вход по аккаунту


Патент USA US2132830

код для вставки
Oct. V11, 1938.
2,132,830 -
Filed Nov. 20, 1934
Lela/21d DJV'm-éon
Patented Oct. 11, 1938
r j 3 some FREQUENCY AMPLIFIER >7 Y r .
I :;
c“ V'ItelandQDQNorton, Bridgeport, Oonns lassig-norito
.lDictap‘hone :GorporationfNew' York, N. Y.,~a_ .
' " 'corporationof NewIYork -‘
Application November:20,11934?serial Ne. 753,845’ l
e . 11 claim; 1 -(o1‘;"'i'§‘9_-v-iu1)
?rst r"stage. The third and ‘final. stage of the i
This invention relates to f audio-frequency- am
ampli?er, which is transformer coupled to the
pli?ers ‘and more particularly to means for auto
‘secondstage, comprises two‘ electron power tubes
matically controlling-themgain of the ampli?er . -V-—'3—V—~4 of the type-‘45 arranged in push-pull
*whenever'the audio-frequency‘output rises above relation. #The outputrof the push-pull stage is
aiipredetermined voltagelevel.»
transformer coupled to an output circuit con;
' .An'object of the invention is-tov provide in an
tainingrphonographic recording devices. A con
audio-frequency ampli?er ‘simple and effective
ftrol ‘tube V--'5 of the type 56 is coupled to the
‘output circuit in shunt with the recording de
vicesand to vthe grid circuits of the tubes V-—‘l- F10
means for automatically maintaining a'substan
tially constant ' audio-frequency power output.
910 A further object‘ is to provide a stable and" dis»
tortionless-means for effecting wide- >variation of'
the ampli?cation factor at one or-more stages of
‘a multistage? ‘audio-ampli?er in response to
slight changes above a predetermined power-‘level
coil ll. of an audio-frequency transformer‘ 5. The
input circuit 1 may be suitably connected to a
in the ‘output-of a later or ‘?nal stage ‘of said
:V-Z. '. The'power supply for the ampli?er com
prises a power transformer T, a full wave recti
a filter vF and and a voltage divider R.
rA signal input circuit l includes the primary
telephonetransmission line .by 0.1 mfd. blocking
Thermionic ampli?ers have heretofore been‘ "condensers C—I and‘C-—2,rto a microphone'cir
‘used,’ in transmission systems receiving =voice fre
or to any other circuit suitable for impres
quency currents from‘ telephone lines on directly cuit,
from microphones, 'inrlorder to provide ‘sufficient sion of signal voltages at voice frequencies upon
energy for‘ recording the ‘voice frequencies upon
"Tube V—| comprises a plate 'Lfa cathode 8, a
.phonographrecords-w .‘In'lorder that such record , filament
9 for heating the cathode 8,1 a control
be relatively free from; distortion‘ and to ‘ vprevent
blastingw-hen the voice currents rise above ‘a
v:desired amplitude; it has been found- necessary
to control thepower .gainlof the ampli?ersoas to
compensate vfor. variations in ‘the powerwlevel of
the input-.Jcircuit ;. feeding to the ampli?er. »Ii
grid iii, a screen grid H, and a suppressor grid
42. InY-the present arrangement, as it has been
found “desirable to decrease the ampli?cation
factor of tube V—l', the suppressor grid l2 of
that tube is connected to the plate 1. The input
circuit of the tube V--! includesthe secondary
automatic-control means are ‘to .be ‘ employed,~it
t3 "of the transformer -5 which is connected. 30
becomes essential to insure that the rate. of vevari» ‘coil
control grid H] by the conductor M. A.
ation of the ampli?cation factor of thethermi
R-‘l of about 250,000 ohms is .con
onic devices be'rkept well ‘below the'lowest'audio gridresistor
frequencies within the range ‘of. the recording nected across the coil [3. Coil I3 is also con
' nected by means of a resistor R-—l (0.1-meg.)
mechanisms. It is accordingly a further object
of this invention-toprovi'de an automatic volume andlconnection H3 at a point 7vI“! with a line IB,
control havinga time constant relatively large connected by means of a slider contactv 19 with
as compared with the. lowest. audio-‘frequency to aresi'stanceelement R—-l5 (50.0 ohms) of the
‘voltage divider R. The cathode v8 .of the tube
is connected at 21 to a conductor 22, con
Other objects ofvmy inventiontw-illibe pointed ' LV-i-l
nectedat 2.3 to the voltage divider R, which at
out- in the 7 following ‘description taken {in con~
that point is groundedas indicated at 24. The
junction with the drawing; the-:singlei figure of - positive
end of the‘ voltage divider is indicated
which illustrates one embodiment of my invené
at'r25 and the negative end at 26.. The control
grid I0 ‘is normally negatively biased with re
of special design ’connectediinductively to an spect tothe cathode 8 by the voltage drop across
input circuit. and also connected inductively to
4 an output‘ circuit, the latter including suitable the portion of vthe resistance element ‘it-I5 ex
tendingto the right of the slider l9.
.tion as applied to an audio-frequency:v ampli?er
The inventionlaccordingly
recording devices."
I > in
- thelfea
7' -
tures of construction, combinationsof elements,
and‘ arrangements of parts . as will be exempli?ed
mThe ?lament ‘of tube V—-I‘ as well as those
of tubes V:-2 and V--5 are connected, as indi
cated by the conductors .X—X; i130 .a secondary
coil 43 of the power transformer T, the primary
in the system'tos'be-hereinafterdescribed and '28 ~ of which receives energy from a 110420
the scope of the application of which will be
volt,‘ 60-cycle alternating‘ source. A full-wave
recti?er tube E has its anode plates '30, .3! con;
nected: respectively to the extremities of the
55 cated generally by.A will be seen to be of the secondarycoil ~32. of transformer T. ‘The cath
three-stage type- with . a transformer input .to,
the?rst stage, which» comprises a variable mu ode. -33 of recti?er. tubeE is heated by current
secondary coil .34 of the transformer.
electron tube. V—-'l\ of the type; 58.". The second suppliedby
The/midpoint 3.5 of.coil.3.2 is connected to the
stage ‘includes a tubev V-2 ‘of ‘the same type negative sideofthe :voltage divider R by a suit 160.
‘which is resistance‘ coupled tortheoutput. of the
indicated in the following claim.
. _
. Referring to the drawing, thev ampli?er, indi
able conductor 36. The positive side of the volt
age divider is connected by means of a line 31
to the midpoint of the secondary coil 34 through
the choke coils 38 and '39.
These coils in con
junction with the ?lter condensers 40, 4| and
42 serve to smoothout pulsations in the uni-.
Y-Y directly to the terminalsof the secondary
coil 45 of power transformer T. The midpoint
of this coil is connected through va. biasing re
sistor R—~I1 (1,000 ohms) to the negative side
of the recti?er to voltage divider circuit at a
point 19. Thus the amount of negative bias at
directional pulsating current supplied,‘ to the the grids of the push-pull ampli?er‘ tubes is
terminals of the voltage divider by the recti?er ' determined by the resistor R-l‘l. The plates
E. A further secondary coil 45_supplies current
10 to the ?laments of the tubes V—-3--V—4
dicated by the conductors Y-Y.'
as in- .
Returning to the description of the ampli?er,
80 and 8| of ampli?er tubes V—3 and V—-4 are
connected together through the primary coil
82 of the output audio-frequency transformer 83.
The midpoint of this coil is connected through a
the plate 1 of tube V-l ‘is connected through ‘ ‘resistor R-l8 (1,000 ohms) to a point 85 in
the coupling resistor R-3 (0.1 meg.) .to- a con
the positive side of the power recti?er circuit
15 ductor 41 connected at 25 to the positive'end‘ between the choke coils 38 and'39.
of the voltage divider R. The plate circuit re
turn is made through the cathode 8 to the point
23 of the voltage divider. Thus the plate cir
cuit of tube V'—l includes resistance element
R—-l8 (20,000 ohms) of the voltage divider.
The screen grid H of the tube V——I is connected
by means of a conductor 49 and resistor R-4
(25,000 ohms) to- a slider 56 which has movable
The re
sistor R—l8 isjselected to provide a su?iciently
high voltage in the plate to cathode circuit of
the push-pull tubes and since the plate to cath
ode circuits of this stage of the ampli?er do
not include resistances of the voltage divider 20
there is small chance for feed-back from the
output stage to the earlier stages of the ampli
?er. The secondary coil 86 of transformer 83 is
connected by means of an output circuit,'in
eluding a condenser C—8 (0.5 mfd.) in its high 25
may be varied as desired. The screen grid to
potential side, to oneor more phonographic re
cathode circuit is shunted by a condenser C-.—4
cording instruments as indicated at 81 and 88.
(0.5 mid.) and a resistor R—-2 (0.1 meg.) which ’ The low potential side of this output circuit is
serve as a ?lter for that circuit. A similar
grounded-as at 85.
?lter comprises a condenser C—9 (2. mid.)
When the input circuit I receives voice currents 30
shunted across the control grid to cathode cir
from a microphone, telephone circuit, or other
cuit of tube V-—! and the resistor R-l.
wise, each ampli?er stage will increase the en
The plate ‘i of tube V-—l is connected to ergy of such voice currents and if the ampli?er is
the control grid 54 of the tube V--2 through a
properly designed su?icient en'ergy’will be deliv
blocking condenser C-—I2 (0.006 mid). The ered to the recording instruments 81, 88 to en
plate 57 of tube V-—2 is connected through the able them to out sound grooves upon the records 3.5
primary coil 58 of an audio-frequency trans
used in connection therewith. Unfortunately,
former 59 through a suitable resistor _R—9
the power level of the input circuit I may vary,
(75,000 ohms) to the conductor 41. The cath
for example, from +10 to —40 db., rating 0 at
4,0 ode GI of tube V—-2 is connected as at B2 to 0.006 watt. Therefore, it is not possible always 40
conductor 22. The plate to cathode circuit of
to get satisfactory recording results with an am
tube V-2 is, therefore, connected across the
pli?er of this type unless compensation is made
same resistance element of the voltage divider
for such variations in input power level. Such
as the similar circuit of tube V--I. As with
variations are particularly likely to occur where
tube V-—l the suppressor grid 63 is connected to the ampli?er is connected alternately to long
the plate 51. Since the second ampli?er stage and short telephone transmission lines.
is transformer coupled to the push-pull stage
suppose the input circuit power level to be
the tube V.—2 need not have as high an ampli
—40 db. and that there is an input circuit cou
?cation vfactor as tube V—I. It is desirable, pling loss of 20 db. Then, if for satisfactory re
cording results it is desirable to hold the power
power capacity. Hence the screen, grid 64 vis level in the output circuit at +20 db., it follows 50
connected directly to the suppressor grid‘ 63'and thatthe ampli?er must have a maximum power
plate 51. The control grid circuit of tube V-—2 gain of at least 80 db.
T '
includes the resistors R.——_5 (250,000 ohms) and '
But should the energy level of the'input cir
55 R—'6 (.1 meg.) and is connected through the
cuit rise to —20 db. it would follow that the'80 db. 555
conductors l6 and I8 to the slider contact [9
gain of the ampli?er would result in a too high
and the voltage divider. Thus the control grid power level in the output circuit.
biasv for tube V—2 is provided by the voltage
~ From such a'condition there would arise a lack
drop across the same portion‘ of resistance ele
of uniformity in the amplitude of, the recording,
60 ment R—l5 that provides grid bias for tube
causing the records‘to vary greatly in loudness .60
V—l. A condenser C-—'l (0.5 mfd.) provides an
when reproduced; and even in respect to a single
audio-frequency path between transformer pri
record, great differences in loudness'would occur
mary and cathode 6|. A condenser C—5 (0.5
at different points in the record.
,' ' 1
mfd.) provides a by-pass between cathode 6|
has been provided ‘with an automatic volume 65
The ampli?ed audio-frequency voltages on the
control comprising an electron tube V—5 of the
plate 57 are impressed upon the grids 10 and ‘H
type 56. The "cathode 90 of this tube is con
of tubes V—3 and V-—4, the'impressed voltage nected at point 9| to the voltage'divider. The
being derived from the secondary coil 14 of control grid 92 is connected by means of a slider
70 transformer 59. The return circuit for the two contact‘ 93 with the resistance element R’_l2
grids 10 and ‘H is by means of a wire 15 con
(2,000 ohms) of the voltage divider through the
nected to the midpoint of transformer coil 14 grid resistor R-l0 (0.1 meg). The grid 92 is
and leading to the negative side 26 of voltage
also connected by awire 96 through a condenser
divider R. The ?lament cathodes ‘l6 and 11 of C—3 (0.1 mfd.) at a point 98 with the high po
-7 5 these tubes are connected through the lines tential side of the output or load circuit. The
contact with the element R—l6 of the voltage
divider. Thus the potential of the screengrid
plate 99 of tube V-5 is connected to the con
ductor l8 and thus to slider contact i9 and the
voltage divider. A resistor R—ll (0.1 meg.) is
included in the conductor l8 at a point between
its connection with the plate 99 and the slider
IS. The plate circuit of the tube V-—5 thus in
cludes resistor RF—| l, resistance element R—-I3
(7,000 ohms) and the lefthand portion of R-l5,
while the grid to cathode circuit of the said tube
10 includes that portion of the voltage divider re
sistance R—l2 that is disposed between the slider
contact 93 and the point 9 I. It will be seen that
the resistor R—ll is included not only in the
plate circuit of the control tube V—5 but also in
the grid circuits of the variable mu ampli?er
tubes V——l and V--2. This resistance provides the
means for varying the grid bias of the variable
mu tubes in response to variations in the energy
level of the output circuit impressed on the grid
20 of V—-5.
Normally, in operation, the slider contact 93 is
adjusted so as to provide a negative potential on
the grid 92 of the control tube of such value
that the control tube is biased approximately to
cut-off. The biasing of grid 92 by means of the
slider contact 93 is adjusted so that ‘until the
energy of the output circuit exceeds a predeter
mined level a negligible quantity of current will
flow in the plate circuit of the control tube V—5.
so When, however, the said output energy rises
even slightly above its predetermined level the
grid 92 of the control tube will become more
positive and current will flow through the plate
circuit thereof and through the resistance-R-l l.
The voltage drop across the resistance R--H will
cause the control grids l0 and 54 of the variable
mu tubes V-l and V—2 to become more negative
and thus reduce the ampli?cation factors of
these tubes. By proper designing, the control
40 tube may be made to produce great variation in
the ampli?cation factors of the variable mu
tubes in response to very slight increases in the
power level of the output circuit. As soon as the
decreased ampli?cation of the tubes V—l and
V—2 effects suf?cient reduction in the output
level, current of any appreciable value will cease
to ?ow through the resistor R—al I and the grids
of the tubes V—I and V-—2, becoming again more
positive, the ampli?cation factors of those tubes
will increase in value. In this way a substan
tially constant power level may be maintained at
of the series resistance R-—ll and the shunt
capacitance C-I0. By properly determining the
value of capacitance C--l0 in relation to re
sistance R-—ll any desired time constant may be
attained. Practically this is adjusted so that
there will be sufficient delay to prevent a rapid
shift from low to- high ampli?cation and vice
versa between syllables or words of the matter 10
To obtain the best results tubes V-l and V—2
are operated at ground potential. The ground
ing of their cathodes at 24 tends to stabilize the
circuits of these tubes. The grid circuit of the 15
control tube is also grounded through a condens
er C—I3 (4 mid).
Another important feature of the present am
pli?er is the resistor R—'l, which tends to sta—
bilize the grid circuit of the ?rst ampli?er tube 20
It will be seen that there is provided a con
struction of an essentially practical nature in
which the several objects of this invention are
matter herein set forth or shown in the accom
panying drawing is to be interpreted as illus
trative and not in a limiting sense.
I claim:
In an audio-frequency amplifying system of
the type wherein the vacuum tube ampli?er de
rives its operating potentials from a potentiome 35
ter connected across a direct current source of
power, a vacuum tube control circuit deriving its
necessary operating potentials from said poten
tiometer and adapted to cause a grid bias of
said ampli?er to become more negative as the 40
output of said ampli?er increases, comprising,
in combination, a control vacuum tube having a
cathode, anode and grid, a capacitative connec
tion from said grid to said ampli?er at a point
which varies in potential in
audio-frequency output of
other connection from said
resistance to an adjustable
accordance with the
said ampli?er, an
grid through a ?rst
tap on said poten
tiometer at a ?rst point near the negative end
thereof, said ?rst point being effectively ground
ed through a ?rst condenser, a connection from
said potentiometer at a second point interme
the intensity of the voice currents received at
diate its ends to ground and to a cathode of
said ampli?er, a connection from said control
tube cathode to said potentiometer at a third
It should here be noted that the automatic
control of the ampli?cation factors of variable
point intermediate said ?rst and second points,
mu tubes in a plurality of different stages of the
a connection from said control tube anode to a
grid circuit of said ampli?er and through a sec
ond resistance to an adjustable tap at a fourth
ampli?er presents a problem quite different from
that where control is con?ned to a single stage.
60 The maximum amount of ampli?cation allowed
As many possible embodiments may be made
of the above invention without departing from
the scope thereof, it is to be understood that all
the output stage of the ampli?er irrespective of
_'the input stage thereof.
determine the time constant of the control cir
cuit which is substantially equal to the product
point on said potentiometer intermediate said 60
.to the tubes of each stage becomes an important
factor. Since as in the present embodiment of
the invention the grids of the two controlled
tubes are connected to the same control element
65 and receive their normal voltage bias from the
same source, it is highly important that proper
means be employed to prevent feed-back between
the respective grid circuits. This purpose is at
second and third points, a second condenser con
nected between said anode and said second point,
the values of said second resistance and said sec
ond condenser determining the time constant of
operation of said control circuit, and other neces 65
tained herein by shunting a condenser C-lll (1.
across the grid cathode circuits of the
70 mid.)
controlled tubes. This condenser serves also to
second point.
sary operating circuits of said ampli?er deriving
their potentials from said potentiometer at
points between the positive end thereof and said
Без категории
Размер файла
617 Кб
Пожаловаться на содержимое документа