiled Oct. 29, 1932
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July 5, 1938. v
E_ GREEN
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2,122,772
THERMIONIC AMPLIFIER
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Filed Oct. 29, 1952
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INVENTOR
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ERNEST G
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ATTORNEY
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Patented July 5, 1938
2,122,772
UNITED STATES
PATENT OFFIQE
2,122,772
THERMONIC' AMPLIFIER
Ernest Green, Chelmsford, England, assigner to
Radio Corporation of America, a, corporation
of Delaware
Application October 29, 1932, Serial No. 640,280
In Great Britain October 29, 1931
3'v Claims.
(Cl. 179-171)
This invention relates to thermionic amplifiers
and more particularly to thermionic amplifiers of
what may be termed the multi-tube or multi-valve
per stage type i. e. amplifiers wherein a plurality
5 of tubes are provided in a single stage of ampli
flcation.
In thermionic ampliiiers embodying a plurality
of tubes in a single stage of amplification, and as
at present in common use, difficulty is often eX
perienced in practice, owing to the fact that the
individual tubes will not share the alternating
current load equally unless their electrical char
acteristics are identical.
For example, where a
single stage of ampliiication comprises a plu
15 rality of triodes in parallel, if theseparate tubes
are of slightly different internal characteristics
they will not ordinarily share the alternating cur
rent load equally with one another. For this
reason it is usual to require that tubes which are
20 intended to work together in a single multi
tube stage, shall be “matched”, but this is always
a more or less expensive requirement, and where
large tubes are in question the additional ex
penditure may be prohibitive.
Similar requirements as regards “matching”
25 for alternating current load apply not only to par
allel tube circuits but also to so-called push
pull circuits as ordinarily employed.
It is, of course, also desirable in most cases to
“match” as regards the direct current compo
3 O nents of anode or plate current, but this presents
no difliculties, and may be accomplished quite
simply by the usual method of providing where
necessary, different values of grid bias for the
different tubes e. g. by providing grid bias bat
35
teries of diiferent Values for the different tubes
or, where automatic grid bias is in question, by
arranging the tube grid circuits to receive dif
ferent values of potential from a grid biasing
ceding stage of amplification or other source of
Voltage to be amplified that the input alternat
ing current voltage applied to different tubes is
different and is in each case suited or adjusted to
the characteristics of the tube in question, so that
the said tube will take its correct proportion of
the total alternating current load.
The invention is illustrated in and explained
in connection with the accompanying drawings
which show diagrammatically various arrange 10
ments in accordance therewith.
Fig. l is a circuit diagram of a parallel con
nected resistance coupled ampliiier;
Fig. 2 is a diagram of a theoretical circuit of
the input voltages;
15
Fig. 3 is a circuit diagram which is a modiñ
cation of Fig. l;
Fig. 4 is a circuit diagram of a transformer
coupled ampliiier;
Fig. 5 is a circuit diagram of a push-pull ampli
20
lier;
Fig. 5 is a circuit diagram of another modifi
cation of the circuit arrangement shown in Fig. 3.
Referring now to Figure l which shows one way
of carrying out the invention, a parallel anode
connected resistance-capactiy coupled thermionic
ampliñer comprises an input impedance consist
ing of the usual resistance M one end of which
is connected at GB- to the negative terminal of
a suitable grid bias source (not shown) and the 30
other end of which is connected through the
usual coupling capacity C1 to a preceding stage
or other source of voltage to be ampliñed. The
parallel stage now described consists of three
triodes V1 V2 V3 in parallel (though of course
there may be any other number of tubes) the
anodes of the triodes being connected together
and through an anode resistance R to the posi
tive terminal of a source of anode potential (not
vide an improved arrangement whereby the ne
shown) the junction point of the anode resistance 40
R and the anodes being also connected through
the customary coupling condenser C2 to the next
cessity for accurately “matching” thermionic
stage.
40 resistance or its equivalent.
The present invention has for its object to pro
tubes in a multi-tube amplifier stage is avoided.
The invention is applicable alike to parallel tube
45
The three grids of the tubes are eifectively con
nected each to a different tapping point T1 T2 or
T3 on the input resistance M the leads to the grids
a degree of balance of such accuracy as to render
of the tubes Vi, V2, containing each a supple
mentary bias battery b1 or b2 to maintain equal
direct current anode feeds to the three tubes.
circuits and push-pull tube circuits and provides
the said invention applicable to circuits of large
power. This applicability to circuits of large
50 power is very important for it will be appreciated
that, for example, in the case of tubes in parallel,
it is possible if any substantial disparity be
tween tubes exists, for the individual alternat
ing current loads of the tubes to Vary so much so
that in some circumstances the load on some of
the tubes may even be negative, i. e. some of the
tubes may “drive” the others.
According to this invention, the input elec
trodes of a plurality of tubes arranged in a com
60 mon amplifying stage are so connected to a pre
The cathodes are connected together and to thei ‘
negative terminal of the anode potential source
in the usual way.
The above described circuit is, from the point
of view of the present invention, the electrical
equivalent of the theoretical circuit shown in
Figure 2 which theoretical circuit consists of a
plurality of parallel paths each path consisting
of an alternator, and a resistance in series, the
three parallel paths being in parallel across a
common load resistance R. The voltage of the 60
2
2,122,772
alternator in each branch of the equivalent cir
cuit is, as indicated in Figure 2, the product of
the alternating input voltage eg1 or e‘gz or egg to
the appropriate tube multiplied by the amplifica
tion factor 1u, ,uz or ¿la of that tube.
The resistances in series with the equivalent
vand the output from the stage is taken off as in
the usual way through an output transformer OT
whose primary is connected between the common
anode point and the high tension source (not
shown).
In a still further circuit modification shown in
alternators are the internal resistances of the ' Figure 5' in which the invention is applied to a
tubes in question and are represented by R1, R2,
by R.
In carrying out the present invention the input
four tube amplifier consisting of two tubes V1”’,
Vz'”, and V3”’, V4”’ in parallel and two (V1”’
Va’" and V2”' V4"’) in push pull each grid is
coupled through its own coupling condenser Cl'",
tapping points are so chosen that the terminal
voltages across all the alternator-resistance
secondary TS of an input transformer the “push”
R3.
10
The common load resistance is represented
branches in the equivalent circuit are equal when
the load is shared equally. This condition is ob
viously satisfied when the proper bias battery
values are chosen and the direct current through
the tube equalized a condition for obtaining equal
alternating current through the tubes will then
20 be where
. etc.
or expressed in general terms for the case Where
there are n tubes
.
tubes being connected to different tapping points
upon one side of the electrical centre EC of the
transformer secondary and the two “pull” tubes
being connected to points upon the other side of
the electrical centre. Each grid is also directly
connected to its o-Wn grid resistance R91 Rg‘z Rgs
or R94 the other end of which is connected to a 20
suitable point upon a common bias battery B”
the cathodes of the four tubes being connected
together and to the electrical centre of the trans
former secondary. The output circuit of the
stage consists of a centre tapped output trans 25
former OT’ arranged as in the usual way.
Figure 6 of the accompanying drawings shows
30
The above condition is the condition for ac
curate adjustment. Clearly however, when the
value of R is very much greater than a tube re
sistance divided by the number of tubes suñicient
accuracy will be obtained by making
_eene
Cz'", 03”’ or 04"’ to a different tapping upon the `
a still further circuit arrangement in accordance
with this invention, this circuit being a modifica
tion of the arrangement shown in Figure 3. In
Figure 6, V1’ V2’ V3’ are three tubes connected
in parallel, each tube having a separate grid re
sistance R91 R92 or Roa the ends of these resist
ances remote from the respective grids being
connected to tapping points upon a common bias 35
battery B..
Input to the grids of the tubes V1'
V2’ V3’ is taken through coupling condensers C1’
.
.
etC.
Figure 3 shows a circuit of a modification
40
which is suitable for use as the main modulator
stage of a choke controlled modulated carrier
wave circuit having input modulating potentials
which are applied across three condenser cir
cuits. The condensers are connected at the side
of the preceding stage in parallel, each con
denser circuit consisting of a condenser C1',
Y C2’ or C3’ connected on the grid side in series
with a resistance Rc1-Roz or Rga the other end
50 of which is connected to a point on a common
grid bias battery B. The modulator stage con
sists of a plurality of tubes V1’ V2’ V3’ hav
ing their anodes connected in parallel, each grid
is connected to a tapping point T1’ T2’ or T3’
55 upon the appropriate resistance there being, of
course, as many parallel input condenser circuits
as there are tubes. The anodes of the tubes
are connected together and through a choke L
to the positive terminal of the anode potential
60 source (not shown) the high frequency stage
HFS to be modulated being connected as in the
usual way between the common anode point and
the common cathode point of the modulator
stage.
The invention is also applicable to transformer
C2’ C3' from tapping points T1’ T2’ T3’ upon an
anode resistance AR connected in the plate cir
cuit of a preceding tube PV.
40
The invention is obviously applicable to stages
consisting of any desired member of tubes in par
allel or in push-pull or any combination of par
allel and push-pull.
Having now particularly described and ascer
tained the nature of my said invention and in
what manner the same is to be performed I de
clare that what I claim is:
1. An amplifying system comprising a plurality
of tubes, each having an anode, a cathode and
a grid, means connecting the anodes’of the tubes
directly in parallel, means connecting together
the cathodes of said tubes, an alternating cur
rent output circuit connected between the par
allelly connected anodes and said cathodes, an
alternating current input circuit, means con
necting the cathodes of said tubes to said input
circuit, means connecting the grids of said tubes
to points of different alternating current po
tential in said input circuit, and means for sub 60
jecting each grid to a different direct current po
tential with respect to its associated cathode.
2. An amplifying system as described in claim
1 characterized by the fact that the grids are
connected to the input circuit by way of a plu
coupled amplifiers and in one such circuit ar~
rality of direct current blocking condensers.
rangement shown in Figure 4, the grid of each
tube V1", V2”, Vs” of a parallel connected stage
is connected through a coupling condenser C1',
3. An amplifying system as described in claim
1 characterized by the fact that the input circuit
comprises a transformer, and also by the fact
that the grids are connected to the secondary of
said transformer by way of a plurality of direct
current blocking condensers.
70 C2', C3’ to a different point on the tapped sec
ondary TS of an input transformer. The grid
side of each coupling condenser is connected
througha separate resistance R1”,»R2”, R3" to
a suitable point on a common bias battery B'
ERNEST GREEN.
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