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Патент USA US2048738

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`Iuly 28, 1936.
P. O. FARNHAM
2,048,738 ,
DETECTOR CIRCUIT
Filed Oct. 14, 1931
PAUL o. FA '
BY fg
.
.
HAM
,Lav/“W
ATTORNEY
Patented July 28, [email protected]
¿48,738A
2,048,738
DETECTOR CIRCUIT
Paul 0. Farnham, Boonton, N. J., assignor to
Radio Corporation of America, a corporation of
Delaware
Application October 14, 1931, Serial No. 568,674
22 Claims. (Cl. Z50-27)
My present invention relates to detector cir
cuits, and more particularly to a- combined am
plifying detector and diode rectifier circuit espe
cially adapted for use in connection with radio
receivers employing automatic gain control.
It has been recognized in the past that one of
the cold electrodes of a detector tube could be
employed in conjunction with the electron emis
sion electrode to provide a diode rectifier which
could be employed for automatic gain control of
the radio frequency amplifier tubes of a radio
receiver. ' It has been well understood in the
prior art that detector circuits could be arranged
to handle large amounts of radio frequency
power, and accordingly produce large audio fre
quency outputs, by employing a type of detection
known as grid bias detection, or anode rectifica
tion, as opposed to the well known type of grid
leak detection. Such a. detector circuit has been
termed a “power detector” stage, Vand has usually
' been so designed as to require only a single Stage
-of audio frequency ampliñcation for energizing
a loud speaker of a radio receiver.
This invention provides a circuit arrangement
which consists essentially of the combination of
a triode power detector and a diode rectifier
within the same vacuum tube. A carrier fre
quency input obtained from a carrier frequency
amplifier is applied to these two units in parallel.
The useful output of the triode power detector
is obtained as a voltage of the modulation fre
quency appearing across an audio frequency im
pedance connected in the circuit between screen
grid and cathode. This audio voltage may then
be further amplified up to the speaker. The use
ful output of the diode rectifier is obtained as a
direct current potential drop across a resistor
connected in the circuit between anode and cath
40.
ode. This potential drop is then used to control
automatically the gain of the carrier frequency
amplifier by increasing its control grid bias in
the well known manner.
Accordingly, it may be stated that it is one of
the main objects of my present invention to pro
vide a circuit for detecting high frequency en
ergy, which circuit includes an electron discharge
tube provided with an electron emission elec
trode, a control grid, an anode Vand a screen
grid, the circuit being so arranged that the cath
ode,l control grid and screen grid cooperate to
function as a triode detector circuit operating on
the anode rectification principle, while the anode
of the said tube functions with the electron
55. emission electrode as a diode rectifier to auto
matically control the gain of preceding high fre
quency amplifier stages.
_
Another important object of the present in
vention is to provide a detector circuit, in a radio
receiver, utilizing a screen grid tube, which de
tector circuit is arranged to function as a power n
detector, and simultaneously therewith, whose
output circuit includes a device, cooperating with
the cathode of the tube and at least one of the
cold electrodes of the tube, to control the gain
of the radio frequency amplifier stages of the
receiver.
Still another objectV of the present invention
is to provide a `detector circuit employing a screen
grid tube wherein the screen grid is maintained
at a higher direct current potential than the
anode of the tube, and the control grid is main
tained at a lower radio frequency potential than
the said anode, the cathode and anode of the
tube being utilized to function as a diode recti
fier in an automatic gain control system.
20
Still another object of the present invention is
to provide in a radio receiver a detector circuit
utilizing a screen grid tube, means for coupling
the output of the tube to a low frequency ampli
fier, the circuit being arranged to rectify high
frequency energy by anode rectification whereby
the detector circuit functions as a power detector.
And still other objects of the present invention
are to improve generally the simplicity and effi
ciency of radio receivers employing -automatic 30
gain control circuits, and to especially provide a
detector circuit in such -a receiver which is not
only reliable in operation, but is capable of -han
dling large amounts of radio frequency power.
The novel features which I believe to be char
acteristic of my invention are set forth in par
ticularity in the appended claims, the invention
itself, however, as to both its organization and
method of operation will best be understood by
reference to the following description taken in 40
connection with the drawing in which I have in
dicated diagrammatically one circuit arrange
ment whereby my invention may be carried into
effect.
Referring to the accompanying drawing there 45
is shown a high frequency receiving system, as
for exampleV a radio receiver, in conventional
manner. At A there is represented a multi-stage
radio frequency amplifier, it being clearly under
stood that the representation designates any am 50
plifier well known to those skilled in the art, and
which customarily employs a plurality of tuned
radio frequency amplifier stages, each stage utiliz
ing an electron discharge tube.4
The source of >55 ~
2
2,048,738
radio frequency energy, usually coupled to the
input of the amplifier A, is not shown, and it
will be understood that the source may be, for
example, an antenna system. The output of the
amplifier A is coupled, as at M, to the input elec
variable condenser C may be arranged for simul
taneous and similar operation with the variable
condensers usually employed in the tuned stages
of the radio frequency amplifier A.
It has been stated, heretofore, that one of the 5
trodes of a detector tube I.
The latter is preferably an electron discharge
tube of the well known “224” type. That is to say,
the tube embodies a cathode for emitting elec
10 trons, a control grid, an anode, and an auxiliary
screen grid. The detector circuit, as has been
heretofore pointed out, is arranged in a manner
prime objects of the present invention is to pro
vide a detector stage not only capable of func--
not known to those skilled in the prior art, the
arrangement being such that the detector stage
15 is capable of handling large amounts of radio fre
quency power, and simultaneously able to control
the gain of the amplifier A in an automatic man
in such a manner that the anode 2 functions in
conjunction with the cathode 3 as a diode rec
ner.
To secure the aforementioned novel results and
functions, the tunable oscillatory circuit, compris
ing the coilv L and the variable condenser C, is
connected between the anode Zand the cathode
3 of the tube I. The anode 2 is connected to the
high potential side of the condenser C through a
fixed capacity 4 having a high impedance for the
modulation frequency,and having an impedance
for the carrier frequency low compared to the
anode-cathode impedance of the tube, while the
cathode 3 is connected to the low potential side
30 , of the condenser C vthrough the Vbiasing resistor
5, which has connected in shunt therewith the
fixed by-pass capacity 6. Asis well known to
those skilled in the art the resistor 5 and con
denser 6 provideV an arrangement for biasing the
control grid 'I of the detector tube.
The control grid 'I is preferably connected to a
point on the coil L of a lower potential than the
point to which the anode 2 is connected, and for
purposesof convenience in adjustment the control
grid connection to the coil L is made adjustable.
40 The reason `for connecting the grid .'I and the
anodel2, as shown, Vwill be hereinafter stated in
detail. The output circuit of the detector further
includes the screen grid electrode 8 which is con
_nected in series with the positive terminal of a
45
source of uni-directional current B through the
primary coil 9 of an audio frequency transformer
III. The negative terminal of the source B is con
nected by a lead I I to the low potential sides of
>the condenser 6 and the resistor 5. It is to be
clearly understood that the source B need not
be a direct current battery as shown on the draw
55
ing, but may be. any well known source of uni
directional current,.such as for example, the out
put terminals of a filter system employed for fil
tering rectified alternating current.
rThe secondary I2 of the transformer I0 may be
connected to any desired type of utilization means,
such as a loud speaker, since the output circuit
of the tube I is capable of _delivering a large audio
60
frequency output, in fact sufficiently large to
operate directly a loud speaker. However, there
maybe employed, between the screen `grid cir
cuit and the utilization means, a stage of audio
frequency amplification conventionally repre
sented as at D. In View of the fact that the de
tioning as a power detector, but simultaneously
adapted to operate as the control mechanism in
an automatic gain control system for the radio 10
frequency amplifier. This object is realized by ar
ranging the anode circuit of the detector tube I
tiñer to produce a direct current potential drop
across an impedance arranged between the anode
and the cathode, which drop may be utilized to
bias the preceding stages of the amplifier A.
More specifically, the said impedance comprises
a resistor R connected between the anode 2 and
a desiredV point on the grid bias resistor 5, the
connection to the latter preferably being made
adjustable. The potential drop across the re
sistor R is employed for biasing the radio fre
quency amplifier grid circuits by means of a lead 25
I3 having one end thereof connected to the low
potential side of the resistance R as at I 4, and
its opposite end connected to each of the grid
circuits of the radio frequency amplifier.
The latter connection to the grid circuits has 30
not been shown in detail for the reason that such
a connection is so well known to those skilled in
the art that the present description is believed
sufficient to indicate the manner in which the gain
control arrangement is to be constructed.
The '
lead I3 includes in series therewith a resistor I5,
a fixed capacity I6 being connected between the
negative side of the resistor I5 and the negative
side of the resistor 5. As is well known to those
skilled in the art the capacity I6 and resistor I5 40
function as a filter arrangement for the current
ñowing through the conductor I3.
=
The operation of the circuit is believed clear
from the aforegoing description, it being, addi
tionally, pointed out that the amplified received 45
energy is impressed across the electrodes ‘I and 3,
the detected energy being taken off the screen
grid circuit, anode rectification being employed,
and the detected energy being amplified and
utilized. With regard to the action of the anode 50
2 and cathode 3 as a diode rectifier, it will be
noted that the anode 2 does not have any steady
positive potential applied to it in the customary
manner, but is rather maintained at a negative
biasy with respect to the cathode 3 by means 55
of tap I‘I.
It will now be understood that during the pos
itive halves of the received carrier swings, elec
trons'from the cathode flow towards the anode
and through the resistor R, thereby rendering
the point I4 more negative than the opposite end
of the resistor R. By virtue of the connection
of the lead I3 to the negative end of the re
sistor R, it is possible to employ the variations
of potential drop across the resistor R to bias the
grid circuits of the preceding amplifier stages in
tector circuit is of the power type, a single stage such a manner as to maintain a substantially
of audio frequency amplification will be suñ‘icient ‘_ uniform radio frequency voltage applied to the
to operate a loud speaker for all general purposes detector for a wide range of signal levels at the
'in reproducing broadcast programs. It will, thus, amplifierinput. It has been found extremely 70
be seen that the cathode 3, control grid 1, and desirable tol make the direct current drop across
screen grid 8 cooperate to function as a triode the resistor R start at a carrier level well below
that required to overload the control grid l.
detector employing anode rectification and ad
ditionally that the screen grid electrode functions This result may be obtained by either or both of
two methods.' By adjusting the direct current 75
75". las the anode of a ‘detector tube. Of course the '
2504851738;
bias-'between anode 2- and cathode vâ'through the
position of tap l ‘l toa value lower than the direct:
current bias between Athe -control grid 7 and the.'y
cathode 3,' an increasing carrier voltage applied--V
to the systemy will cause useful biasing current .to>
flow in resistor R before the control .grid lcircuitV
3. ,
and to'the‘anode, means in the lcathode circuit ~for
biasing. the control grid- negative with respect to
the cathode, means for maintaining the screenl
gridpositive >with- yrespect to the cathode, means
overloads. It will also=beseen that bil-adjusting',
for, maintaining the anode at an average poten
tial less ;positive than the cathode, and means>
including an impedance connected between thev
the connection of the control grid T to alpoint on>
anode and cathodafor automatically controlling
the supply circuit L, C, of lower carrier-frequency
10 potential than that applied to anode 2, an in
the gain of said amplifier, and at least one stage
of audio frequency amplification coupled to the 10l
creasing carrier voltage applied to the system willv
screen grid circuit.
cause current to‘flow in resistor R before .the con-
5; In combination, a radio frequency amplifier,
a Adetector stage including an electron discharge
tube provided withV a cathode, control grid, screen
grid and anode, a tunable oscillatory circuit con
nected between the control grid and the cathode
and to the anode, means in the cathode circuit
for biasing the control grid negative with respect
tothe cathode, means for maintaining the screen
grid positive with respect to the cathode, means
for maintaining the anode at an average poten
tial less positive than the cathode, and means
including an impedance connected between the
trol grid circuit overloads, even -though tap I1
were brought to the lower end of cathode -biasi
While I have indicated and described one ar
rangement for Ycarrying .my invention into- effect,
it will be apparent to one skilled in the art that
my invention is by no means limited to the par
ticular organization shown and described but
that many modifications may be made without~
departing from the scope of my invention as set>
forth in the appended claims.
What I claim is:
1. In combination, a radio frequency amplifier,v
a detector stage including an electron discharge
tube provided with a cathode, control grid, screen:
grid and anode, a tunable oscillatory circuitcon-r
nected between the control grid and the cathode
and to said anode, means in the cathode circuit
for biasing the control grid negative with respect
to the cathode, means for maintaining thescreen
grid positive with respect to the cathode, means
for maintaining the anode at an average poten
tial less positive than the- cathode, and means in-cluding an impedance» connected between the
anode and cathode, for automatically controlling
the gain of said amplifier.
2. In combination, a radio frequency amplifier',
a detector stage including Aan electron discharge
tube provided with a cathode, control grid», screen
grid and anode, a tunable oscillatory-circuit con
anode and cathode, for automatically controlling
the` gain of said ampliñer, said impedance com 25
prising a resistor connected between the anode
and the control grid biasing means.
6. In combination, a radio frequency amplifier,
adetector stage including an electron discharge
tube provided with a cathode, control grid, screen 30
grid and anode, a tunable oscillatory circuit con
nected between the control grid ,and the cathode.,
means in the cathode circuit for biasing the con
trol grid negative with respect to the cathode,l
means for maintaining the screen grid positive
with respect to the cathode, means for maintain
ing the anode at an average potential less posi
tive than the cathode, and means including an
impedance connected between the anode and
cathode, for automatically controlling the gain
of said amplifier, said anode being connected to
the high potential side of said oscillatory circuit, _’
nected between the control grid and the cathode,
and said control grid being adjustably connected
means in the cathode circuit for biasing the con
to a point on said oscillatory circuit of a lesser
trol grid negative with respect to the cathode,
radio frequency potential than the point to which 45.
the anode is connected, said impedance compris
means for maintaining the screen grid positive
with respect to the cathode, means for main
taining the anode at an average potential less
positive than the cathode, and means including
an impedance connected between the-anode and`
cathode, for automatically controlling the gain
of said amplifier, said anode being connected 'to
a high potential point of said oscillatoryl circuit.A
3. In combination, a radio frequency amplifier,
a detector stage including an electron discharge
ingv a resistor connected between the anode and
said control grid biasing means.
7. A frequency changing circuit comprising a
space discharge device provided with a cathode,
control grid, screen grid and anode, an oscillatory
high frequency circuit connected between said
anode and cathode, high frequency current trans
mission means for connecting said control grid
to a point of said oscillatory circuit of lesser high
tube provided with a cathode, controlgrid, screen frequency potential than the point to which the
grid and anode, a tunable oscillatory circuit con-f said anode is connected, means for negatively
nected between the control grid and the cathode, biasing said control grid, means for positively
means in the cathode circuit for biasing the con
biasing said screen grid with respect to said an
60 trol grid negative with respect to the cathode,< ode and cathode, and a resistive path connected
60
means for maintaining the screen gridk positiveV between the anode and cathode whereby the an
with respect to the cathode, means for maintain
ode and cathode function as a diode rectifier.
ing the anode at an average potential less positive.
‘8; A frequency ychanging circuit comprising a
than the cathode, and means- including an im
space 'discharge device provided with a cathode,
pedance connected between the anode` and control grid, scr-een grid and anode, an oscilla 65
cathode, for automatically controlling the gain tory lcircuit connected between said anode and
of said ampliñer, said anode being connectedfto cathode, means for connecting said control grid
a point in said oscillatory circuit 4'of higher radio to a point of said oscillatory circuit, means for
frequency potential than the point to which the negatively biasing said control grid, means for
control grid is connected.
positively biasing said screen grid with respect to 70
4. In combination, a radio frequency amplifier,v said anode and cathode, and a resistive path con
a detector stage including an electron >discharge nected between the anode and cathode whereby
tube provided with a cathode, control grid, screen the anode and cathode function as a diode rec
grid and anode, a tunable oscillatory circuit con
tiñer,_a high frequency amplifier coupled to said
75 nected between the control gridand the cathode oscillatory'circuit, and means between the am
4
2,048,[email protected]
plifier and said> resistive'path for employing' the-
clúdi?g'îa tub`e provided with a cathode and at
potential drop across said path to control theV
gain of said amplifier.
9. A frequency changing circuit comprising a.
space discharge device provided with a cathode,
control grid, screen grid and anode, an oscilla
tory circuit connected between said anode andY
cathode, means for connecting said control grid
least three cold electrodes, an audio frequency
output circuit connected between one of the cold
electrodes and said cathode, a signal input net
work connected between a second one of the cold
electrodes and said cathode, the third of said
to a point of ' said oscillatory circuit, means for
10 negatively biasing said control grid, means for
positively biasing said screen grid with respect to
said anode and cathode, and a resistive path con
nected between the anode and cathode whereby
the anode and cathode function as a diode rec
tifier, a high gain radio frequency amplifier cou
pled to said oscillatory circuit, at least one stage
of audio frequency amplification coupled to the
screen grid circuit, and means connected between
cold electrodes being connected to said input net
work, both said second and third cold electrodes
being connected to 'the high alternating current
potential side of said network, a resistor in cir
cuit with at least said secondcold electrode and
said cathode for'developing a direct current gain
control bias for said amplifier tube, and a direct
current connection between a point of negative
potential on said resistor and the said gain con
trol electrode.
'
Y
Í
14. In a radio receiver utilizing a single heated
source of electron emission for a plurality of elec
ñer, a detector stage including an electron dis
tron paths, the method of reproducing radio fre
quency signals into perceptible condition at uni
form volume which comprises, amplifying said
signals atI a frequency above audibility, translat
ing said amplified signals into audio frequency
charge tube provided with a cathode, control grid,
signals with a substantial
said amplifier and said resistive path for employ
20 ing the potential drop across said path to control
the gain of said amplifier.
-10. In combination, a radio frequency ampli
translation
gain
25 screen grid, and anode, means for impressing
thròughone of said electron paths, rectifying a
radio frequency amplifier output voltage -between
component of said amplified >signals through an
otherfof said paths', utilizing said rectified signal
the control grid and cathode, »means for biasing
the control grid negative to the cathode, means
for maintaining the screen grid positive with re
30 spect to the cathode, means for impressing radio
frequency amplifier output voltage between anode
and cathode, means for maintaining the average
anode potential less positive than the cathode,
and means, including a resistance connected be
35 tween anocle and cathode, for furnishing a rec
tified potential for automatically controlling the
component in regulating the amplification of the
signals 'above audibility, and translating said
audio> frequency signals into perceptible condi 30
tion.
A
‘
Y
»
15. In a'radio receiver utilizing a single heated
source of electron> emission for a plurality of
electron paths,the method of reproducing radio
frequency signals into perceptible condition at 35
uniform volume which comprises, amplifying said
1l. In combination with a radio frequency am
signals -at a frequency above audibility, trans
lating said amplified signals into audio frequency
plifier of the type including at least one tube pro
signals with a substantial vtranslation gain through
gain of said amplifier.
_
404 vided with a gain control electrode, a stage fol
lowing the amplifier including a tube provided
with a cathode and at least three cold electrodes,
an audio frequency output circuit connected be
tween one of the cold electrodes and said cathode,
- a tuned radio frequency input circuit connected
between a second of said cold electrodes and said
cathode, the third cold electrode being connected
to a point on said input circuit of lesser'radio fre
quency potential than the point to which the
second cold electrode is connected, a path, includ
ing an impedance, connected between the second
cold electrode and the cathode to provide a gain
control bias for the said ampliler tube, and a
direct current connection between the path and
Ul Dlf a the gain control electrode of the amplifier tube.
12. In combination with a high frequency am
plifier tube provided with a gain control electrode,
a detector tube including a cathode, a grid, aA
cold positive electrode, and an auxiliary cold elec
60 trode, a tunable oscillation circuit connected be-A
tween the auxiliary electrode and the cathode,
an audio frequency output circuit connected be-tween the cathode and the positive electrode, the
grid being Vconnected to the tunable circuit,
'l means for biasing the grid to render the cathode,
grid and positive electrode operative as an anode
detection circuit, means for connecting the auxil
iary electrode and cathode to provide a diode rec
tifier, and a direct current connection between
70 " the auxiliary electrode and said gain control elec
trode of the amplifier tube.
13. In combination with a radio frequency sig
nal ampliñer of the type including at least one
tube provided with a gain control electrode, a
75-4 detector stage following the amplifier and in
25
one of said electron paths, rectifying a component
of said amplified signals through another of said
paths, filtering said' rectified component to elimi
nate a substantial pulsating component there
from, developing from said rectified and filtered
component a regulating potential, utilizing said
potential to regulate the amplification of signals`
above audibility, andl translating said audio fre
quency signals into audible signals.
16. In a radio receiver including an amplifier
having means to regulate the degree of amplifica 50
tion to be effected thereindetermined by a biasing
potential, and a detector of the electron discharge
type utilizing'a single heated source of electron
emission for a plurality of electron paths, the
method Aof reproducing radio frequency signals
into -perceptible condition at uniform volume
which comprises, amplifying signals at a fre
quency above audibility, utilizing one electron
pathto translate said amplified signals into audio
frequency signals and to amplify the same, also 60
utilizing another electron path to rectify the car
rier wave component of the first-mentioned am
plified signals, employing said rectified carrier
wave component to develop a biasing potential,
applying said biasing potential to regulate the
signal amplification effected above audible fre
quencies, and translating said audio frequency
signals into perceptible condition.
L 17.' In a radio receiver including an amplifier
provided with means to regulate the degree of
amplification to be effected therein as determined
by a biasing potential, and a detector o-f the elec
tron discharge type utilizing a single heated source
of` electron emission for a plurality of electron
paths', the methodiof reproducing radio frequency 75
2,048,738
' signals into perceptible condition at uniform
volume which comprises, amplifying signals at a
frequency above audibility, utilizing one electron
path to translate said amplified signals into audio
frequency signals With an appreciable translation
gain and utilizing another electron path to rec
tify the carrier Wave component of the amplified
signal, employing said rectified carrier wave com
ponent to develop a biasing potential, and apply
10 ing said biasing potential to said amplifier to
regulate the amplification effected therein, and
translating said audio frequency signals into
perceptible condition.
18. In a radio receiver including an amplifier
15 for amplifying radio- frequency signals, said am
plifier having means to regulate the degree of
amplification effected therein as determined by
a biasing potential, and a detector of the ther
mionic type utilizing a single heated source of
20 electron emission for a plurality of electron paths,
the method of reproducing radio frequency sig
nals into perceptible condition at uniform volume
which comprises, amplifying said signals at a
frequency above audibility, developing electron
25 emission from said source, utilizing a portion of
said electron emission in one path to translate
said amplified signal into audio frequency signals
and to amplify the same, utilizing another por
tion of said electron emission in another path to
30 develop a rectified current corresponding to the
carrier wave component of said first-mentioned
ampliñed signals, employing said rectified current
to generate a biasing potential, utilizing said bias
ing potential to regulate the amplification of said
35 first-mentioned signals, and translating said
audio frequency signals into perceptible condition.
19. In a radio receiver, an amplifying stage in
cluding a vacuum tube operating to amplify sig
nals at frequencies above audibility, a detector
40 having a vacuum tube provided with a first elec
trode, a second electrode, a third electrode, and a
cathode, anv input circuit for said detector linked
to said amplifier, said input circuit including said
cathode and one of said electrodes, an output
45 circuit including said cathode and another of said
electrodes, a rectifier circuit including a portion
of said input circuit, an additional one of said
electrodes and said cathode, said rectifier circuit
È
serving to rectify the carrier component of said
amplified signal, means for developing a potential
according to said rectified carrier component, and
means for utilizing said potential to control the
amplification effected in said amplifying stage.
5
20. In a radio frequency signaling system, means
for amplifying signals at frequencies above audi
bility, means including one heated electron source
for translating said amplified signals into audio
frequency signals with a substantial translation 10
gain, means including said heated electron source
for rectifying a component of said amplified sig
nals, means controlled by said rectified signal
component and including a portion of said am
plifying means for regulating the amplification 15
effected by said amplifying means, and means for
reproducing said audio frequency signals into
perceptible form.
'
21. In a radio frequency signaling system,
means for amplifying signals at frequencies above
audibility, means including one heated electron
source for translating said amplified signals into
audio frequency signals with a substantial trans
lation gain, means including said heated electron
source for rectifying a component of said ampli 25
fied signals, means for filtering said rectified sig
nal component, means controlled by said filtered
signal component and including a portion of said
amplifying means for regulating the amplifica
tion effected by said amplifying means, and means 30
for reproducing said audio frequency signals into
perceptible form.
22. In a radio frequency signaling system,
means for amplifying signals at frequencies above
audibility under the control of a biasing potential, 35
means including one heated electron source for
translating said amplified signals into audio fre
quency signals with a substantial translation
gain, means including said heated electron source
for rectifying a component of said amplified sig 40
nals, means controlled by said rectified signal
component for controlling the biasing of said
amplifying means whereby the amplification
effected by Said amplifying means is regulated,
and means for reproducing said audio frequency
signals into perceptible form.
PAUL O. FARNHAM.
45
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