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Патент USA US2570705

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Oct. 9, 1951
5 Sheets-Sheet l
Filed Feb. 13, 1946
E1 2:1
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Oct. 9, 1951
Filed Feb. 13, 1946
5 Sheets-Sheet 2
M THa/p’bi/n/
OCt- 9, 1951
Filed Feb. 13, 1946
5 Sheets-Sheet 4
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Oct- 9, 1951
Filed Feb. 13, 1946
5 Sheets-Sheet 5 '
Patented Oct. 9, 1951
Marie-Thérese Martin, Versailles, France
Application February 13, 1946, Serial No. 647,291
~ In France March 31, 1942
Section 1, Public Law 690, August 8, 1946
Patent expires March 31, 1962
' 40mins.
(01. 179-171) _
selecting arrangement making it possible to select
secondary windings of which are inserted into the
grid circuit of a triode valve connected to the
and adjust at will the harmonics of a simple-or
ampli?er arranged before the loud-speaker.
speaker, after ampli?cation, sounds, the quality or
In particular, when a number of oscillators are
utilised, the latter are either each connected to
the ampli?er by a selector arrangement similar
to that described, or, if they are mounted in par
allel or in series, are connected to the amplifier
by a single selector arrangement.
When several selector groups are used, each
group constituting a‘ selecting arrangement con
“timbre” of which is exactly determined;
structed according to the invention and compris
ing one or more transformers, may be provided
for a de?nite number of musical notes. The as
The present invention relates to a harmonic
alternating‘ ‘current,
emanating, for example, from one 'or'more low;
frequency oscillators.
This selection of harmonics and adjustment of
their relative amplitudes renders it possible to
receive, at the output end of the apparatus'low-v
frequency’ current's'which" produce in‘"a~'loud
harmonic-selecting arrangement
function just as; easily in the case when it is sup
plied with a single alternating current of de?nite
frequency as when it is supplied with a variety
15 semblage of grorps thus makes it possible to cover
one or more octaves. >
of currents of diverse frequencies, of approxi
The harmonic-selecting arrangement accord
mately the same or widely different values, with
out the fact of the coexistence of these frequen
cies producing interference of troublesome‘ in
ing to the invention is also characterised by the
feature that each of the transformers constitut
20 ing the chain comprises a primary coupling wind
ing connected to the circuit of the oscillator, a
secondary winding inserted between the earth or
mass and the grid of the valve previously men
tioned, and ?nally an auxiliary winding the func
currents which, after passing through an am‘ 25 tion of which is to eliminate undesirable fre—
quencies, interferences etc. The windings of
pli?er, arecapable of producing in a loud-speaker
the various successive transformers for coupling
sounds similar to those produced by one‘ or’more
with the oscillator and the windings for connec
musical instruments, ‘ determined ‘ in advance,
tion to the valve grids are respectively mounted
playing together or separately, ‘according to: any
30 in series.
The invention also concerns the constitution
Thus 'the'said arrangement makes it possible,
of the transformers of harmonic-selectors, and
among other applications, to constitute an elec
is characterised by constructional features such
tric organ, comprising on the one hand a certain
as the following, given by wav of example: the
number of oscillators of any kind‘controlled'by
one or more keyboards, together with the said 35 magnetic circuit of all or of certain of the trans
The apparatusmakes it possible to obtain, ‘from
a Simple altemti?gfcurmnt Qrl'fmm a number
of alternating currents‘ of diverse'frequencies,
arrangement, and ?nally one or more ampli?ers
followed by loud-speakers. The harmonic-se
lecting arrangement is then connected to con
tact-making switches each bearingan indication
relating to some de?nite organ Step. By acting
formers is either open. partially open or totally
closed, according to the result desired. This
magnetic circuit is constituted according to cir
curcstances by laminated iron strips or else‘ by
40 solid iron, or by any other magnetic material: the
on these switches'as upo'n‘thestops of a pipe
magnetic coupling of the windings is more or
organ of standard construction, ‘the performer
less tight according to their function: and the
is able' to ‘choose whichever stop or‘ ‘stops he
characteristics of the winding of the coils are se
lected according to the purpose in View in the
The apparatus makes it possible in addition to 45 particular usage of each of the transformers.
In agreement with the principle of construc
produce new'musical instruments, controlled by
tion according to the invention, the winding of
keyboards‘ or‘ by ‘ any other means. "The tone
each of the transformers connected to the valve
qualities of these instruments may be new or may
grid is provided with a shunt circuit comprising:
correspond to those of known instruments.
The harmoniclselecting'device according to the
invention, interposed between'an oscillator and
a sound-output meansfsuch as a loud-‘speakerfis
50 on one hand, a switch making it possible to short
circuit the winding. it being possible to actuate
this switch separately or at the same time as
each of the switches similarly mounted in the
shunt circuits of the other transformers, and,
capable of being shortecircuited'individuallyythe 55 on the other hand, condensers, resistances, in
characterised by'the ‘usev of a chain ‘or transform
ers,'identical or different, coupled in ‘series; and
ductances or combinations of these elements,
making it possible to determine the characteris
tics of the shunt circuit, and thus to effect con
trol of the same, and to carry out any desired
regulation of the relative proportions of the
The invention also concerns improvements in
the circuit connections of the control elements
windings connected to the grid makes it possible
to obtain varied and different tone qualities.
Figure 11 is a circuit diagram of apparatus
comprising several harmonic-selecting arrange
ments constructed according to the invention.
Figures 12, 13 and 14 show the utilisation of
the harmonic-selecting arrangement according
’ vto the invention for eifecting control of the low
frequencycurrent produced by oscillators of var
characterised by the possibility of putting one or 10 ious types.
In thediagram of harmonic-selector shown in
more or all of the control elements into or out
Figure 1 it will be seen that in agreement
of action, or again of putting the transformer
with the invention, a chain of transformers
itself out of service by shortecircuiting its wind
mentioned above, these improvements being
ing, this being carried out at will and as re
T1, T2 . . . Tn, is interposed between an oscil~
quired by the simple control of switches suitably
arranged, thus making it possible at any instant
to obtain the musical tone and volume required.
According to the invention, improvements
identical in principle with those just described
lator E1 and an amplifier A mounted in front of
a loud-speaker, such as a loud-speaker, not
are applicable to the shunt circuit of the aux
iliary transformer winding provided for the
elimination of undesirable frequencies and inter
shown, the secondary windings I1 of these trans
formers being coupled in series.
The oscillator E1 may be of any conventional
type suitable for the purpose of generating com
plex electric oscillations of musical frequencies,
and may be for example be of the construction
described in the ampli?er is likewise conven
Finally the invention extends to methods of
tional in character as used for instance in radio
realisation and utilisation of harmonic-selecting
arrangements characterised by the feature that
the oscillators producing the alternating supply
construction. Neither of the elements E1 and A
form any part of this invention.
similar frequencies are applied to the apparatus.
All the primary windings I2 are connected in
Each of these transformers comprises on an
iron core,'which may‘ be either open or partially
current may be of any kind, for instance, micro
phones, vibration-scanning devices, or else acous
or completely closed as more fully described here~
tic resonators connected with a musical instru 30 inafter in connection with Figs. 2. 4, and 6, in
ment, acting on the vibration-scanning devices
addition to the secondary winding 11, a winding
connected to the harmonic-selecting arrange
I2 connected in the circuit of the oscillator E1,
ment, permitting in the latter case the modi?ca~
and an independent winding I3 the function of
tion or ampli?cation as may be desired of the
which is to attenuate or eliminate interferences
natural sound of one or more musical instru
which may be produced when several currents of
Other characteristics will appear from the
detailed description which follows.
series in the circuit of the oscillator E1.
All the secondary windings I1 are likewise con
nected in series, one of their extremities being
connected to earth and the other extremity to
the grid g of a three-electrode valve, the plate
current of which is led to the ampli?er A, through.
arrangement according to the invention.
45 a connecting condenser K. A high-tension.
current is applied, passing through a resistance r
Figure 2 is an example of construction of a
on the connection between the valve plate p
transformer with open circuit used in a har
and the condenser K.
monic-selecting arrangement.
Each winding I1 of the various transformers
Figure 3 is a circuit diagram of the transformer
The accompanying drawings, given solely by
way of example, show diagrammatically forms
of construction and circuit connections of har
monic-selecting devices or groups of devices in
agreement with the invention.
Figure 1 is a diagram of a harmonic-selecting
according to Figure 2.
Figure 4 is another example of construction ofv
is mounted a switch $1, $2 . . . can when this
an open-circuit transformer.
Figure 5 is a circuit diagram of a transformer
switch is closed the corresponding transformer
is shunted and thus put out of action.
comprises a shunt circuit s, s1 . . . s", in which
constructed according to Figure 4.
Condensers, resistances, inductances or com
Figure 6 is an example of construction of a 55 binations of these elements denoted by 01, d1, 02,
closed-circuit transformer.
Figure '7 shows a method of assembling the
d2 . . . c", d" are connected respectively in the
circuits of the windings I1 and I3 of each trans
various elements of a selecting arrangement on
former to modify their characteristics and to
a single chassis or supporting frame.
carry out any desired proportioning of the har
Figure 8_ is a circuit diagram of a transformer 60
monics. In addition, the cathode Ca of the
for a selecting arrangement in which the circuit
valve L1 is earthed through the medium of a sys
shunting the winding connected to the valve grid
tem comprising a resistance and a polarisation
comprises several electric or magnetic elements‘
condenser R.
which can be put into action separately or put
The transformers T1, T2 . . . Tn may be alike
out of action simultaneously.
or different according to requirements. In gen
Figure 9 is another example of a transformer
eral they are selected with different character
circuit in which the shunt circuit of the aux
istics, and a de?nite part is assigned to each.
iliary winding provided for the elimination of
The various circuits of these transformers are
undesirable frequencies or interference com
prises adjustable electrical control elements.
70 so adjusted as to obtain the required relative
strengths of» the harmonics. The windings I‘
Figure 10 is a general example of assembly of
and I3 are tuned by means of condensers, resist
a selecting arrangement according ‘to the inven
ances, inductances or other elements denoted by'
tion in which the putting into or out of action
at will of one or more of the various control ele
ments of the shunting circuit of the trans?qlimeli
c1, d1, etc., and render it possible to modify the:
characteristics Qt these windings as to obtain
an exact» regulation of the selected harmonics‘.
By proceeding in this way to-the'extreme limit it
isipossible so to tune the circuits as to suppress
ail harmonics, leaving only the fundamentals.
The system of coupling windings F connected
Figure 6' shows a transformer of the closed
circuit type, the magnetic circuit N of which
has the form of two E’s joined by their limbs.
The frame B carrying the primary and auxiliary
windings I2 and I3 wound one over the other,
and the frame C carrying the secondary wind
11, are mounted side by side on the central
limb of the magnetic circuit. The electric cir
As has been explained above, by positively con
cuit diagram of this transformer is similar to
trolling the switches 1'1, :c'z . . . 13'" it is possible
that given in Figure 3.
to short-circuit and consequently put out of ac
It is possible without going outside the ambit
tion one or more of ‘the transformers, thus mak
of the invention to modify the arrangement of
ing it possible to eliminate the harmonics to
the windings, to increase their number ‘and to
which each transformer or group of transformers
choose any possible form or constitution of the
is related.
15' magnetic circuit.
in series preferably possesses a very low imped
Figure 2 shows an example of realisation of a
When the harmonic-selector is part of a com
transformer for a selecting arrangement accord
ing to the invention. The~ transformer" shown is
of the open magnetic circuit type. It comprises a
plex electrical musical. instrument, such for ex
ample as ‘an electric organ, it is convenient to
group all the elements on a single chassis or ‘sup
20 porting frame.
Figure '7 shows an example of this. In this
figure the selecting transformers T1 and T2 con
reference A, upon which are mounted two frames
stituting the chain previously de?ned are ?xed
B and C. The frame B carries‘ the primary wind
on a chassis F, which in its turn is mounted
ing 1’, which is connected to the oscillator, and
upon. which is wound the auxiliary winding I3, 25 on a base plate G. The transformer T1 is of
the closed type and carries the coils B1 and C1;
provided for the purpose of reducing interference
whereas the transformer T2 is of the open type
and undesirable frequencies. The windings I:
core N formed by a bundle of laminated rec
tangular iron strips generally indicated by the
and‘ I3 are thus close coupled. The frame C car
ries the secondary winding I1, which is connect
ed on the one hand to earth, and on the other
hand’ to the grid of the triode valve preceding the
ampli?er. This secondary winding I1 is coupled
less tightly than the winding Is to the primary
winding I2, which is found to be advantageous.
The electric circuit connections of such a
and carries the coils‘ B2 and C2. The control
elements of the windings are contained in the
base G, upon which is mounted a multiple-elec
trode valve L.
On the upper part of the chassis, a strip H
of insulating material carries a series of con
necting terminals cl, (:2, c3, c4 . . . , to which
are connected the windings of the coils B1, C1,
C2, the control elements, and the valve L.
A plug D enables the selector system thus con
stituted to be branched between the oscillation
transformer are given inv Figure 3, in which are
shown: the core N, the secondary winding I1,
connected on the one hand to the grid L1 and.
generator and the ampli?er connected to the
on the‘ other hand to earth (or more frequently 40 loud-speaker. A selector group like that de
scribed is provided for example for a range of
inserted between other‘ secondaries or other se
n successive notes. It is then repeated by a
l‘ector‘ transformers‘ ‘connected in series between
similar system for the following n notes, and
the grid’ and earth) and comprising a shunt cir
so on. A suitable number of such selector groups
cuit S‘ in' which is mounted a switch X, making it
possible to put out of action, when it is closed,
renders it possible in this way to cover the re
quired number of octaves.
Figure 8 shows diagrammatically an example
the primary winding I2 connected in the circuit
of the circuit connections of the various control
of an oscillator E1; and: the auxiliary winding
elements of the secondary circuit of a selector
Is, in the circuit of which are connected control 50 transformer. The secondary winding 11 of the
elements d1.
transformer, connected to the grid 9 of the valve
The transformer shown in Figure 4 is of the
and to earth, is provided with a shunt circuit
the transformer and the control elements 01;
open-circuit type as» in the preceding case, but
it has two separate secondary windings which
in which are mounted in parallel various con
trol elements, namely: a condenser cl, a con
are‘ connected in series to the grid of the valve. 55 denser c2 of different value from the preceding,
an‘ inductance Z connected in series with a con
The core N is constituted by an assembly of. lami
denser c3, a resistance H, and a resistance r2
nated iron strips. The frame B, mounted on the
connected in series with a condenser 04. All
core N’, carries the primary and auxiliary wind
these elements" are connected to the contact
ings I: and Is. on either side of the frame B are
mounted on‘ the core‘ N two frames C1 and 02, 60 studs of a revolving contact switch X1, the last
stud s being connected directly to the output
each carrying a secondary winding I1 and l'i
of the winding I’. The movable brush of the
respectively, with similar or different char
switch XI is connected to the input of the wind
acteristics as the case may be.
ing I’. By controlling the switch X1, one of the
Figure 5 shows the electric circuit connections 675 control. elements cl, c2, (:3, Z etc. is put into or
of such a transformer. The circuits in and s’i
out of action, and the characteristics of the
shunting the secondary windings I1 and I~'1 each
oscillation applied to the grid g are thus modi
comprise a switch X1. and X’i, making it possible
fled. When the brush is placed on the stud S,
to put into or out of action the corresponding
the transformer is short-circuited and thus put
winding and control elements or and c’i, which
out of action, and no oscillation is transmitted.
may be different or similar. There has thus been
A similar control may be applied to the trans
in. fact provided a system capable of replacing to
former winding intended to eliminate interfer
ence or undesirable frequencies, to the terminals
a certain extent a group of two transformers, the
of which. are branched the control elements, ad
windings‘ of which connected to the grid are in
justable: or not, as required.
A diagrammatic
example of circuit connection is shown in Figure
9. The shunt circuit of the auxiliary winding I3
of the transformer comprises a condenser c and
a variable resistance r. The adjustment of the
resistance 7* makes it possible to modify the ac
tion of the winding I3.
It should be noted that for all the selector
dependent'oscillators, each of these maybe con-q
nected to a harmonic-selector which issuited to’
it. Figure 11 shows an arrangement of this type
in which several oscillators E1, E2, En are used,‘
each branched on a chain of harmonic-selector
circuits C1, C2,-Cn respectively. These arrange
ments C1, C2, C11, are each constituted by a chain
of transformers as previously described, the'se'c
ondary windings of which act on the-grids g1,
tem', it is often an advantage to control simul
taneously, by the same mechanical means, all 10 g2, g" respectively of triode valves. The cathode}
the resistances such as r with which the trans
of each of the valves is connected to earth
formers in question are provided.
through the medium of a unit comprising a re~,
The methods of control and regulation de
sistance and a polarisation condenser R, and
the plate circuit of each valve is connected
scribed above give rise to many combinations,
which fall within the scope of the invention.
through the medium of a condenser K to the
The variety of tone qualities, the extent of the
input of an ampli?er A acting upon the sound-,
output apparatus, such as a loud-speaker. A’
musical range controlled, and the power of emis
transformers of the same rank, on the same sys
sion may advantageously be as great as possible,
high-tension source HT supplies the plate of
each 'valve through a resistance r.
and a good result is obtained by judiciously se
The modulatedv current arriving at the ampli
lecting the number and characteristics of the 20
?er is thus represented by the group of alternat-'
transformers and of the control elements.
Simple and satisfactory harmonic-selecting sys
ing currents produced in the valves L1, L2, Ln,
tems can thus be obtained.
under the modulating action impressed ‘on the
An example of combined circuit connection is
shown diagrammatically in Figure 10, in which
the selecting transformers T and T’ have their
secondary windings I1 and P1 connected in series,
and connected on the one hand to the grid g of
grid by the current emanating from the oscil-'
lators after selection of the harmonics in the
chains of transformers.
The number of transformers in each chain
can be chosen at will, so it can easily be seen
that it is possible to carry the selection of»
the valve L and on the other hand to earth. The
shunt circuit of the winding 11 is constituted by 30. harmonics as far as may be required and indeed
the connection according to a particular ar
the latter may be eliminated to any desired
extent, even completely, leaving only the funda-,
rangement of condensers cl, c2, c3, of a resist
ance rl, an inductance Z and switches Xi, X2,
X3, X4, X5. In similar fashion, the shunt cir
cuit of the winding I'1 comprises the condensers
c4, 05, the resistance 12, and the switches X6,
X1, X8.
Byway of example, in the practical applic_a—,
tion of the invention to the construction of an‘
electric organ, the set of contact-making switches
It can be seen at once that if the switches are
controlling the shunt circuits of the transformers
selecting the harmonics in all the chains maybe
closed (except X5) the transformers are both
short-circuited, and no oscillation is transmitted
to the valve L, and the loud-speaker emits no
connected in any desired combination to'con
trolling members, such as organ stops, enabling
the performer to operate these switches either
individually or in various groups at will.
If the switches X2 and X5 are kept open, the
condenser cl and the resistance 1! are put in
circuit. 'A sweet or mellow tone is obtained,
like that of the bourdon stop of an organ.
If X4 and X5 are opened, the condenser 02
is in circuit and the note becomes richer or
stronger, like that of a ?ute stop.
If X3 and X5 are open the condenser cl alone
is in circuit, and it is chosen in such a way that
the timbre is richer or stronger than in the
preceding case.
The simultaneous opening of X3 and X4, with
X5 still remaining open, gives another flute-like
tone quality and similarly, the combined manipu
lation of the two switches X3 and X4 conveys
to the ear the impression of several ?ute stops.
If again the switches XI and X5 are open,
this way it is possible to put into or out of action,
as previously described, one or other of the chains
of transformers of the selecting apparatus, any
particular transformerin each of the chains, or
any control element for the shunt circuit of each
transformer, regulating in this way at each
moment the timbre, the quality and the power
of the resultant sound emitted.
It is possible to conceive a musical instrument
divided up into groups of a certain number of
notes, each group acting on one of the micro
phones ‘used, which is connected to a selector
group contained in the harmonic-selecting ap
paratus and designed to‘ synchronise with the
notes selected.
' ~
In Figure 13 the oscillations are transmitted to
the selector S by a series of vibration-reading-or
the winding I1, being shunted only by its own 60 scanning devices L1, L2, L11 etc., which may be
electro-magnetic, electrostatic, electro-dynamic,
capacitance, transmits the higher harmonics,
giving a sound like that of a trumpet stop.
piezo-electric, or of any'other type.
Finally, the closing of the switch X5 consider
As shown in Figure 14, the oscillations received
ably modi?es the timbre obtained by the
may also emanate from selective sound resona
manipulations just described, so that in this 65 tors R1, R2, R71. etc. Theyare transformed into
case the tone of several different musical instru
ments can be obtained, such as the oboe, octave
?ute (?fe or piccolo) etc.
electrical oscillations by the systems T1, T2, Tn
and then transmitted to the suitably tuned
groups of the harmonic-selector S.
An arrangement constructed in accordance
In similar fashion, the combined manipulations
of the switches controlling the shunt circuit 70 with ‘the latter conditions and placed beside a
of the winding I1 make it possible to increase
musical instrument modi?es the sound produced,
the variety of tone qualities and the range of
the timbre‘ and intensity of which’can be ad
pitch of the selector.
iusted' at will.
When the low-frequency alternating current
, In order to serve as a guide to the circuit
to be controlled is supplied by a number of in 75 values of the various elements of the apparatus,
the following values are given by way of exam=
ple for the arrangement shown in Figure 10.
3.1m an electronic musical instrument, av har
monic selecting device, comprising in combina
The valve is a 636, the cathode of which is
tion, a thermionic valve, a chain of audio fre
earthed “through a resistance of 2,000 ohms
shunted by a condenser having a capacity of 10
Imicrofarad's. The plate circuit of this valve is
connected to the high tension positive pole
duency transformers havingv the primary wind
ings thereof connected in series for connection to
a source of audio frequency alternating electric
current, said transformers having their secondary
windings connected in series to the control elec
trode of the thermionic valve, shunt circuits con—
through a resistance of 250,000 ohms, and the
coupling condenser may have a capacity between
0.005 and 0.5 microfarad.
nected across the secondary windings of the re~
7 The transformer T has a core of the shape
spective transformers, each shunt circuit in
cluding at least one tuning element for modify
shown in Figure 2, the inductance of the respec—
tive windings I2, I3, I1 being 0.00015, 1.24 and
4.36 henries.
ing the transformer characteristic, auxiliary at
tenuating circuits including windings coupled to
The transformer '1" has a core of
the shape shown in Figure 0, the inductance of
the windings of the respective transformers for
the respective windings 1'2, 1'3 and I'i being
eliminating undesired frequencies, and switch
0.0014, 11.9 and 29.7 henries.
means for selectively short-circuiting said sec
The value of the inductance Z is 3 henries and
ondary windings to enable one or more trans
the resistances R2, R3 have a value of 10,000 ohms.
formers in the chain to be instantly put out of
The capacity of the condenser connected to the
operation for regulating the harmonics trans
terminals of the winding 13 is 0.1 microfarad,
mitted to the control electrode of the thermionic
the capacity of the condenser connected to the
terminals of the winding I’3 being also 0.1 micro
4. In an electronic musical instrument, a har
monic selecting device, comprising in combina
The capacity of the condensers C1, C2, C“, C5
tion, a thermionic valve, a chain of audio fre»
lie between 0.002 and 0.25 microfarad, accord
quency transformers having the primary wind
ing to the acoustic frequency at which the ele
ings thereof connected in series for connection
ment is to operate. The capacity of the con
to a source of audio freduency alternatirrr elec
denser C3 lies between 0.005 and 0.03 microfarad
tric current, said transformers having the sec
More generally, the arrangement is capable of 30 ondary windings thereof connected in series to
modifying the timbre and volume of any sound
the control electrode of the thermionic valve, a
plurality of tuning elements connected to each
Numerous alternative arrangements can be
transformer secondary winding, switch means
carried out by applying the characteristics here
inbefore set forth without going outside the arm
bit of the invention.
for shunting said tuning elements selectively
across said secondary winding to modify the
transformer characteristic and regulate the har
monics transmitted to the control electrode of
I claim:
1. A harmonic selecting device, comprising in
the thermionic valve through the transformer,
auxiliary attenuating circuits including windings
coupled to the windings of the respective trans
formers for eliminating undesired frequencies,
combination, a thermionic valve, a chain of
audio-frequency transformers having the pri
mary windings thereof connected in series for
connection to a source of audio frequency alter
and switch means for selectively short-circuiting
nating electric current, said transformers having
said secondary windings to enable one or more
their secondary windings connected in series to
the control electrode of the thermionic valve,
switch means for selectively short-circuiting
said secondary windings to enable one or more
transformers in the chain to be instantly put out
transformers in the chain to be put out of action
for regulating the harmonics transmitted to the
control electrode of the thermionic valve through
the chain.
of operation, and auxiliary attenuating circuits
including windings coupled to the windings of
the respective transformers for eliminating un
desired frequencies.
2. A harmonic selecting device, comprising in
combination, a thermionic valve, a chain of audio
frequency transformers having the primary ‘
The following references are of record in the
?le of this patent:
windings thereof connected in series for connec
tion to a source of audio frequency alternating
current, each transformer having a secondary
winding loosely coupled to the primary Winding
thereof, the secondary windings of the respective
transformers connected in series to the control
electrode of the thermionic valve, switch means
for selectively short-circuiting said secondary
windings to enable one or more transformers in
Cahill __________ __ Feb. 25,
Kendall ________ __ Mar. 24,
Austin __________ __ Aug. 24,
Lansing __, ________ __ Feb. 2,
Kock ____________ __ Mar. 4,
Kock ____________ __ Aug. 31,
Botsford __________ __ Nov. 2,
Larsen ___________ __ July 2,
the chain to be instantly put out of operation,
and auxiliary attenuating circuits including
windings in close coupled relationship to the pri
mary windings of the respective transformers for
eliminating undesired frequencies.
France __________ __ Aug. 2, 1943
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