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Патент USA US2410982

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Nov. 12, 1946.
234N382
W. R. KOCH
RECORD REPRODUCTION CIRCUIT
Original Filed 0c_t. 6, 1942
2 Sheets-Sheet 1
FM
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AMPLIFIER '
DETECTOR
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INVENTORQ
W/A/F/ELD R. KOCH
IIBY
ATTORNEY
' Nov. 12, E946.
2,410,982
‘ w. R. KOCH_ ‘
RECORD REPRODUCTION CIRCUIT
Original Filed Oct. 6, 1942
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.INVENTOR.
WM/F/ELD R. KOCH
BY )
ATTORNEY
-
Patented Nov. 12, 1946 7
2,410,982
UNITED STATES PATENT OFFICE? i
'Win?eld R.,Kojch, Iiiaddon?eld, N. 11., assignor to ,
Radio Corporation of America, a corporation of‘
Delaware
‘Original application October 6, 1942, Serial No.
460,940, now Patent No. 2,361,634, dated'OctOber
31,1944. Divided and this application Sep
tember 16, 1943, Serial No. 502,589
12 Claims (Cl. 179-4004)
1
2
My present invention relates generally .to pho
o
to be associated with the stylus of capacity pick
up I is not shown, and the latter is schematically
nograph record reproduction circuits, andv more
especially to circuits of thegeneral type utilizing
represented as consisting of a pair of spaced met
a frequency modulation oscillator having a ca
al plates. However, it should be "clearly under
pacity pickup. This application is a division of
stood that thepickup device I may be replaced
by any variable reactance device, such as a micro
my application Serial No. 460,940, ?led October
6, 1942, now Patent No. 2,361,634, granted October
phone or pressure-responsive element. The
stylus plate (usually a ribbon) is connected-to
the grounded sheath of the high impedance .co
C. M. Sinnett has disclosed in his application
Serial No. 459,375, ?led September 23, 1942, a 10 axial cable 2. The immobile plate is connected
31, 1944.
,
system for reproducing phonograph records with
to the inner conductor; the latter is connected
high ?delity and high gain, but with minimum
to the high alternatingpoténtial side of Ithe'os'cil
production cost. In general, the system com
lator tank circuit.
.
prises a capacity pickup device capable of con
The oscillator tube 3 may be a GSA’? 'type‘tube
verting recorded sound waves into frequency 15 whose cathode is returned to an intermediate
point on the adjustable inductance coil 4. The
modulated high frequency waves, a discrimina
latter is schematically represented as being of the
tor-recti?er network being used to derive from
the modulated waves the original audio signals
powdered-iron core type; condenser 5 shuntsv the
which had been recorded. The system has other
coil to resonate the same to the mean, or center,
uses. Microphones and pressure-responsive pick
frequency of the oscillator. In general, the pick-,
. up I and capacity of cable 2 and condenser 5.
ups can be employed as the input devices. 7
One of the main objects of my invention is to
provide the normal resonating capacity for the
provide various improved circuits of the same
coil 4. The first grid 6 is connected backito‘the
, high alternating potential side of .coil d‘by'the
general type, but wherein sensitivity, ?delity and
economy are extended to a further "degree.
25
The novel features which I believe ‘ to be
characteristic of my invention are set forth with‘ ‘
particularity in the appended claims; the inven
tion itself, however, as to both its organization
usual blocking condenser v‘I, and grid return ‘re
sistor 8 connects the grid 6 to ground. The sec
ond, third and fourth grids are tied together to
function as an effective ‘single electrode, and are
supplied with approximately +100 volts thereby
and method of operation will best be understood 30 providing a positive oscillator anode which is des
ignated by numeral 9.
a
by reference to the following description taken
Circuit 5-44 has a normal or mean frequency
in connection with the drawings, in which I have
which is varied by changes in capacitance of the
indicated diagrammatically several circuit or
pickup. The capacitance changes occur by vir
ganizations whereby my invention may be carried
into effect.
35 tue of motion of the stylus produced. by the riding
In the drawings:
,
‘ of the latter through the record grooves.
_
Fig. 1 shows an embodiment of the invention,
As a
result-of the capacitance variations of pickup I,
the frequency of the oscillator tank circuit will
be varied. The frequency deviation relative to
Fig. 2 shows a modi?cation wherein an and 40 the mean frequency may extend to any desired
pli?er of the modulated waves is concurrently
frequency value. For example, an overall fre
quency deviation of 30 kilocy'cles (kc) may-be
used as a detector,
‘
, j
employed. The mean frequency can be of the
Fig. 3 is a modi?cation of the circuit-of Fig. 2,
the oscillator functioning simultaneously as a
order of 30 megacycles (mc.). These are purely
wherein the modulated wave energy across the
discriminator is greatly increased,
recti?er,
45 illustrative values.
Fig. 4 is an embodiment wherein the detector
is of the multi-grid type,
.
Fig. 5 is a variation of the-circuit of Fig. 4, ‘the
a
The frequency modulated (FM hereinafter ‘for
brevity) high frequency oscillations appear-in the
circuit connected'to plate i9 by virtue 'of elec
Referring now to the accompanying drawings,
‘wherein like reference .charactersin the different
?gures designate similar circuit elements, it will
tron coupling between the oscillator section of
tube 3 and plate It. :The' electron coupling phe
nomenonis well known, and it is sufficient for
the purposes of this application to point out that
be understood that the systems disclosedherein
the FM signal energy appearing in the plate cir
oscillator acting as a, detector.
aregenerally of the type describedand claimed
cuit of tube-3 is ampli?ed. Asecond-tube is pro
in the aforesaid Sinnett application. The record 55 vided, and this tube is designated by numeral
2,410,982
3
||. The tube may be one of the pentode-diode
type wherein there is an electrode | 2 functioning
as a diode anode.
The anode I2 is adjacentv
cathode l3 which is grounded. The pentode sec
tion of the tube comprises the cathode l3, plate
l4 and three intermediate grids designated l5,
l6 and IT.
The intermediate, or screen, grid I6 is con
nected to the source of potential of oscillator
anode 9, the connection between these electrodes
being bypassed to ground by condenser l8 for
high frequency currents. The control grid I5
is coupled to the high potential side of the oscil
lator tank circuit by coupling condenser l9, re
sistor 20 returning grid l5 to ground. Plates l0
and M are connected in common to a point of
approximately +200 volts through the coil 2| of
the discriminator circuit. This coil 2| is sche
matically represented as having a powdered iron
4
oscillator tube 3 is connected to the positive volt
age source Which feeds the oscillator anode 9 and
the screen grids of the following ampli?er tube.
Otherwise, the oscillator circuit of Fig. 2 is sim
ilar to that shown in Fig. 1. The ampli?er tube
is a pentagrid tube, andinay be of the GSA’? type.
The tube is designated by numeral 30, and its
cathode 3| is connected to an intermediate point
on the coil 2| of discriminator circuit 2|—-22.
In this modi?cation the high potential side of
the discriminator circuit is connected to the plate
32 of tube 30 by the coupling condenser 33, while
the low potential side of the discriminator circuit
is grounded. The choke coil 25 and series load
resistor 24 are arranged between plate 32 and
ground.
The control grid 34 of tube 30 is coupled, as
in Fig. 1, to the high alternating potential side
core.
of oscillator circuit 4—5. It will be noted that
the second, third and fourth grids of tube 30
record, and the corresponding amplitude modu
the pickup device.
The condenser 22 shunts coil 2|, and pro- _
vides a resonant circuit.
are tied together, and effectively function as a
common screen electrode. The cathode 3| and
The core of coil 2| is adjusted so that the
plate 32 of tube 30 cooperate to provide diode
discriminator circuit 2|-22 has a single peak
recti?cation. It will be noted that the discrimi
resonance curve. The peak frequency is either
nator circuit 2|—22 is arranged in the cathode
above or below the mean, or center, frequency of
circuit of tube 30. This is very similar to the
the FM signals. By way of illustration, the cen
oscillator circuit used, except that in the oscil~
ter frequency may be located at an intermediate
lator the control grid is affected from its own
point of either slope of the resonance curve of
cathode circuit instead of from an external source
circuit 2|-22. It is desirable to have these
slopes as linear as possible. Hence, it is seen that 30 of voltage as in the case of ampli?er operation.
The voltage gain is all supplied by the step-up
discrimination occurs, and that the FM signal
secured from the tuned circuit 2 |-22. The dis
energy developed across the plate circuit of the
criminator circuit is, of course, slightly mistuned
oscillator is transformed at circuit 2|-;22 into
as in the case of Fig. 1, so as to secure an am
corresponding amplitude modulated wave energy.
The frequency deviations of the FM signals cor 35 plitude variation corresponding to the frequency
deviation introduced by the capacity change in
respond to the sound waves of the phonograph
In Fig. 2, the plate current of tube 3 does not
feed directly into the discriminator circuit 2 |—22.
40 The oscillator voltage is applied to the control
grid 34 of tube 30 from the high potential side
ti?ed by‘the diode |2--|3. Anode I2 is coupled
lated wave energy similarly corresponds to the
recorded sound waves.
The amplitude modulated wave energy is rec
by condenser 23 to the high potential side of coil '
of circuit 4-5.
The tube 30 acts as a cathode
follower ampli?er. The output voltage of tube
2|. The modulation voltage is developed across
30 is stepped up‘ and shifted in phase because of
a load resistor 24 arranged in series with the
radio frequency choke coil 25 between anode l2 45 the tapping point of cathode 3| on coil 2|. The
said output voltage is applied to the plate 32 of
and ground. The high frequency bypass con
tube 30. The plate 32 cooperates with cathode
denser 26 shunts resistor 24. The modulation
3| to provide a recti?er, and in this respect is
signals derived from resistor 24 may be trans
similar to diode |3—|2 of Fig. 1. However, the
mitted to any form of audio utilizing circuit.
By using the pentode-diode tube II it is possi 50 recti?er of Fig. 2 is grid-controlled. The recti
?er path between cathode 3| and plate 32 is con
ble to have the pentode section in parallel with
trolled in phase with the voltage of grid 34.
the ampli?er part of the oscillator tube 3. The
The detector of Fig. 2, therefore, is a grid-con
radio frequency voltage is thereby increased
trolled recti?er. Whenv grid 34 is positive relative
across discriminator circuit 2|—22 to a value of
over double the magnitude that would be secured 55 to cathode 3| space current flows through the
tube, and diode recti?cation can take place.
by feeding the diode directly from the plate of
When grid 34 is negative no space current flows.
the oscillator. In this way sufficient audio fre
Recti?cation by 3|-32 cannot take place. Be
quency voltage is derived from a simple diode
cause of the phase shift between the voltage ap
recti?er to operate the audio frequency ampli?er.
The circuit is free from possible noises which 60 plied to grid 34 and that applied to plate 32
(which changes in accordance with the change
would ordinarily be introduced in a voltage-dou
in oscillator frequency) the output voltage across
bler diode circuit through leakage. Because of
resistor 24 contains audio frequency currents,
the high frequencies employed, short leads are
Each of Figs. 2, 3, 4 and 5 employs the passive
desirable. By giving grid resistor 20 a value of
about 40,000 ohms the grid is driven further 65 discriminator circuit 2|-—22 in the cathode lead
of the ampli?er tube. The difference in these
positive, and considerably more radio frequency
four circuits is in the manner of securing detec
output voltage is obtained across the discrimina
tion of the resulting amplitude-modulated wave
tor circuit. The choke coil 25 affects the “Q” of
energy. Because of the slight mistuning there is
the discriminator very little. In general, then,
it will be seen that in the circuit of Fig. 1 the 70 also present a difference in phase of the oscil
lator and discriminator circuit voltages, which
FM signal energy is fed into the discriminator
varies when the frequency is varied. This is uti
circuit by electron coupling in tube 3, and is con
lized in the detector circuits to give a greater
currently transmitted from tube II by the am
output than would be secured by depending on
pli?er action of the pentode section of tube | I .
In the arrangement of Fig. 2, the plate III ,of 75 amplitude variations alone. ‘This action is ex
‘i 291110982
.6
F'plained asfollows: Whenthe grid of eitherthe
334 and 143 yields aiplate current containing-the
oscillator or ampli?er tubes is driven extremely
lfarfthe plate current will ?ow in the tube only
v‘for short intervals during the extreme positive
operation of the radio frequency voltage. When
‘audiolfrequency components.
there exists a phase difference between these im
'
I ‘Thearrangement of Fig. 5 differs ‘from'that
shown in ‘Fig. 4 in that the oscillator tube 3 is
givenithe additional function of acting as the
multi-grid detector‘ which was described in con
pulses of current arriving at the anode and the
nection with Fig. 4. This is accomplished‘ by hav
“voltage'applied to the‘anode by the discriminator
ing the second and fourth grids of tube 3 acting
rcircuit, only during a short period can this plate
.as’the oscillator anode 9, while the intermediate
current ?ow. If the phase of the voltage di?ers 10 grid!) is connected by lead 60 to the junction of
su?iciently then no plate current can flow. If
condenser 45 and resistor 44. The plate of tube
it is in phase with the current, the maximum
‘to ‘is tied to the second, third and fourth grids
‘plate current can ?ow. Variation of the oscillator
lof-‘the tube, and have in common a positive'po
(frequency will cause plate current to vary be-V ltential applied thereto. The plate‘ ll] of the os
"tween-these extremes. By using the voltage drop 15 cillator'tube 3 isconnected to the load resistor
across the series resistor the audio frequency out
50 across which latter resistor is "developed ‘the
put voltage canv be secured.
>
1 audio frequency‘ voltage. In Fig. 5, the ampli?er
‘Referring now to Fig. 3, it is-pointed out that
tube 40 acts as a cathode follower ampli?er.
in this modi?cation the'plate l 0 acts as the anode
The stepped-up and phase-shifted voltage 'de
of a diode recti?er consisting of anode H] and
velopedacross 2!-—22 is applied to grid 9' of the
cathode3l of tube 39. The action is similar to
‘tube v3. The variable phase between the voltages
that described in connection with Fig. 2. In this
applied to the ?rst and third‘grids of tube '3 causes
arrangement the plate 32 isrtied to the positive
the plate current of tube 3 .to vary accordingly.
screen assembly of tube 13!}. The discriminator
In this way there is secured across the load re
circuit .2I—-22 is in the cathode circuit of tube 25 sistor 50 plate current having audio frequency
30. ‘In other words, in Fig. 3 besides functioning
as the output electrode of the ampli?er section
The circuits shown in Figs. 2, 3, ‘4 and‘5 have
components.
'
‘
'
.of oscillator tube 3, the plate is additionally
the advantage of employing standard commercial
types of tubes, and only 100 volts of +B ‘supply
ti?er of the amplitude modulated wave energy 30 is required. It should, also, be noted that the
developed by the discriminator circuit 2 i—22. It
pair of tubes required in these circuits can be of
is, again,emphasized that by virtue of the phase
the same type, thereby simplifying manufacture
shift noted above, sharper discrimination is se
and servicing. The tubes used (6SA'7) have
cured. The variation in voltage applied to plate
helical heaters thereby reducing any hum modu
In, because of the selectivity of the discriminator
lation. If desired, in Figs. 4 and 5 the plate re
circuit, is accompanied by a change in phase
sistor ‘50 may be returned to ground, instead of
thereby enhancing the recti?er output variation
to-the positive potential point.
responsive to frequency change.
While I have indicated and described several
In Figs. 4 and 5, recti?cationis‘secured by a
systems for carrying my invention into effect, '
multi-grid detector.‘ In the modi?cation of Fig.‘
it will be apparent to» one skilled in the art that
4, the plate H] of oscillator tube .3 ‘is connected
my invention is by no means limited to the par
to the tied grids 9. The detector tube is desig
ticular organizations shown and described, but
nated by numeral 40, and may be a pentagrid
‘that many modi?cations may be made without
'functions'as the anode of a grid-controlled rec
tube of the GSA’? type. The control grid 34 is
departing from the scope of my invention, as set
connected to the oscillator grid of tube 3. The'
forth in the appended claims.
second and fourth grids of tube 40, designated
What I claim is:
by numerals lil and 42 respectively, are connected
1. In combination, a tube provided with an
to the plate is and grids 9. The control grid 43,
‘oscillator section and a postive output electrode,
located between, grids ill and 42, is connected to
means connected to said oscillator section to
ground by a resistor M, and condenser 45 couples 50 provide angular velocity-modulated oscillations
the grid to the high potential side of the dis
which have a predetermined mean frequency,
criminator circuit. The plate 32 of tube 40 pro
electron coupling between said oscillator section
vides the audio voltage across 'the output load re
‘and said output electrode developing said angular
sistor 50, and the lower end of resistor 50 is con
velocity-modulated oscillations in the output
nected to a source of positive potential. The load 55 electrode circuit, a resonant circuit connected
resistor 50 is shunted to ground by the high fre
‘to said output electrode, ‘said resonant circuit
quency bypass condenser 5|. In Fig. 4, as the
‘being tuned to a frequency suiiiciently different
frequency of the oscillations changes, the phase
from ‘said mean frequency to permit the resonant
‘of the voltage applied to grid 43 will vary from
circuit to function as a discriminator circuit, an
that applied to grid 34. If the oscillator fre
electron ‘discharge device having an input elec
quency changes enough to produce resonance of
trode coupled to said oscillator section, said de
the discriminator circuit, the two grid voltages
vice having an output electrode coupled to said
will be in phase and maximum plate current will
discriminator circuit.
?ow. By limiting the swing to one side of the
2. In combination, a tube provided with an
oscillator section and a positive output electrode,
discriminator, the plate current will vary from
means connected to said oscillator section to
this maximum to a lowvalue. Both grids are,
‘provide angular velocity-modulated oscillations
of course, supplied with sufficient voltage so that
which have a predetermined mean frequency,
the tube is operated on a non-linear portion of
electron coupling between said oscillator section
its characteristic. Tube ‘it, in this modi?cation,
acts as a cathode follower ampli?er. A voltage 70 and said output electrode developing said angular
velocity-modulated oscillations in the output elec
from the oscillator tank circuit 5-4 is applied to
trode circuit, a resonant circuit connected to
grid 34. The stepped-up and phase-shifted volt
age is applied togrid 43. The Variable phase be
tween the alternating voltages impressed ‘on grids
‘said output electrode, said resonant circuit being
tuned to a frequency sui?ciently different from
‘said mean frequency to permit the resonant cir
‘2,410,982
r- 7
cult to .function as a discriminator circuit, an
electron discharge device having an input elec
trode coupled to said oscillator section, said de
vice having an output electrode coupled to said
discriminator circuit, and a recti?er coupled to
said discriminator circuit for developing modula
tion voltage,
,
3. In combination, a tube provided with an
oscillator section and a positive output electrode,
ing an input electrode coupled to said oscillator
section, said device having an output electrode
coupled to said resonant circuit, and a recti?er
coupled to said resonant circuit for developing
modulation voltage.
7. In combination, a tube provided with an
oscillator section and a positive output electrode,
means coupled to said oscillator section to pro
vide
angular
velocity-modulated
oscillations
means connected to said oscillator section to pro 10 which have a predetermined mean frequency,
electron coupling between said oscillator section
vide angular velocity-modulated oscillations
and said output electrode developing said angular
which have a predetermined mean frequency,
velocity-modulated oscillations in the output
electrode circuit, a resonant circuit connected to
' velocity-modulated oscillations in the output 15 said output electrode, said resonant circuit acting
electron coupling between saidoscillator section
v and said output electrode developing said angular
electrode circuit, a resonant circuit connected to
said output electrode, said resonant circuit being
tuned to a frequency sufficiently different from
said mean frequency to permit the resonant cir
as a discriminator circuit, an electron discharge
device having an input electrode coupled to said
oscillator section, said device having an output
electrode coupled to said discriminator circuit,
cuit to function as a discriminator circuit, an 20 said last named electron discharge device in
cluding at least a cathode having said discrimina
electron discharge device having an input elec
tor circuit in the space current path thereof.
trode coupled to said oscillator section, said de
8. In combination, a tube provided with an
vice having an output electrode coupled to said
oscillator section and a positive output electrode,
discriminator circuit, said last named electron
discharge device including at least a cathode 25 means connected to said oscillator section to pro
vide angular velocity-modulated oscillations
having said discriminator circuit in the space
which have a predetermined mean frequency,
current path thereof.
electron coupling between said oscillator section
4. In combination, a tube provided with an
and said output electrode developing said angular
oscillator section and a positive output electrode,
means connected to said oscillator section to 30 velocity-modulated oscillations in the output elec
trode circuit, a resonant circuit connected to said
provide angular velocity-modulated oscillations
output electrode, said resonant circuit being
which have a predetermined mean frequency,
tuned to a frequency su?iciently diiferent from
electron coupling between said oscillator section
said mean frequency to permit the resonant cir
and said output electrode developing said angular
velocity-modulated oscillations in the output elec 35 cuit to function as a discriminator circuit, an
electron discharge device having an input elec
trode circuit, a resonant circuit connected to
trode coupled to said oscillator section, said device
said output electrode, said resonant circuit being
having an output electrode coupled to said dis
tuned to a frequency sufficiently different from
criminator circuit, the output electrode of said
said mean frequency to permit the resonant cir
cuit to function as a discriminator circuit, an 40 ?rst mentioned tube and the cathode of said elec
tron discharge device functioning as a rectifier to
electron discharge device having an input elec
rectify amplitude modulated Wave energy appear
trode coupled to said oscillator section, said de
ing across said discriminator circuit, and the dis
vice having an output electrode coupled to said
criminator circuit being in the space current path
discriminator circuit, the output electrode of said
of said device.
?rst mentioned tube and the cathode of said
electron discharge device functioning as a recti
9. In combination with an oscillator of variable
frequency, an electron discharge tube having at
?er to rectify amplitude modulated wave energy
appearing across said discriminator circuit.
.least a cathode, control grid and anode, means
for coupling said grid to said oscillator thereby
5. In combination, a tube provided with an
oscillator section and a positive output electrode, 50 to vary the grid voltage at the variable frequency,
a frequency discriminator circuit having one side
means coupled to said oscillator section to pro
vide angular velocity-modulated oscillations
thereof at an invariable potential, means con
necting the anode to a point of higher alternating
which have a predetermined mean frequency,
potential on the discriminator circuit than the
electron coupling between said oscillator section
and said output electrode developing said angular
cathode, a load impedance in circuit with said
velocity-modulated oscillations in the output elec
cathode and anode to provide a recti?er circuit,
and said grid controlling the space current be
trode circuit, a resonant circuit connected to said
output electrode, said resonant circuit being tuned
tween the cathode and anode.
to a frequency su?iciently different from said
10. In combination with a tuned circuit having
mean frequency to permit the resonant circuit 60. a frequency-varying element connected thereto,
to function as a discriminator circuit, an ampli
an electron discharge tube having at least a cath
?er tube separate from the ?rst tube having an
ode, grid and anode electrode operatively asso
input electrode coupled to said oscillator section,
ciated with the tuned circuit to provide an oscil
said tube having an output electrode coupled to
latory circuit of variable frequency, a second
said discriminator circuit.
65 electron discharge device having at least a cath
6. In combination, a tube provided with an
oscillator section and a positive output electrode,
means coupled to said oscillator section to provide
ode, control grid and positive cold electrode,
means supplying oscillatory voltage from the
tuned circuit to said second device control grid, a
angular velocity-modulated oscillations which
frequency discriminator circuit connected in the
have a predetermined mean frequency, electron 70 space current path of the second device and
adapted to be traversed by the space current of
coupling between said oscillator section and said
the second device, means connecting the cathode
output electrode developing said angular velocity
of said second device to an intermediate potential
modulated oscillations in the output electrode
point on the discriminator circuit, and a resistive
circuit, a resonant circuit connected to said out
load in circuit with the discriminator circuit
put electrode, an electron discharge device hav
2,410,982
9
10
across which is developed detected voltages from
currents ?owing through the discriminator cir
cuit.
11. In a record reproducer system, a tube pro
vided with oscillator electrodes, means connected
to the oscillator electrodes to provide angular ve
locity-modulated oscillations which have a de
sired mean frequency, a frequency discriminator
sponsive to said oscillations for controlling the
space current path.
12. In a record reproducer system, a tube pro
vided with oscillator electrodes, means connected
to the oscillator electrodes to provide angular ve
locity-modulated oscillations which have a desired
mean frequency, a frequency discriminator cir
cuit, a second tube having said discriminator cir
circuit, an electron discharge tube having said
cuit in its space current path, means responsive
discriminator circuit directly connected in its 10 to said oscillations for controlling the space cur-.
space current path whereby the space current of
rent path of the second tube and recti?er means
the last mentioned tube ?ows through said dis
including the anode and cathode of the second
tube to derive modulation signal voltages from
. criminator circuit, a resistive load in circuit with
said discriminator circuit across which is de
said space current path.
veloped detected voltages from currents ?owing 1 15
WINFIELD R. KOCH.
through the discriminator circuit, and means re
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