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Патент USA US2117949

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May717, 1938.
2,117,949
G. W’ FYLER
AMPLIFIER NEUTRALIZING SYSTEM
Filed June 22, 1935
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Patented May 17, 1938
2,117,949
UNITED STATES PATENT OFFICE
2,117,949
AMPLIFIER NEUTRALIZING SYSTEM
George W. Fyler, Schenectady, N. Y., assignor to
General Electric Company, a corporation of
New York
Application June 22, 1935, Serial No. 27,899
6 Claims.
(Cl. 179—171)
My invention relates to electron discharge tube
ampli?ers, and more particularly to ampli?ers of
the type comprising two electron discharge de
vices connected in push-pull relation and pro
5 vided with neutralizing circuits for preventing
coupling between the input and output circuits
due to the inter-electrode capacity existing in
the tubes.
The use of neutralizing connections for pre~
~ 10 venting inter-electrode capacity coupling between
the output and input circuits of a push-pull con
nected ampli?er is well known. Such neutral“
izing connections usually comprise a neutralizing
condenser connected between the control grid of
‘15 each tube and the anode of the other tube.
It
is desirable in ampli?ers of this type to employ
neutralizing condensers of ?xed capacity, and
this is particularly true in large power installa
tions where the size of the condensers required
20 would make the cost of variable capacitors pro
hibitive. However, it has been found that if ?xed
neutralizing condensers be used some method of
making minor adjustments must be provided if
satisfactory neutralization is to be obtained. The
25 necessity for such adjustment is due primarily
to variations in the characteristics of the tubes
and condensers used in the construction of such
ampli?ers. Because of the manufacturing toler
ances allowed in the manufacture of such appa
30 ratus it is di?icult to obtain tubes and condensers
having characteristics which are identical, and
which conform exactly to the characteristics spec~
i?ed by the manufacturer. The effect of stray
electromagnetic and electrostatic coupling be
tween the circuit leads in the input and output
circuits of ampli?ers of this type must also be
neutralized if satisfactory operation is to be ob
tained.
In accordance with my invention the advan~
40 tage of using ?xed neutralizing condensers is re
tained and, at the same time, a means is provided
whereby the minor adjustments necessary to ob
tain substantially perfect neutralization may eas
ily be made.
45
It is an object of my invention to provide in
an ampli?er of the push~pull connected type an
connected respectively in each of the circuits and
arranged in adjustable inductive relation.
More speci?cally, it is an object of my inven
tion to provide an arrangement of the above type
in which portions of the neutralizing circuit con
ductors are arranged in inductive relation and
mounted on a mechanical supporting structure
whereby the portions of the conductors may be
moved relative to one another to change the mu
tual inductance therebetween.
10
The novel features which I believe to be char“
acteristic of my invention are set forth with par
ticularity in the appended claims. My inven
tion itself, however, both as to its organization
and method of operation together with further 15
objects and advantages thereof will best be un~
derstood by reference to the following speci?ca
tion taken in connection with the accompanying
drawing in which Fig. 1 shows an ampli?er of
the push-pull type having my invention embodied 20
therein, and Fig. 2 shows the equivalent bridge
circuit of the circuit shown in Fig. 1.
Referring to Fig. 1 of the drawing I have shown
an ampli?er system connected in push-pull rela
tion and arranged to be controlled by a source of 25
oscillations, as for example the output from a
carrier wave oscillation generator, impressed on
the primary winding of the transformer l and
to supply its ampli?ed output to the primary
winding of a coupling transformer 2. The sec- 30
onclary of the transformer I has its two ends con
nected respectively to the control grids of the
electron discharge tubes 3 and 4. The mid—point
of the secondary of the transformer l is connected
to a common cathode lead 6 of the tubes 3 and 4 35
through the ground connections indicated at 5.
The respective anodes of the tubes 3 and 4 are
connected to the two ends of the primary wind
ing of the transformer 2; which primary has its
central point connected to the common cathode ‘*0
lead 6 through the source of plate potential 1.
The output circuit of the ampli?er may be tuned
to the operating carrier frequency by a variable
condenser 8.
4
The operation of the above-described ampli?er
improved inter-electrode capacity coupling neu
tralizing system which includes an inductance in
the neutralizing circuits which is adjustable to
obtain substantially complete neutralization of
the inter-electrode capacity coupling between ‘the
output and input circuits of the ampli?er.
Brie?y described, as ‘the oscillating input poten
tial impressed on the primary winding of the 50
transformer l alternates between positive and
negative values the tubes 3 and 4 alternately sup
It is a further object of my invention to pro
vide in a push-pull connected ampli?er a pair of
output circuit.
neutralizing circuits which include conductors
is well understood in the art and only a short ex
planation thereof is deemed to be necessary.
ply an ampli?ed output current to the ampli?er
The outputs from the two tubes
.re combined in the tuned output circuit includ~ 55
2,117,949
2
ing the primary of the transformer E‘. and are
impressed on the secondary thereof.
In order to prevent any coupling between the
input and output circuits of the system the neu
tralizing currents flowing to the control grids of
the tubes is increased.
In like manner, if the
inductive reactance is decreased by decreasing
the mutual effects between the conductors I3 and
M, the capacitive reactance in each of the circuits
8 and If} is increased and the magnitude of the
clude respectively the ?xed neutralizing con
neutralizing currents flowing to the grids of the
densers H and i2. It will be noted that the neu
tubes 3 and 4 is decreased. It will of course be
tralizing circuit 9 is connected between the con
trol grid of the tube 3 and the anode of the tube understood that the value of the mutual induct
ance between the conductors l3 and I4 and the 10
10 4. In like manner the neutralizing circuit IE] is required adjustment thereof are quite small, due
connected between the control grid of the tube 4
to the high operating frequencies and the fairly
and the anode of the tube 3.
The effect of the two neutralizing circuits is‘ and 'close approach to complete neutralization nor
I0 is to supply currents to the control grids of mally obtained in a properly designed system.
In this connection it will be appreciated that neu 15
the
two tubes 3 and 4 which are equal in magni
15
tude and opposite in phase to the currents ?owing tralizing condensers I! and I2 having a capacity
reactance value slightly higher than the calculat
between the input and output circuits of the am
pli?er through the coupling therebetween formed ed value should be used. This is necessary since
by the capacity existing between the control grid the reactance of the coupled conductors l3 and
I4 is substantially purely inductive and an in 20
20 and anode of each of the two tubes. In this man
tralizing circuits 9 and it are provided which in
' ner interelectrode capacity coupling between the
input .and output circuits of the ampli?er system
is minimized.
It has been found in neutralizing systems of the
25 type described, in which ?xed neutralizing con
densers are employed, that satisfactory neutral
ization cannot be obtained unless a suitable means
is provided for making minor adjustments in the
neutralizing circuits after the ampli?er has been
assembled and dining its testing operations.
This may be attributed to the fact that an ac
curate calculation of the neutralizing current
necessary to satisfactory neutralization cannot
be made. Manufacturing discrepancies in the
35 construction of the elements used in the system,
together with stray electrostatic and electromag
netic effects render an exact determination of
the magnitude of the required neutralizing cur
rent practically impossible.
40
In order to overcome the above-described dil
?culty I provide a device for making minor ad
justments which includes a pair of conductors l3
and I4 respectively forming a part of the two
neutralizing circuits 9 and it, the two conduc
. tors being arranged in inductive relation and
suitably mounted for relative movement there
between. I have shown the conductors l3 and
M as comprising simply portions of the neutraliz
ing leads and have indicated these conductors as
so being mounted on a supporting member shown
diagrammatically at I5; the conductor l4 being
adjustably mounted on the supporting member
l5 by means of the two adjusting screws l6 and
H, and the conductor l3 being ?xedly mounted
thereon by means of insulators indicated at 58.
It will of course be understood that any other
suitable mounting arrangement may be em
ployed and, further, that the conductors i3 and
I4 may be arranged in any desired manner so
60 long
as they are maintained in inductively
coupled relation.
With the above arrangement accurate neutral
ization of the system described may be obtained
by moving the conductors i3 and i4 relative to
each other to change the mutual inductance
therebetween. As the mutual inductance is
varied the amount of inductive reactance includ
ed in each of the neutralizing ‘circuits is varied,
thereby causing a variation in the value of the
effective capacitive reactance in an opposite sense.
Thus, if the inductance in each of the neutraliz
ing circuits 9 and H3, is increased, the capacitive
reactance is decreased by an equal amount and
the total impedance in each of the two circuits
75 thereby being lowered, the magnitude of the neu
crease or decrease in the value thereof simply de
termines the amount by which the capacity re
actance of the condensers H and I2 is decreased.
The advantages of my improved neutralizing
arrangement will be apparent from a ‘considera 25
tion of Fig. 2 wherein I have shown the equiva
lent bridge circuit for the system shown in Fig. 1
and described above. In the bridge circuit of
Fig. 2 the secondary of the input transformer l
and the primary of the output transformer 2 are 30
shown as being connected between the junction
points of the equivalent bridge formed by the
ampli?er network. The equivalent grid-anode
capacity of the tube 3 is represented by the con
denser l9 and that of the tube 4 by the condenser 35
20. The neutralizing condensers I! and I2 are
included in the opposed arms of the bridge and
the conductors l3 and M, arranged in induc
tive relation, are in series with these two con
densers.
It will be observed from an inspection of the
equivalent bridge circuit that in the absence of
the variable inductance formed by the inductively
coupled conductors l3 and [4, the magnitude of
the neutralizing currents would be ?xedly deter
mined by the value of the ?xed condensers. How
ever, by the introduction in the circuits of the
adjustable inductive reactance formed by the in
ductively coupled conductors l3 and M the effec
tive capacitive reactance in each of the neutraliz— 50
ing branches of the bridge may be varied until
it is equal to the inter-electrode capacity of the
tube being neutralized. Thus, if the inter
electrode capacities represented by the condensers
l9 and 2
are actually lower than their rated. -,
values and the actual capacity of each of the
condensers I! and I2 is higher than the speci?ed
rating, the difference may be removed by intro
ducing inductive reactance in the neutralizing
circuits sui?cient to cancel the required amount 60
of capacitive reactance therefrom,
My improved neutralizing arrangement is par
ticularly useful in those installations wherein it
is desired that the ampli?er shall operate at any
one of several different frequencies.
It has been
found that when the frequency of the potential
impressed on the input circuit of the ampli?er is
changed, a re-adjustment of the neutralizing
system is necessary if exact neutralization of
inter-electrode coupling is to be obtained. By
the provision of the adjustable inductances
formed by the conductors l3 and M the neutral
ization may be varied to obtain satisfactory op
eration over a wide band of operating frequencies.
My improved neutralizing system may be simply
3
2,117,949
and economically constructed and easily adjusted.
Thus, the only element added to the ampli?er
structure is the mechanical supporting structure
for maintaining the portions I3 and I4 of the
neutralizing conductors in the proper physical
relation.
While I have shown a particular embodiment
of my invention, it will of course be understood
that I do not wish to be limited thereto since
10 many modi?cations in the circuit may be made,
and I contemplate by the appended claims to
actance required for said neutralization, each of
said neutralizing circuits including a conductor,
said conductors having portions thereof induc
tively coupled, and means for varying the cou
pling between said portions sufliciently to produce
complete neutralization of said capacity.
4. An ampli?er comprising a pair of electron
discharge tubes each including an anode and a
control grid, push-pull input and output circuits
therefor having inter-electrode capacity requiring
cover all such modi?cations as fall within the
to be neutralized, a pair of inter-electrode capac
ity neutralizing circuits each connected between
true spirit and scope of my invention.
a grid of one tube and an anode of the other
What I claim as new and desire to secure by
15 Letters Patent of the United States, is:
1. An ampli?er comprising a pair of electron
discharge tubes each including an anode and a
control grid, push-pull input and output circuits
therefor having capacity therebetween requiring
tube, each of said neutralizing circuits including
a conductor and a neutralizing condenser, said 15
condensers providing approximately the reactance
required for said neutralization, said conductors
having portions thereof inductively coupled, and
to be neutralized, a pair of neutralizing circuits
means for varying the coupling between said
conductor portions su?iciently to produce com 20
each connected between a grid of one tube and an
plete neutralization of said capacity.
anode of the other tube, said neutralizing circuits
each including a neutralizing capacitance means
providing approximately the reactance value re
quired for said neutralization, a pair of con
ductors connected respectively in each of said
neutralizing circuits, said conductors being ar
ranged in adjustable inductive relation, and
5. An ampli?er comprising a pair of electron
discharge tubes each including an anode and a
control grid, push-pull input and output circuits
therefor, and means for neutralizing the effect 25
of the inter-electrode coupling between said in
put and output circuits, said means including a
pair of inter-electrode capacity neutralizing cir
means whereby the inductance included in each
cuits each connected between a grid of one tube
of said neutralizing circuits may be varied suffi
and an anode of the other tube, said last named 30
ciently to produce complete neutralization of said
circuits each including a conductor and a con
capacity.
denser, said condensers providing approximately
2. An ampli?er comprising a pair of electron
the reactance required for said neutralization,
discharge tubes each including an anode and a
said conductors being inductively coupled, and
control grid, push-pull input and output circuits
therefor having capacity therebetween requiring
to be neutralized, a pair of neutralizing circuits
means for varying the coupling between said 86
each connected between a grid of one tube and an
conductors suf?ciently to neutralize completely
said effect.
6. An ampli?er comprising a pair of electron
anode of the other tube, neutralizing capacitance
discharge tubes each including an anode and a
means in said neutralizing circuits providing ap
proximately the reactance required for said
neutralization, each of said neutralizing circuits
including a conductor, said conductors being in
ductively coupled, and means for varying the
control grid, push-pull input and output circuits
therefor having capacity therebetween requiring
coupling between said conductors sufficiently to
produce complete neutralization of said capacity.
3. An amplifier comprising a pair of electron
discharge tubes each including an anode and a
control grid, push-pull input and output circuits
50 therefor having inter-electrode capacity requiring
to be neutralized, a pair of inter-electrode capac
ity neutralizing circuits each connected between
a grid of one tube and an anode of the other
tube, neutralizing capacitance means in said neu
55 tralizing circuits providing approximately the re
to be neutralized, a pair of inter-electrode capac
ity neutralizing circuits each connected between
a grid of one tube and an anode of the other tube,
each of said neutralizing circuits including a con 45
ductor and a condenser, said condenser providing
approximately the reactance required for said
neutralization, said conductors having portions
directly inductively coupled, and means to move
a portion of one of said conductors with respect 50
to the corresponding portion of the other con
ductor su?iciently to produce complete neutral
ization of said capacity.
GEORGE W. FYLER.
55
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