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` pms, 1946.
A
HJ. wou.A _
2,412,023
TRANSDUCER SYSTEM
Filed Dec. 1, 1944
INVENTOR
ATTORNEY
2,412,023
Patented Dec. 3, 1946
UNITED STATES PATENT vOFFICE
2,412,023
TRANSDUCER SYSTEM
Harry J. Woll, Indianapolis, Ind., assigner to
Radio Corporation of America, a corporation of
Delaware
Application December 1, 1944, Serial No. 566,143
2
1
'provide a nigh fidelity,
My present invention relates generally to an
~ Still other features ef my invention will best
be understood by reference to the-following de
scription, taken in connection with the drawing,
spondingly relatively large variations of direct
in which I have indicated diagrammatically a
circuit organization whereby my invention may
current or potential.
In his application Serial No. 490,614, filed June
l2, 1943, U. S. Patent No. 2,371,373, issued March
13, 1945, A. Badmaieff has disclosed and claimed
be carried into effect.
‘
.
Fig. 1 shows an embodiment of my invention;
transducer for concurrently varying the fre
' and
Fig. 2 shows an idealresonance curve of the
quency of a source of oscillations and a discrim
inator reso-nant frequency in opposite senses
thereby to provide cancellation of even harmon
resonant plate circuit.
.
~
'
v
Reference is made to the aforesaid Badmaieff
patent for a detailed explanation of the advari-~
tages of utilizing the balanced form of transducer
for concurrent variation of oscillator tuning and
discriminat-or tuningv in opposite phase relation.
While the system disclosed herein is described in
ics, greatly to reduce distortion and to double
the discriminator output voltage. More speci
fically, Badmaieff disclosed an embodiment
wherein a push-pull form oi condenser pickup
concurrently, but in opposite senses, varied the
Y connection with record reproduction, it is to beA
frequency of the oscillator tank circuit of a multi
grid tube and the frequency of a discriminator
circuit located in the plate circuit of the multi
grid tube. He utilized a rectifier to derive from
clearly understood that it may be used for record
cutting, measurement devices,> Where linearity
and Ismall pickup area are desired, such ‘asfor
pressure measurement, liquid height measure
the plate circuit a voltage representative of the
25 ment,` elongation measurement, vibration meas
urement.
t is one of the important objects of my pres
ent invention to provide a more compact system
Where the pickup device is a micro
phone, the system could be used for hearing-aid
apparatus, public address systems, binaural sys
having operational advantages similar to those
of the Badmaieff system, but eliminating the need
for a special rectifier.
l
In the drawing: »
a method of, and means for, using a balanced
pick-up capacity variations.
low cost and low distor« ì
tion record reproducer system.
improved balanced transducer system, and more
particularly to a novel system for deriving from
small variations of electrical capacity into corre
tems and the like.
30
ì
v
The pickup device may be constructed in the
manner shown by Badmaieif in his aforesaid pat
Another important object of my invention is
to assign a double function to the oscillator grid
circuit of the aforesaid multi-grid tube; the os
cillator grid circuit in my invention acting to
ent, or it may be constructed in any other suit
'able manner to provide push-pull reactance
taining an audio frequency component.
Another, and more specific, object of this pres
ent invention is to provide a multi-grid tube hav~
ing a cathode and two cold electrodes adaptedA to-
ed with a record-scanning stylus. The circuit
operatively associated with the pickup device willY
changes. The pickup is, therefore, schematically
provide grid-leak detection whereby the plate 35 represented as comprising a pair of spaced fixedv
electrodes í and 2. Midway between the stators
circuit has current flowing therethrough con
function as a generator of high frequency os
cillations, whereas a cold output electrode is pro
I _and 2 is located a mobile electrode 3 provid- ‘
40
now be described.
.
The tube 4 in Fig. l is shown as of the pentode
type, although any other type tube may be used.
Itsrcathode 5 is connected to a low alternating
oscillator circuit by a predetermined amount, 45 potential tap 5 on the oscillator coil Ll. The coil
Ll is preferably. of the Variable inductance type,
vided With a resonant circuit mistuned from the
and a balanced reactive transducer being em
and has an adjustable core of comminuted iron.
ployed to vary the frequencies of the oscillator
The core is schematically shown. The control
circuit and resonant output circuit whereby the
grid
l, which functions asthe oscillator section
latter develops a voltage whose magnitude and
grid, is connected `through the direct `current
phase are dependent upon the oscillator fre 50 blockingcondenser 8 to the high alternating po
quency and the resonant output circuit frequency.
tential side of coil L! and to ñxed plate I of the>
Still other objects of my invention are to im
balanced . capacity pickup device.
The mobile
prove the simplicity, eiiiciency and reliability of
element 3 of the pickup device is Aconnected by
record reproduction systems of the frequency
lead 9 to the negative terminal -B, which may
modulation (FM) type, and more especially to 55 be ground,V of the direct current energizing source,
2,412,023
3
4
The positive terminal +B of the source may be '
either be in frequency or phase. Preferably. it
at +300 volts. The positive terminal +B is con
nected through resistor S’ to the cold electrode
I0 of multi-grid tube 4.
is desirable to adjust the iron core of coil L2 so
Electrode I0 functions as the oscillator anode
of the tube. The output electrode or plate Il
that the peak frequency of the discriminator
circuit is of a value such that the mean oscilla
tor frequency Fc falls at approximately '10% of
the response on one side of the resonance curve
characteristic of the discriminator circuit. Spe
has one connection through the directcurrent
cifically, and merely by way of illustration, Fc
blocking condenser I2 to the fixed plate or stator
could be 26 mc., while the plate coil L2 could be
2 of the balanced capacity pickup device. A
second conductor connects plate II to the high 10 normally tuned to 26.1 mc.
The oscillator grid condenser 8 is shunted by
alternating potential end o! the discriminator
grid leak resistor I6 thereby providing the means
coil L2 in accordance with my invention. The
for grid-leak detection at the oscillator grid.
coil L2 is, also, a variable inductance having
The numeral I1 indicates a coupling path from
a core of comminuted iron, and the low poten
tial end of coil L2 is connected to the +B ter 15 the plate circuit of tube 4 to the oscillator grid
circuit. The coupling means may be an ex
minal through output load resistor I 3. The third
or suppressor grid I4 of tube 4 may be connected
' ternal reactance, or it may be provided by the
distributed capacity between the pickup plates
to grounded lead 9. A suitable bypass condenser
I and 2 as well as the inter-electrode capacity
9" is connected to ground from the energizing
within the tube.
lead feeding the anode I 0 and plate II. Con
In general, the operation of the system is
ldenser I 0’ connects the junction of coil L2 and
such as to- develop across load resistor I3 a signal
resistor I3 to ground. Condenser I0’ establishes
voltage representative of the displacement of
the lower end of coil L2 at ground potential
electrode 3. Where the latter is actuated by a
for high frequency currents, and has a relatively
high impedance to audio frequency currents.
25 stylus scanning the grooves of a sound record,
there will be developed across resistor I3 ampli
The cathode 5, grid 1 and electrode I IJ of tube
ñed audio frequency voltage corresponding to
4 provide the oscillator section of the system.
the recorded sound. Variation of capacities of
The positive cold electrode I0 is connected to
condensers I, 3 and 3, 2 changes the tuning of
the lower end of coil LI through direct current
blocking condenser I5. Electrode I0 is, there 30 the tuned circuitSLI-L 3 and L2-2, 3 with
respect to each other. If the plate circuit L2-2,
fore, the oscillator anode. Coil LI is resonated
3 and oscillator grid circuit LI--I, 3 were tuned
to a mean, or center, frequency Fc. This mean
to a common frequency, plate voltage would be
frequency is to be deviated in accordance with
fed back to `grid 1 in phase quadrature with the
the amplitude of the modulation frequencies.
The mean frequency of the oscillator may be 35 oscillator grid voltage. The feedback occurs, of
course, through path I1. If, however, the two
chosen from a range of 20 to 60 megacycles (mc.) .
resonant circuits are not tuned to a common
The deviation range of the mean frequency is
frequency, the plate voltage will be fed back to
dependent on the capacity change and the mean
oscillator grid 1 at a phase angle greater or less
frequency employed. A deviation up to about 1%
of the mean frequency could be employed, but it 40 than 90 degrees depending on the sense of de
tuning. AS a result of this feedback voltage the
oscillator voltage will be dependent upon the rela
sum of the oscillator deviation and the discrimi
tive tunings of the two resonant circuits. Since
nator resonance peak deviation. The choice of
the oscillator grid bias depends upon the am
the mean frequency of the oscillator is dependent
plitude of oscillations, the plate current of tube
on the sensitivity that is required from the pickup
4 is also dependent on the relative detuning of
device. Since the capacity changeQdue to vi
the two tuned circuits. Hence, the variable plate
bration, is of constant range as compared to the`
current develops a variable voltage across re
amount of deflection, then the higher the fre
sistor I3 which is a measure of the motion of
quency the >more this given capacity change will
mobile electrode 3.
produce a .frequency swing. Therefore, the
While the invention is in no way limited or
mean frequency should be as high as possible,
restricted to actual constants, the following are
and yet not too high to be unstable. In other
should be noted that this total deviation is the
Words, the distributed capacity of the coils is
likely to be less at thevhigher frequencies. My
invention is entirely independent of specific fre
supplied by way of illustration:
Resistance of resistor I6=18.000 ohms
Resistance of resistor 9’=4’1,000 ohms
4 quencies disclosed herein.
Resistance of resistor I 3=100,000 ohms
' It will be understood that in accordance with
Capacity of condenser 8:27 micro microfarads
my present method the condenser I, 3 is con
(mmf.)
nected across the oscillator coil LI, while the.
Capacity of condenser I5=120 mmf.
condenser 3. 2 is shunted across the discriminator 60 Capacity of condenser I0’=33 mmf.
coil L2. The discriminator coil should be slight
Inductance of coil LI=20 turns at 30 mc.
ly off tune from the oscillator mean frequency
Inductance of coil L2=20 turns at 30 mc.
Fc. either above or below. For example, the os
cillator mean frequency, as shown in Fig. 2, may
be below the discriminator coil peak resonance
frequency. The amount of off tune depends on
the "Q” of the discriminator resonance, which
is the slope of the two sides of the peak. The
oscillator mean frequency Fc should be located at
a fairl"7 linear part of the discriminator curve
side. The maximum frequency deviation could
be as high as 120 kilocycles (kc.) on either side
of Fc. The generic expression "angle modu
lated ” is used herein to designate that the modu
lation of the high frequency oscillations may
Considering more specifically the electrical re
lations existing in the present system, it is pointed
out that the locally-produced oscillations of 26
mc. are both frequency modulated and amplitude
modulated. In my present system I utilize the
fact that due to the non-linear action of the
oscillator, the plate current 0f tube 4 Will contain
an audio frequency component. It is the voltage
fed back through coupling path I1 which ampli
tude modulates the high frequency oscillations.
However, it is the frequency modulating of the
oscillations which causes the plate circuit L2-2,
anaozs
5
At coil L2 the stray capacity of the wiringl must
be considered part of the tuning capacity.
It is4 pointed out, furthermore, thatr either of
3 to develop a voltage whose magnitude and phase
are variable and depend on the oscillator fre
quency. The oscillator section excites the plate
resonant circuit by virtue of electron coupling
within the tube. When the high frequency plate
current flows through its resonant circuit, the
voltage developed thereacross depends upon what
the oscillator frequency is at that moment with
respect to the frequency of resonance of the
resonant plate circuit. It will be obvious, there
fore, that wide changes in phase and magnitude
of the high frequency plate voltage will be de
veloped because of the push-pull detuning of the
the fixed electrodes I or~ 2 may be removed there
by to provide single-sided operation. If the asso
ciated wire is removed, a ñxed capacitor should
replace the stray capacities which would be ab
sent. In the case of single-sidedy operation the.
general operation will be the same, except that
10y the variations in phase and magnitude of the
oscillator tank circuit and the plate resonant cir
high frequency voltage across coil L2 will not be
as great as in the case of push-pull operation.
While I have indicated and described a system
for carrying my invention into effect, it will be
apparent‘to one skilled in the art that
tion is by no means limited .to the
direction the frequency of oscillation is varied.
organization shown and described, but
Concurrently the frequency of the plate resonant
modifications may be made without
circuit is changed in an opposite sense thereby
from the scope of my invention.
causing the high frequency voltage across L2 to
What I claim is:
change to a degree determined by both of the 20
cuit.
As the mobile electrode 3 moves in one
said changes.
my inven
particular
that many
departing
.
-
l. In combination, a tube provided with an
oscillator section and an output electrode, means
Since there exists coupling between the two
connected -to said oscillator section to provide
resonant circuits (and this coupling may be
angle modulated oscillations which have a pre
capacitative, inductive, resistive or space charge)
determined mean frequency, a'resonant circuit
voltage is fed back from coil L2 to the oscillator
coupled to said output electrode, electron cou
grid v`I. There is, therefore, produced a secondary
pling between said oscillator section and said
change in oscillator frequency and amplitude due
output electrode developing said angle modulated
to this feedback voltage. This secondary change
oscillations in the circuit connected to said output
in amplitude of oscillation affects the plate cur
rent flow in the tube, and produces an audio fre 30 electrode, said resonant circuit being tuned to a
frequency different from said mean frequency by
quency voltage across the load resistor I3. It
a predetermined value, means responsive to op
may, also, be said that the leaky grid condenser,
network in the circuit of the oscillator grid func
eration of saidrfirst-named means for providing
frequency changes at the output electrode reso
tions to provide grid-leak detection of amplitude
nant circuit, a feedback coupling from the reso
modulated oscillations. At the same time the .
tube acts as a pentode amplifier for the audio
nant output circuit to said oscillator section, and
frequency >voltage developed across resistor I3.
resistive means in circuit with the output elec
trode for developing a Voltage representative of
and which voltage was caused by the changes in
plate current due to the variations in oscillator
theV said angle modulation.
grid bias which was in turn caused by the feed 40
2. In combination, a tube provided with an
back voltage.
oscillator section'and a positive output electrode,
The feedback through capacity I1 changes the
transducer means connected to said oscillator
amplitude of radio frequency oscillation at an
section to provide frequency modulated oscilla
audio frequency rate This is amplitude modula
tions which have a predetermined mean fre
tion. Because the amplitude of the radio fre 45 quency, a resonant circuit coupled toxsaid output
quency oscillation changes at an audio rate, the .
electrode, electron coupling between said oscilla
tor section and said output electrode developing
grid current, and hence the grid voltage, will have
oscillations in the circuit connected to said output
an audio component. The grid, therefore, has
electrode, said resonant circuit being tuned to a
a radio frequency voltage, an audio voltage, and
a direct current voltage applied to it. The direct 50 frequency different from said mean frequency, a
second transducer means responsive to operation
current voltage serves as a bias for the tube. The
of said first-named transducer means for pro
radio frequency voltage and audio voltage are
viding changes in tuning of said resonant output
amplified in the tube, and appear across the im»
circuit, a capacity feedback path coupling the
pedances in the plate and screen circuits. The
output electrode to said oscillator section, and an
plate tank consisting of L2 and stray capacities
audio frequency voltage output resistor in circuit`
has appreciable impedance only at the radio fre
with the output electrode.
quency, so only the radio frequency voltage ap
3. In combination, a tube provided with an»
pears across it. The resistor I3 is bypassed for
radio frequency so only the audio voltage appears
oscillator section and an output electrode, means
across it. When an amplitude modulated radio 60 connected to said oscillator section to provide
modulated oscillations which have a predeter
frequency voltage is applied to a grid-leak de
mined mean frequency, a resonant circuit coupled
tector, the grid circuit acts exactly as a diode
to said output electrode, coupling between said
detector thereby resulting in the detected audio
oscillator section and said output electrode de
voltage being present between grid and cathode
of the tube. This voltage is amplified by the 65 veloping said modulated oscillations in the cir
cuit connected to said output electrode, means
tube, and appears in the plate circuit. The en
responsive to operation of said first-named means
tire processI is called grid-leak detection.
In practice, the major portion of the tuning
capacity for coil LI is contributed by stray
capacitance's, and especially that of the leads- "`
.from the _oscillator section to the pickup pathï,
Merely by way of illustration, it is pointed out
for providing frequency changes at the output
electrode resonant circuit, a feedback path from
the resonant output circuit to said oscillator
section, and means in circuit with the output
electrode for developing a voltage representative
that in an average pickup the capacity between
pickup electrodes is about 0.25 mmf., while the
of the said modulation.
capacity between wires is of the order of 10 mmf.
oscillator section and a positive output electrode,
,
4. In combination, a tube provided with an
@412,023
7
8
transducer means connected to said oscillator
4frequencyV output resistor in circuit with'the out-`
section to provide frequency modulated oscil
put~ electrode.
lationsv which have a predetermined mean fre
quency, ‘a resonant circuit coupled to said out
put electrode, coupling between said oscillator
section and said output electrode for developing
oscillations in the circuit connected to said out
put electrode, a feedback path coupling the out
put electrode to said oscillator section, and an
audio frequency output resistor in circuit with 10
'
f
v
- 7. In combination,l in a system for reproducingÀ
records,'a tube provided with an oscillator section
and an output electrode, said oscillator section
having a grid andanode electrode,~means con-_
nected to said oscillator section grid to provide
frequency modulated oscillations which have a
predetermined mean- frequency, a resonant cir-¿
cuit coupled to said -output electrode, electron
coupling between said oscillator section 'and said
5. In a sound record reproducer system, a tube
output electrode for developing said‘frequency
provided with an -oscillator section and an out
modulated oscillationsin the circuit connected
putele'ct‘rode, means'connectedvto said oscillator'
to said output electrode, said resonant circuit
section `to provide angle modulated oscillations 15 being tuned to a frequency different from said
the output electrode.
~
which have a predetermined mean frequency, a
mean frequency-by a predetermined value, means
resonant circuit coupled to said output electrode,
electron coupling between said oscillator section
and said output electrode for developing said
responsive to operation of said first-named means
for providing frequency changes at the output
records, a tube provided with an oscillator section
frequency of the order of 26 megacycles, a reso
electrode resonant circuit, a feedback coupling
angle modulated oscillations inthe circuit'con 20 from the resonant output circuit to said oscilla
tor grid, grid leak detection means in circuit with
necte'd to said output electrode, said resonant
circuit being tuned to a frequency different from
said oscillator grid, and resistive means in cir
said mean frequency by a predetermined value,
cuit with the output electrode resonant circuit
for developing an audio frequency voltage repre
a feedback coupling from the resonant output
circuit to said oscillator section, grid-leak detec
sentative of the said modulation.
tion means in circuit with the oscillator section
8. In combination, a tube provided with an
oscillator section and a positive output electrode,
grid, and resistive means in. circuit with the out
put electrode for developing a voltage representa
a ñrst capacity pickup device connected to said
tive of the said modulation.
_oscillator section to provide frequency modulated
I,oscillations which have a predetermined mean
6. In combination in a reproducer of sound
and a positive output electrode, capacity pickup
nant circuit coupled to said output electrode, elec
tron coupling between said oscillator section `and
provide frequency modulated oscillations which
said output electrode developing oscillations in
have. a predetermined mean„ frequency, a reso
the circuit connected to said output electrode,
nant circuit coupled to said output electrode, elec
said resonant circuit being tuned to a frequency
tron coupling between said oscillator section andY
of the order of 26.1 megacycles, a second capacity
said output electrode for developing oscillations
pickup device responsive to operation of said first
named pickup device for providing opposite
in the circuit connected to said output electrode,
said resonant circuit being tuned toa frequency 40 changesl in tuning of resonant output circuit, a
capacity feedback path coupling the output elec
different from said mean frequency, a second
capacity pickup means responsive to operation
trode to said oscillator section, and an audio
of u'said ñrstenamed pickup means for providing
frequency output resistor in circuit with the out
put electrode.
‘
changes in tuning of said resonant output circuit,
a capacity feedback path coupling the output
HARRY J. WOLL.
electrode to said oscillator section, and an audio
means connected to said oscillator section to
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