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Патент USA US2096756

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Oct. 26, 1937.
.
E. S. PURINGTON
2,096,756
DYNAMIC MULTIPLIER
Filed June 25, 1935
m l m“
LVVQENTORH
EHison S. Pufing'l'on.
ATTORNEY
‘2,096,756
Patented Oct. 26, 1937
UNITED » STATES '
PATENT OFFICE
2,096,756
DYNAMIC MULTIPLIER
Ellison S. Purington,,Gloucester, Massnassignor
to John Hays Hammond, Jr., Gloucester, Mass.
Application June 25, 1935, Serial No. 28,230
18 Claims. '(Cl. 179-1001)
and for records requiring rapid expansion at low
This invention relates to sound reproducing
systems, and more particularly to an improved
system for automatically expanding or multiply
ing the dynamic range of sound energy. The in
volume.
The invention also provides tone control means '
to discriminate against the higherfrequencies,
5 vention provides more speci?cally for obtaining particularly when the volume control is set for
the desired dynamic expansion or multiplication - high input values. Manual adjusting means may
be included to effect the necessary control for
in a single stage of‘ ampli?cation.
.
.
'
In one embodiment tubes having a plurality of diiierent records. '
control elements are used to produce the desired
10 dynamic range in a single stage of ampli?cation
without critical adjustments. The tubes may be
of the triple grid type in which case the dynamic
. control is preferably applied to the ?rst or con
trol grid and the'third or suppressor grid, the
15 plate voltage and second or screen grid’ voltage
being ?xed at their normal rated values with
respect to the cathodes. In the absence of sig
nals, the control grid may be biased to, for ex
ample, about —‘7 to —10 volts, and thesuppressor
20 grid may have a potential of from -,-30 to —40
volts. With increase of signal the negative bias
- on these grids is decreased as an increasing func
tion of the signal strength up to a predetermined
maximum bythe action of a control circuit. vThe
25 control circuit may comprise an auxiliary ampli
?er tube of the duplex-diode triode type (com
mercial type 55, for example) feeding a network
including a pair of recti?ers and resistances so as
to build up a voltage drop across the resistances
proportional to the signal strength. The resist ances are connected in circuit respectively with
the control grids and the ‘suppressor grids of the
main ampli?er so that the voltage drop therein
opposes the normal negative‘bias of said grids.
The diodes of the auxiliary ampli?ef tube may be
used to limit the voltage drop across the resist
ances to a predetermined value so as to prevent
the biasing potential on the control .and sup
pressor grids from dropping to a value such that
40 distortion would result.
'
By applying control to the two sets of grids it
is possible to obtain sufficient control in one stage
of ampli?cation without necessitating critical ad
The invention also consists in the various new
and original features of construction and com 10
binations of parts hereinafter set forth and
claimed.
Although the'novel features which are believed
to be characteristic of this invention will be par
ticularly pointed out in the claims appended here 15
to, the invention itself, as to its objects and ad
vantages, the mode of its operation and the man- ‘
ner of its organization may be better understood
by referring to the following description taken in \
connection with the accompanying drawing form-' 20
ing. a part thereof, in which:
The ?gure‘illustrates diagrammatically the sys
tem as applied to the reproduction of sound from
the sound record of a talking moving picture pro
jector and phonograph.
'
.
'
In the following description and in the claims,
various parts will be identi?ed by speci?c names
for convenience, but they are intended to be as
generic in their application to similar parts as the
art will permit._
Referring to the acompanying drawing more in ‘
detail, a phonograph pick up “I is shown which
is connected to two contacts ofa double-pole.
double-throw switch H, the other contacts of
which are connected through a transformer I2 35
to a photoelectric cell 13.
Light from a lamp- “! '
is focused, by means of a lens l5, through an
aperture HS in an aperture plate ll, upon the
sound record of a moving photographic ?lm 18.
The light which passesthrough this ?lm then im
pinges on .the photoelectric cell l3.
_
The blades of the switch II are! connected
through a transformer 20 to the input circuit of
> justments of the initial bias settings. By using l a space discharge ampli?er 2|. Connected across
this input circuit is a tone control ?lter compris 45
45 for the main ampli?er a type of triple grid tube
with remote cut off on-the control grid (com
' mercial type 58, for example)
the control on
ing parallel branches, one containing‘a resist
ance 22 and a condenser 23 in series, and the
this grid will be smooth and uniform, determining other containing a resistance 25. This tone- con,-v
trol ?lter is a compensating device adapted to
the dynamic range of the ampli?er, while the con‘
trolon the suppressor grid may be made abrupt . compensate for the undercutting of the bass tones 50
so as to suppress noise, for example, in periods-of in a sound record. The ?lter emphasizes the bass
small or zero signal strength. However, the
abrupt- cut off type of triple grid tube (com
mercial type-57) 'may be also used to advantage
in some instances, especially for. sound on ?lm
tones by loading the transformer 20 more for high
frequencies than forlow frequencies. It is to- be
noted that this ?lter can be omitted provided a
compensated pickup or transformer is employed. 55
2
2,096,756
‘It is useful, however, when a transformer or pick
up having ?at characteristics is employed and its
value, will depend upon the transmission characteristics of the transformer or pick-up and the
characteristics of the record which is to be com
pensated. The output circuit; of the ampli?er 2|
tentiometer 58. These elements may be adjusted _
to effect the desired frequency transmission
characteristics or, in the event that the trans
former 43 isdesigned to produce the desired ?
delity, these elements may be omitted.
.
The tubes of the power‘ ampli?er 44 ar -
includes a scratch ?lter 26 and two potentiom vpreferably of the triple grid vtype. having a
cathode 5|, control grids 52, screen grids 53,
eters 21 and 28 in series. The scratch ?lter 23 is
used to cut out excessive high tones, such for ex.-_ and suppressor grids 54. The control grids 52
may be connected to the secondary of the trans
10 ample as all tones above a frequency of 6000 cycles
and may be of any well known design adapted to
former 43.
produce the desired characteristics. The ampli-»
grids 54 may be grounded and the screen grids
?er 2| is supplied with plate power from a tap 29
on a battery assembly 38. The potentiometer
15. 21 is connected to a tone circuit 24 comprising a
The cathodes‘ 5| and suppressor
53 may be connected to, the tap 29 on the'bat
tery assembly 38;
A tone '?lter comprising‘
parallel branches, one containing a resistance 58 15
high pass ?lter network adapted to shunt more and a condenser 59 in series, and the other ‘con
of the high frequencies than the low frequencies, taining two condensers 68, may be connected
the effect being determined by the podtion of the across the output circuit of the power ampli?er
movable contact of the potentiometer-11. When 44. This tone ?lter ‘is designed to dampen out
20 this contact is raised (as viewed in the drawing) ' resonant frequencies which are occasionedv by
a greater proportion of the higher frequencies are the mechanical vibrating elements. The char
shunted and vice versa. The potentiometers 31 ‘ ,acteristics depend upon the resonance character
and 28 provide a constant impedance output for istics of the speaker. Compensation for the me
the ampli?er 2| ‘while permitting adjustment of chanical resonance of the speaker may also be
25 the energy fed to the next stage of ampli?cation ' effected in other well knownways in which case
the tone ?lter will be modi?ed accordinglyor
and to the tone circuit.
_
The potentiometer 28 is connected through a may be omitted in certain instances. The ?eld
transformer 3| to the input circuit of a push-pull coil 8| of the loud speaker 46 may be connected
ampli?er 32 comprising two tubes 33 having a between the tap 29 and a tap 82 on the battery
assembly 38.
>
'
30 plurality of control elements, such for example
as triple grid tubes of the type known com
Connected across the output circuit of the
mercially as 57 or 58, and having cathode 34, ampli?er 2| by a coupling ‘resistance 85 is a
control grids 35, screen grids 36 and suppressor . branch ampli?er recti?er system including a
grids 31. The secondary of the transformer 3| duplex-diode triode tube 88, which may be of
may be connected to the control grids 33 and commercial type 55, for example, andmay have
the cathodes 34 may be grounded. The screen
a cathode 81, a grid 88, an anode 89 and a pair of
grids 36 may be connected to a tap 38 on a re
diodes ‘I8 and 1|. The grid bias is applied to the
sistor 39, which is connected between the tap , tube 86 from a tap‘ ‘I2 on a. control resistor as
29 on the battery assembly 38 and ground. ‘ '
sembly 13, which is connected between the nega
The output circuit of the ampli?er 32 is con
tive terminal of the battery 38 and ground. The
40
nected'through a transformer 43 to the input cathode potential of the tube 83 is determined
circuit of a push-pull power ampli?er 44, the by a tap 14 on a second -_resistor assembly 15,
output circuit of which is connected through a which is in parallel with the resistor assembly
transformer“ to the, moving coil of a loud _ 13 and is designed to carry heavy currents. ‘The
plate 69 of the tube 68 may be connected through
‘speaker 46.
.
'
A resistance 41 may be connected across the
the primary of a transformer 18 and a resistance
primary of the transformer 43 to maintain the 98 to the tap 29 of the battery 38.
frequency characteristics substantially inde
The control grids 35 of the tubes 33 are con
pendent of the gain ratio characteristics. This nected through a resistance 88 and a resistance
resistance 41 has a value such that the combined
8|, to an adjustable contact 82 on the resistor
impedance of this resistance and the internal assembly 13. The suppressor grids 31 are con
output impedance of the tubes 33 in parallel nected through a resistance 83 to an adjustable
approximates the impedance for which the contact 84 of the resistor assembly 13. The re
transformer 43- is designed to effect uniform sistance 8|, being-in the output circuit of the
tube 86, should have a value somewhat greater
55 transmission on all frequencies within the de
sired range. If the transformer 43 is designed to 7' than the internal output impedance of said tube
operate across an input impedance correspond
in order to operate most effectively therewith
ing to the internal outputimpedance of the and may be varied in accordance with the design
tubes 33 this resistance 41 can be omitted. of the tube 66 to‘ produce the most effective
to The tubes 33 may be supplied with plate power ' results. The resistance 88 is high as compared
from the tap 29 on the battery assembly 38. to the resistance 8| so that the parallel circuit
A ?lter network comprising parallel branches, including the resistance 88 and the condenser I88
one containing a resistance 48 and the other con‘
will not interfere with the operation of the re
taining a condenser 49 and potentiometer 58 in' sistance 8|. It should not be sufficiently high,
series, may be connected across the secondary of however, to introduce excessive resistance in the
the transformer 43 for ‘tone control purposes.
grid return circuit in which it is connected. The
The resistance 48 is of a value adapted to cor
resistance 83 has a valueaof the order of the
root for the lack of ?delity of the transformer rated secondary output impedance of the trans
43 and may be omitted provided the transformer former 18 across which it is connected through
,
70 is designed to operate satisfactorily without the the recti?er tube 96 to be described.
The output circuit of the auxiliary ampli?er
same. The condenser 49 and potentiometer 58
are used for tone control purposes and provide a tube 86 comprises parallel branches, one includ
partial shunt for the high frequencies, the ing a stopping condenser 88,'a resistance 89 and
characteristics of which depend upon the value the resistance 8|, the other including the pri
75 of the condenser 49 and the setting of the po- , mary of the transformer". The condenser 88
20
25
30
40
so
60
‘
65
70
3
2,096,756,v
is used as a blocking condenser.
The resistance
7 89 together with the resistance 80 and the con
denser 88 determines in part. the frequency re
sponse characteristics of the control circuit.
A recti?er 9| having acathode 92 and anode
93 is connected. across the resistance 8| in such
manner that current passes through the resist
ance 8| only in the direction of the arrow,
whereby the potential drop in the resistance 8|
10 opposes the. normal negative bias on the grids
35 derived from the tap 82; The recti?er 9| may
comprise a three element tube having a grid 94
connected to the anode 93. J ‘
i
.
The secondarycircuit. of the‘ transformer 16
15 may include a recti?er 96 and the resistance 83
in series, the recti?er 96 being adapted'to pass
current through the resistance 83 only in the di
more resistance is put in parallel with the tone
circuit 24 thus causing more and more of the
high frequency tones to be shunted and. decreas
ing the proportion of high frequency supplied to
the ampli?er 32.
-
'
Energy is fed from the potentiometer 28 to the
input circuit of the push-pull ampli?er 32 the
amount being determined by the setting of the
potentiometer 28. This energy is ampli?ed‘ by
the ampli?er 32 and is fed through the trans 10
former 43 to the push-pull power ampli?er 4,4
where it is‘ further ampli?ed. The output of the
ampli?er 44 is then fed through the transformer
45 to the loud speaker .46 where it is reproduced
15
as speech or music in a well known manner.
Some of the energy ‘from the output circuit of
the ampli?er 2| passes to the branch ampli?er
rection of the arrow so' that the voltage drop in _ recti?er system where it is ampli?ed by the auxi
" said resistance opposes'the normal negative grid iliary ampli?er 66 and is fed to the resistance 8|
and to the transformer ‘16. A portion of'the 20
20 bias applied to the suppressor grids 31 from the
contact 84. -The recti?er 96 may also comprise
a three element tube having a grid 91 connected
to its anode 98.
'
The diodes 10 and 1| of the ampli?ertube 66
energy thus passes through the stoppage con
denser 88, resistances 89 and 8| and recti?er 9|, '
causing a ?ow of unidirectional pulsating cur
rent, through the resistance 8| in the direction
of the arrow, thereby building up a pulsating po 25
25 may be used to limit the voltage drop in the re
sistances 8| and 83 respectively. For this pur ' tential di?’erence across this resistance, which
pose they are connected to the positive ends of ?uctuates in accordance with the envelope of
said resistances. The diode ‘10, for example, may the signal strength impressed on resistor .65, and
opposes the negative potential which is normally
be connected through the resistance 80 to the imposed upon the'control grids of the ampli?er 30
30 positive end of the resistance 8|, and. the diode
1| may be connected to the positive end of the‘ 32 from the contact 82 of the resistor assembly
resistance 83. When the potential dropacross 13. The potential thus produced across the re-'
said resistances becomes such that the diodes I sistance 8| automatically increases the gain ra
become positive with respect to the cathode 61 tio of the. ampli?er 32 with increase'of signal 35
and vice versa. The rate of increase or
as of the tube 66 space current will ?ow between - strength
the cathode‘ and the diodes and further increase decrease of the gain ratio or the time constant
of the circuit is determined by the value of the
in potential drop across said resistances is pre
condenser I00 and resistance 80- which may be
vented. Condensers I00 and |0| may be con
nected between the diodes 10 and 1| and ground selected in accordance with the effect desired.
The potential drop across the resistance 8| is 40
40 to control the timing of the control circuit. The
limited
by theaction of the diode 10, which pre
condenser. I00, in connection with the resistance vents this
potential from increasing beyond a
80, controls the time constant of the control cir- '
cuit and is chosen to produce the desired effect
of the crescendo and decrescendo of the repro-v
45 duced signal. The condenser |0| serves a simi
lar function in controlling the time constant of
the suppressor grid. The condensers I00 and
|0| may be designed to cause the signal grid and
suppressor grid to operate at the same time con
50 stant although in certain instances it may be v
desirable to select these elements so as to cause
the signal and suppressor grids to operate at dif
ferent time constants depending upon the effect
desired.
,
A triple pole double throw switch I02 is ‘pro
vided for controlling the dynamic operation of
the circuit. When this switch is thrown up the
two diodes 10 and 1| of the tube 68 are connected
together andv to a tap I03 on the resistor as
60 sembly 13. When the‘switch I02 is open, these
electrodes are independent of each other, and
when the switch is thrown down the resistance
89 is short circuited. The cathodes of the vari
- ous tubes may be heated in any well known man
65 ner, as by separate heaters supplied from a con
venient source of current, not shown.
_
In the operation‘ of ‘the form of the invention
shown in the accompanying ?gure, the energy re
ceived by the transformer 20 passes to the ampli
70 ?er 2| where it is ampli?ed and fed through the
?lter circuit 26, which eliminates the extremely
high frequencies, to the potentiometers 21 and
28. vWhen the arm of the potentiometer 21 is in
its lowest position the tone circuit 24 is short
75 circuited. As' this arm is ,moved up more and
predetermined value, dependent upon the poten
tial of the cathode 61 as determined by the posi
tion of the tap 14 on the resistor assembly 15. 45
Any increase of potential above this amount
will cause a. flow of current from ‘the diode 10 to
the cathode 61, thus limiting the potential im- ‘
pressed on the grids 35 of the ampli?er tubes 33
to a value within the range of ef?cient operation 50
thereof.
‘
,
The energy from the ampli?er 66 which passes
through the transformer 16 is recti?ed by the
recti?er 96 and ?ows through the resistance 83
in the direction of the arrow. This produces a, 55
potential difference across’ the resistance 83
which opposes the negative bias, normally im
pressed on the suppressor grids 31 of the ampli
?er 32 from the contact 84 on theresistor assem
'bly 13. ‘In this way increase, of signal produces 60
a further increase in gainratio of the ampli?er
32. The time constant of this increase in gain
ratio is ‘determined by the value of condenser |0|
and the associated. circuits which may be selected
to properly accentuate the change in gain ratio 65
produced by the control grid. '
The positive potential produced by the flow of I
current through the resistance 83 is limited by. the
action of the diode 1|, which prevents this poten
tial from ' increasing beyond a predetermined
O
Value,-dependent uponthe potential of the oath
ode 61 of the tube 66.
In this way the potential ‘
impressed upon the suppressor grids of the am- -
pli?er 32 is also limited by the action of the tube
66.
4
‘
75
2,096,756
With the switch [02 in the open position, as
just described, expansion of a gradual nature is
produced for high quality records, etc. If more
abrupt expansion is desired, as for dance music
and speech, the switch 102 is thrown down, thus
short circuiting the resistance 89 which permits
a greater amount of energy to be impressed upon
the resistance 8|, thus increasing the speed of ,its
action upon the ampli?er 32.v
-
10' If non-dynamic or normal operation of the cir
cuit is desired, the switch “I2 is thrown up, thus
connecting bothvthe input circuit of the ampli-_
_?er 32 and the suppressor grids to the tap I03
on the resistor assembly 15 which eliminates the
15 action ‘of the resistances 8| and 83 and allows
the circuit to operate substantially as a normal
'ampli?ea
.
I
'
It will be understood that there may be inter
linking of controls, as for example, control of
20 the low or initial bias settings of contacts 82 and
-84 simultaneously with volume control of _poten
tiometers 21 and 28 so as to provideless expan
sion when the potentiometer is set for less volume
and vice-versa.
25
-
It will be noted that the above system pro
vides for dynamic control on the control grid, and
alsoon an additional control element of the tube.
In this way, a great expansion is »made possible
in a single stage of ampli?cation.
The use ‘of a '
30 duplex-diode triode ampli?er tube permits the
.
sary to an understanding of the present invention‘
and that the circuit may include the usual sources
of potential, controls, etc.
_
Although only a few of the various‘ _forms in
which this invention may be embodied have been
shown herein, it'isto be understood that the in
vention is not limited to any speci?c construc
tion, but might be embodied in various forms
without departing from the spirit of the inven
tion or the scope of the appended claims.
10
What is claimed is:
‘
1. In a system for reproducing sound, an am
pli?er comprising a_ space discharge tube hav
ing a plurality of control electrodes connected to
receive a biasing potential for controlling the 15
transmission characteristics of the tube a source
of audio frequency sound energy, means to supply
said audio frequency sound energy to one of said
control electrodes, and means to vary the bias
ing potential on said last control electrode and 20
also on an additional control electrode in accord
ance with the envelope of the sound energy so
that both control electrodes operate to vary the
gain ratio of the tube as an increasing function
of the sound energy whereby the additive control 25
effect of both control electrodes is utilized for ex
panding the dynamic range of the reproduced
signal.
2. In a system for reproducing sound, an am-l
pli?er comprising a pair of space discharge tubes 30
connected in push-pull relationship, said tubes
each having a plurality of control electrodes the
limiting action to be obtained with a'minimum
number of tubes. Obviously, this could be done in
the ampli?er 2| instead of in the ampli?er 66, if ' corresponding control electrodes of the two tubes
being connected by a common return to a source
desired.
35 -The rectifying system embodies one possible of biasing potential'for controlling the trans
arrangement .in which two types of recti?cation mission characteristics of the tube, a source of
are utilized; one in ‘which the load is in series
with the recti?er and the other in which‘ the out
audio frequency sound energy, means to supply
said audio frequency sound energy to one of said
put voltage is developed in a resistor across the ‘ control electrodes of each tube and means to vary >
the biasing potential on said last control electrode 40
'The tone. control circuits used in connection and also on an additional control electrode of
with the various ampli?ers and the constant im~ each tube, in accordance with the envelope of the
pedance output of the ampli?er 2| prevent tone sound energy so that both control electrodes
distortion in the system. It is to be understood operatev to vary the gainv ratio of the tube as an
increasing function of the sound energy whereby 45
45 that the various ?lters referred to above may be
selected in accordance with standard ?lter de » the additive control effect of both control elec
sign and are determined by the characteristics of trodes is utilized for expanding the .dynamic
range of the reproduced signal.
_
the cooperating elements of the circuit. For ex
3. In a. system for reproducing sound, an ampli
ample, the ?lter requirements depend upon the
?er comprising a space discharge tube having a 50
50 mechanical and electrical characteristics‘of the
record, the pickup and the reproducing device plurality of control electrodes connected to re
ceive a biasing potential for controlling the trans
and upon the transmission characteristics of the
mission characteristics of the tube, a source of
various tran'sformersand intertube coupling de
, vices.
It is to be understood that these devices audio frequency sound energy, means to supply
55 are shown diagrammatically in their simplest
said _audio frequency sound energy to one of
form and that they may be constructed in ac
said control electrodes, means to vary the biasing
cordance with the usual‘ practice. The value of potential on said last control electrode and also
the various resistances and impedances which on an additional control electrode, in accordance
are used for control purposes will depend upon with the envelope of the sound energy so that
the characteristics of the particular ‘tubes with both control electrodes operate to vary the gain
which they are to operate and will be determined -ratio of the tube as an increasing function of
the 'sound'energy whereby the additive control
in accordance with the known internal output im
pedance of such tubes so as to produce the most
e?ect of both control electrodes is utilized _for ex
panding the dynamic range of the reproduced
desirable results. The timing of the control-cir
65 cuits is a matter of choice depending upon the
signal, and means to limit the change in biasing 65
results desired and thecharacteristics of theme
potential on each control electrode so as to pre
0rd. Expansion of a gradual nature maybe‘ re
vent signal distortion due to overloading.
quired for high quality records, for example,
4. In a system for reproducing sound, an ampli
whereas a more’ rapid expansion may be desired fier comprising a space discharge tube having a
70 for dance music or for records‘ having extreme plurality of control electrodes connected to re 70
volume ranges such as certain symphony records.
ceive a biasing potential for controllingv the trans
40
recti?er.
'
l
.
. A wide range of adjustment is possible by varying
mission characteristics of the tube, a source of
the different elements in the manner set forth
above. It is also to be understood that only so
audio frequency sound energy, means to supply
said audio frequency sound energy to one of said
75 ‘much of the circuit has been set forth as is neces
control electrodes, a control circuit including an 75
5
2,096,766
ampli?er, a resistor, means for
rectional current through said
tional to the output energy of
?er whereby a potential drop is
across, and means applying said
passing a unidi
resistor propor-_
said last ampli
change in biasing potential to a predetermined‘
value for preventing overloading of the tube.
9. In a system for reproducing sound, an ampli
developed there
potential drop to
?er having a control electrode connected to re
‘ oppose the normal biasing potential on a plurality
of said control electrodes in said tube whereby
the additive effect of both control electrodes is
utilized to cause the gain ratio of said tube to
10 vary as an increasing function of the sound en
ery for expanding thehdynamic range of the re
produced signal;
'
,y ‘ v
I‘
I
5. In a system for reproducing sound, an ampli
?er comprising a space discharge tubehaving a
ceive audio frequency signal energy, a control cir
cuit fed by the signal energy and connected to
control the biasing potential on said control elec
trode, said control circuit including-an ampli?er
tube of the type having‘ a limiting electrode .
therein and means connecting said limiting elec 10
trode to limit the control exercised by said con- '
' trol circuit on said biasing potential.
10. In‘ a' system for reproducingsound, an audio
ampli?er including a variable impedance device,
'15 plurality ,of control electrodes, a source of audio - a source of audio frequency sound energy, a con
frequency sound energy, means to supply said
audio frequency sound energy to one of said con-'
trol electrodes, a control circuit including an
ampli?er, a pair of resistances, means for passing
20 a unidirectional current through said resistances
proportional to the output energy of said last
ampli?er whereby a potential drop is developed -
thereacross, and means applying said potential
drop to oppose the normal biasing potential on
25 a plurality of said control electrodes in each tube
whereby the gain ratio of said ?rst ampli?er
varies as an increasing function of said sound
energy, and means to limit the potential drop,
across said resistances to a value such that dis
30 tortion of the ampli?ed signal is prevented.
trol circuit adapted to vary the impedance of
said device as a function of the envelope of said <
sound energy, said control circuit including a
duplex ampli?er-limiter tube having a limiter
electrode connected to limit the impedance varia
tions produced by said control circuit.
20
11'. In a system for reproducing sound, an am- ,
pli?er comprising -a multiple grid tube, a source
of audio frequency sound energy, means to im
press said audio frequency sound energyon one 25
of said grids, a control circuit also fed by said
audio frequency sound energy and adapted to V2 ry
the bias on a plurality of said grids according
to the'average signal strength, said control cir
cuit including a duplex-diode-triode tube, the 30
6, In a system for reproducing sound, an ampli ' ,triode electrodes being connected to amplify the
?er comprising a space discharge tube having a energy in the control circuit, the diode electrodes
plurality of control electrodes, a source of-audio being connected to limit the variation of bias
frequency sound energy, means to supply said produced by the control circuit.
12. In a system of reproducing sound, a space 35
35 sound energy to one of said control electrodes,
a control circuit including anampli?er tube of discharge ampli?er having two controlelectrodes
the duplex-diode-triode type, means vsupplying
energy proportionalto said sound energy to said
in one tube connected to- a source of biasing po- _
tential, a control circuit. forcontrolling the gain _
ratio of said ampli?er, means for applying an
audio frequency input signal to one of said elec 40
?er means associated with said impedance means , trodes and to said control circuit,.said control
triode, impedance means connected to receive en
40 ergy from the output circuit of said triode, recti
to produce a potential drop thereacross propor
circuit being adapted to vary the biasing poten
tional to the average sound energy. means‘ tial to both of said control electrodes proportional
whereby said potential drop opposes the normal to said input signal so that both control elec
45 bias on a plurality of said control electrodes, and "trodes operate to vary the gain ratio of said
a limiter circuit including said diodes to limit ampli?er proportionally to ,the average value of
the change in said bias.v
'
_
'7. ‘A system for reproducing sound comprising
a source of audio frequency sound energy, an am
pli?er comprising a space discharge tube having
a control grid and a suppressorhgrid, means sup
plying said audio frequency sound energy to said
control grid, means ‘to apply a biasing potential
to both of said grids and means to vary said
55 biasing potential as a function of the envelope of
said sound energy so that both the control grid
and the suppressor grid operate to increase the
gain ratio ‘of the tube with an increase in sound
energy whereby the additive control effect of both
grids is utilized for expanding the dynamic range
of the reproduced signal.
the input signal whereby the additive control
e?‘ect'of both control electrodes is utilized for
expanding the dynamic range of the reproduced
signal.
,
,
50
~
13. A system for reproducing sound compris
inga space discharge ampli?er having a plu- »
rality of control electrodes for controlling, the
gain ratio thereof, a source of audio frequency
sound energy, a control’ circuit for varying the 55
biasing potential on both of said electrodes for
increasing the gain ratio of the ampli?er as
an increasing function of said sound, energy,
a source of audio frequency sound energy, an
means for applying said audio frequency sound
energy to one of said electrodes and to said 60
control circuit and means associated with said
control circuit for limiting its action on said
control circuit so that overloading of the am
ampli?er comprising a space discharge tube hav
pli?er is prevented,
8. A system for reproducing sound comprising
ing a control grid and a suppressor grid, means
supplying said audio frequency sound energy to
said control grid, means to apply a biasing po
tential to both of said grids, means to vary'said
biasing, potential as a function of the envelope of
70 said sound energy so that both the control grid
and the suppressor grid operate to increase the
gain ratio of the tube with an increase in sound
energy whereby the additive control effect of both
grids is utilized for expanding the dynamic range
75 ofithe' reproduced signal, and means to limit the
.
' ‘
14. A system for reproducing sound ‘compris 65
ing a space discharge ampli?er having‘ a plu
rality’ of control electrodes for controlling the
gain ratio thereof, a control circuit for varying
said gain ratio comprising a second ampli?er, ‘a
resistor connected in the output-circuit of, said 70
ampli?er and means controlled by said resistor
for varying the biasing potentials on-the control
electrodes of said'i?rst ampli?er in accordance
with the average value of the input signal where
by the additive control ,effect of both control 75
,6"
2,098,756
electrodes is utilized for expanding the dynamic
'17. In a system for reproducing sound com
range of the reproduced signal.
15. A system for reproducing sound compris
ing a single stage space discharge ampli?er hav
ing a plurality of control electrodes i'orcontrol
ling the gain ratio thereof, a control cir t for
varying said gain ratio comprising a second am
pli?er, a network including a resistor and recti
?er connected in the output circuit of said second
prising a single stage space discharge ampli?er
having av plurality of control electrodes for con
trolling the gain ratio thereof, a control circuit
having "an impedance, means for passing a
current throughsaid impedance proportional‘ to
the average value of the input signal and means
responsive to the voltage drop in said impedance .
for varying. the biasing potentials applied to
10 ampli?er and means controlled by said network ' the control electrodes oi said ampli?er whereby 10
the additive control e?'ect of both control elec
trodes is utilized for expanding the dynamic
range or the reproduced signal,v and means for
limiting said action when loud signals are ap
plied so that overloading is prevented.
15,
18. In the operation of an ampli?er circuit of
the type including a space discharge tube having
16. In a system for reproducing sound com
prising a single ‘stage space discharge ampli?er a plurality of grid elements one oi’ which is sup
plied with audio frequency variations and having
having a plurality of control electrodes for con
means for establishing di?‘erent biasing poten 20
20 trolling the gain'ratio thereof, a control circuit
having an impedance and means 'for passing a‘ tials upon the several elements, the method of
for varying the potentials on the control elec
trodes of said single stage ampli?er in accord
ance with the average value of the input signal
whereby the additive control e?ect 01' both con
15 trol electrodes is utilized for expanding the dy
namic range oi’ the reproduced signal.
current through said impedance proportional to
the average value oi‘ the input signal and means
25
responsive to the voltage drop in said impedance
for varying the biasing potentials applied to
the control electrodes of said ampli?er whereby
the additive control effect of both control elec
trodes is‘ utilized for expanding the dynamic
range of the reproduced signal.
-
controlling the ampli?cation which comprises
simultaneously varying the biasing potentials of
at least two of ‘said elements as an-increasing
function of the strength of the 'signalsapplied
to the input circuit 01' the'ampli?er.
ELLISON s.‘ RURINGTCN.
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