Improvements in Electric Telephonic Transmitting Apparatus.
Year: 1892

page_text: Date of Application, 15th Aug., 1892
Complete Specification Left, 15th May, 1893-Accepted, 17th June, 1893
PROVISIONAL SPECIFICATION.
Improvements in Electric Telephonic Transmitting Apparatus.
I, ALEXANDER MARR, of 9 Repton Street, Chorlton-on-Medlock, Manchester,
in the County of Lancaster, Electrical Engineer, do hereby declare the nature of
this invention to be as follows:-
In the telephonic transmitters to which this invention relates, the variable
resistance element consists of granulated carbon or inoxidisable material unalterable
by the hygroscopic conditions of the atmosphere and having a similar resistance to
that of carbon. The material preferred to be employed is granulated graphite
such as is produced in coke ovens and gas retorts, and as used for many years past
in the well known "Hunnings" and "Marr" instruments.
These improvements consist; (1), In the construction and arrangement of the
variable element containing cell and electrodes; (2), In arrangements for
periodically disturbing the granules of carbon and preventing their consolidation;
(3), In means for concentrating the sound waves of the voice upon the diaphragm ;
and (4), In the construction of the cores of the induction coils employed with the
transmitters.
In the variable element, the granulated carbon is arranged between two electrodes
of carbon or platinum, but preferably of carbon in the form of thin plates or discs,
and I prefer to construct and arrange these electrodes in such a manner that they
are not parallel with each other, and so that one part or point of one of the electrodes
approaches very closely to, without actually touching the other. The whole of the
variable element, consisting of the granulated material and the electrodes, may be
mounted in a containing cell attached to the back of the diaphragmn, in which case
I prefer to interpose between the cell and the diaphragm, a buffer which may
consist of a metallic spring or of metallic springs, or of a ring pad or cushion of
indiarubber, for the purpose of preventing the transmission to the cell of extraneous
shocks and vibrations. The cell may be formed of cardboard or ebonite, or it may
be constructed of brass or other suitable metal lined with an insulating material, the cell
being constructed in two parts connected together by means of internal and external
screw threads or otherwise. Or, the variable element cell may be formed in a fixed
backing containing the back electrode, in front of which and immediately adjacent
thereto, is the diaphragm, on which, or on a buffer on which, the front electrode is
mounted in such a manner as to close the front of the cell sufficiently to prevent
the escape of the granules. The cell, instead of being mounted or arranged con-
centrically with the diaphragm, may be mounted so that its lower portion covers
the centre of the diaphragm.
It is well known that in transmitters to which these improvements more
particularly relate, the granules of carbon gradually settle and interlock with each
other, thus reducing the efficiency of the instrument. To avoid this result I may
arrange to blow air periodically through the cell from a small pair of bellows
actuated by the switch, or I may arrange to shake, or disturb the cell each time
that the instrument is used. I prefer to adopt the latter course as being simpler,
and generally more efficacious. This mechanical shaking or disturbance of the cell
may obviously be effected in very many different ways; thus, when a magneto is
used with the instrument for signalling, the cell may be made rotary and be
geared with the pinion of the magneto, or it may be mounted upon the lever of the
switch upon which the receiver hangs when out of use, so that it is moved each
time the instrument is used. The method which I have found most convenient in
practice is to mount the cell and diaphragm in a comparatively small casing which

page_text: can slide vertically in guides. The transmitter thus mounted, is forced upwards by
a spring or springs of sufficient strength to keep the transmitter alone in the higher
position, but insufficient to do so when a weight is added. On the lower part of
the casing I secure a hook, upon which the receiver may be hung, so that when the
receiver is on the hook, the transmitter is pulled thereby into the lower position,
and when the receiver is removed, it is forced upwards by the spring. The move-
ment of the transmitter may in this case be conveniently employed to open and
close the circuits. Thus, when the transmitter is in the higher position, and in
use, two contact springs in the primary circuit press upon two contact points on
the transmitter and thus close the local circuit through the variable element.
In the same position of the transmitter, the main line contact spring is pushed
into contact with the contact spring of the speaking circuit. When the receiver
is hung up, and the transmitter thus pulled down, the local primary circuit through
the transmitter is opened, and the main line contact spring falls into pressure with the
contact spring of the ringing circuit. To effect this result more easily, the speaking
and ringing contacts are arranged vertically above and below the main line contact
spring, and the local circuit contacts are arranged one on each side of the centre.
For the purpose of concentrating the sound waves of the voice upon the
diaphragm, I may use a coned mouthpiece with a flange or annular projection
within the broad open end. This flange or projection may consist simply of an
indiarubber ring.
In order to avoid the inconveniences and losses arising from the present method
of constructing the cores of the induction coils used with telephonic transmitters, I
build up the cores from wires having approximate triangular or truncated
triangular cross sections, or such sections that when collected together they may
form a compact cylindrical body. Contact of these wires is prevented by any
suitable insulating medium such as paraffined paper or mica. If there be more
than one layer or ring of the wires, then each layer also is insulated. The core
may be tightened by driving a small conical wedge into the centre of each end.
A cheap bobbin and core may be constructed by placing flanges on the ends of
the core before tightening up with the conical wedges, the bore of the flanges being
of such a diameter that the conical wedges will expand the cores so as to fill the
bore tightly, and thereby fix the flanges.
Puted this 12th day of August. A D 1892
WILLIAM E. HEYS,
Agent for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Electric Telephonic Transmitting Apparatus.
I, ALEXANDER MARR, of 9 Repton Street, Chorlton-on-Medlock, Manchester
in the County of Lancaster, Electrical Engineer, do hereby declare the nature of
this invention, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
In the telephonic transmitters to which this invention relates, the variable
resistance element consists of granulated carbon or inoxidisable material unalterable
by the hygroscopic condition of the atmosphere and having a similar electric
resistance to that of carbon. The material preferred to be employed is granulated
graphite such as is produced in coke ovens and gas retorts, and used for many years
past in the well known "Hunnings" and "Marr" instruments.
These improvements consist:-(1) In the, construction and arrangement of the
variable resistance containing cell and electrodes. (2) In arrangements for
periodically disturbing the granules of carbon and preventing their consolidation.
(3) In means for concentrating the sound waves of the voice upon the diaphragm.
And (4) In the construction of the cores of the induction coils employed with the
transmitters.

page_text: Figure 15 is a section of another modified form of the cell.
Figure 16 is a perspective view, and
Figure 17 a transverse section of one end of the core for the induction coil.
Figure 18 is a vertical elevation of the receiver hook and circuit connections as
they exist when the instrument is in use.
Figure 19 is a similar elevation, the instrument being out of use.
Figures 20 and 21 are plans of the circuit connections corresponding with
Figures 18 and 19.
Figures 22, 23, and 24 are an elevation, end view, and partial section of the end
of the receiver hook.
In the variable element, the granulated carbon F is arranged between two
electrodes E E¹, of carbon or platinum, but preferably of carbon in the form of
thin plates or discs. I prefer to construct and arrange these electrodes in such a
manner that they are not parallel with each other, and so that one part or point of
one of the electrodes approaches more closely to, without actually touching the
other. Modified forms of this preferred construction of the electrodes are
illustrated by Figures 9 and 15. As shewn by Figure 9, the back electrode has a
projection or protuberance facing and nearly approaching the front electrode.
Figure 15, the back electrode has an inclined front surface, the upper part of which
approaches the front electrode. I do not limit myself however to the particular
forms illustrated.
In
The whole of the variable element, consisting of the granulated material and the
electrodes, may be mounted in a containing cell C¹ attached to the back of the
diaphragm D, (Figure 154) in which case I interpose between the cell C' and
the diaphragm D a buffer B₁ which may consist of a metallic spring or springs, but
which preferably consists of a ring pad or cushion of indiarubber, for the purpose of
preventing the transmission of extraneous shocks and vibrations. This cell may be
formed of ebonite or cardboard, or it may be constructed of brass or of other
suitable material lined with an insulating material. For convenience of access to
the interior, the cell may be constructed in two parts and the two parts may be
secured together by an external screw thread formed on one part, and an
internal corresponding thread formed on the other part.
Or, the variable element cell C¹ may be formed in or secured to a fixed backing
containing the back electrode in front of which and immediately adjacent thereto, is
the diaphragm D on which, or on a buffer on which, the front electrode is mounted
in such a manner as to close the front of the cell sufficiently to prevent the escape

page_text: of the granules F. This modification is illustrated by Figures 3, 9, 10, 12, and 15.
In Figures 3 and 9 the back electrode E¹ is let into a circular recess formed in the
base of the cell C¹. In Figures 10, 12, and 15 the back electrode is screwed upon
the base, and the cell wall formed so as to enclose the carbon granules. In each of.
the figures the front electrode is secured upon the diaphragm, and as before
described, is capable of moving with the vibrations of the diaphragm so as to
compress more or less the carbon granules between the two electrodes.
Instead of mounting the cell containing the variable element concentrically with
the diaphragm, I prefer to mount it so that its lower portion covers the centre of
the diaphragm as shewn by Figures 3, 9, 10, 12, 14, 15 and 15ª.
When, as is sometimes preferred, the diaphragm itself is constructed of carbon
or has its inner face coated with carbon, I may dispense with the front electrode
and employ the diaphragm in substitution for it, as illustrated by Figure 14. The
cell may in this case be formed of ebonite C¹ in the form of a ring cemented upon
the back electrode, and very nearly approaching but not actually touching the
diaphragm. In this case also, the back electrode is represented as having a part
nearly approaching to the front electrode or diaphragm as already described with
reference to Figure 9.
It is well known that in transmitters of the type to which these improvements
relate, the granules of carbon or the like, gradually settle and interlock with each
other, thus reducing the efficiency of the instrument. To avoid this result, I may
arrange to blow air periodically through the cell from a small bellows actuated by
the switch but I prefer to shake or disturb the cell each time that the instrument
is used. This mechanical shaking or disturbance of the cell may obviously be
effected in very many different ways. Thus, when a magneto is used with the
instrument for signalling, the cell may be caused to rotate by gearing it with the
magneto, it being for this purpose mounted upon a rotary disc or part on which is
fixed a wheel gearing directly or indirectly with a pinion on the magneto spindle.
Alternatively, the cell may be mounted upon the lever of the switch or hook upon
which the receiver hangs when out of use, so that it is moved or shaken every time
the instrument is used. The method which I have found more convenient in
practice is to mount the cell and diaphragm in a comparatively small casing C
which can slide vertically in suitable guides as illustrated by Figures 1, 2, 3, 4, 5.
The casing C containing the variable element is normally forced upwards by a
spring or springs N of sufficient strength to keep the transmitter and its casing C
in the higher position indicated by the full lines. Figures and 2, but of
sufficient strength to maintain it in that position when any considerable weight
is added. This spring abuts against the stud secured upon the casing. On
the lower part of the casing I secure a hook H upon which the receiver may
be hung, so that when the receiver is placed upon the hook its weight pulls the
transmitter down into the lower position shewn by the dotted lines, and when
the receiver is removed, the spring N forces it up again into the higher position.
The movement of the transmitter may in this case be conveniently employed for
the purpose of opening and closing the several circuits, and is limited by the
stops U and V.
Thus when the transmitter is in the higher position and in use, two contact
springs R R having the usual inoxidisable contacts, press upon two fixed
contacts T T on the transmitter casing. The two spring contacts are connected
with the primary circuit, and when therefore the transmitter is in use, the variable
element is closed in the primary circuit, the fixed contacts being connected
respectively with the front and back electrodes. In the same position of the trans-
mitter, the main line contact spring S is pushed into contact with the contact U₁ of
the speaking circuit. When the receiver is placed upon the hook and the transmitter
is thus pulled down, the local primary circuit through the variable element is opened,
and the main line contact spring falls into pressure with the contact spring R of
the ringing circuit. To effect this result more easily, the speaking and ringing
contacts are arranged vertically above and below the main line contact spring and

page_text: the local circuit contacts are arranged one on each side of the speaking and ringing
contacts. The several contacts and springs are shewn in their respective open and
closed positions by Figures 1, 2, 3, 4, 5, 6, and 8, the dotted lines shewing the
positions when the speaking circuits are open and the full lines shewing them
closed.
On the back of the sliding casing C there are fixed two metallic plates I I¹
separated by an insulating strip J which, or a part of which, projects above the
top of the casing. The plates I I have been formed on the outside of their
opposed edges the dovetailed projections L L' which act as guides. (Figures 5, 6,
and 7.)
On the front of the base A on which the ringing key K is fixed there are secured
the two parallel strips of ebonite or other suitable insulating material M M¹ which
have their opposed inner edges under-cut to correspond with the dovetails L L' on
the plates. The plates are respectively electrically connected with the front and
the back electrodes of the variable element and the fixed contacts T T are secured
or formed upon and in electric contact with them.
For the purpose of concentrating the sound waves produced by the voice, upon
the diaphragm, I may use a coned mouth-piece G with a flange or annular projec-
tion Q, formed or secured thereon as shewn by the section Figure 14. The best
form which I have found for this part is a ring having a U-section, constructed of
indiarubber.
I
When the transmitter is fixed, as shewn by Figures 11, 12, and 13, and I cannot
therefore employ the motion of the transmitter itself to open and close the circuits,
may employ the ordinary pivoted hook H to hang the receiver upon when out of
use. The method of and means for operating the circuits are illustrated by
Figures 18 to 24 inclusive. The back end of the hook lever has two projec-
tions W W one of which W is metallic and the other Winsulated. X' is the
ringing circuit contact spring, X2 the line contact, and X3 X and X the speaking
and local primary contacts. The positions of the circuit contacts in use are shewn
by Figures 18 and 20, and out of use by Figures 19 and 21.
In order to avoid the inconveniences and losses arising from the present method
of constructing the cores of the induction coils used with telephonic transmitters, I'
build up the cores from wires having approximately triangular or truncated
triangular cross sections, or such sections that when collected together they may
form a compact cylindrical body. Contact of the individual wires with each other
may be prevented by any suitable insulating material such as mica or paraffined
paper. If there be more than one ring or layer of the wires then each layer is also
insulated. The method of constructing the core is illustrated by Figures 16 and 17.
A ring or rings of the wires having been introduced into the bore of the bobbin on
which the coil is wound, a conical wedge Y is driven into the centre so as to tighten
and fix them in the eye of the bobbin.
It is possible by this method to make a very cheap and effective bobbin and core,
by simply placing the collected bundle of wires in two flanges Z Z one at each end
of the bundle as shewn by Figure 16. Conical wedges are then driven into each
end as before described. In this case, the eyes of the flanges must be of such a
diameter that the conical wedges will expand the core so as to fill them completely
and fix them. There is in this case no bobbin properly speaking, the barrel being
absent.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. A variable element for an electric telephone consisting of a pair of electrodes
having granulated carbon or similar material between them and having a part of
one of the electrodes in close proximity with the other electrode; constructed
substantially as hereinbefore described and as illustrated by the accompanying
drawings.

page_text: 2. A variable element for an electric telephone contained in a cell mounted
upon a spring or buffer fixed upon the back of the diaphragm and constructed
substantially as hereinbefore described and as illustrated by the accompanying
drawings.
3. A variable element for an electric telephone in which granular carbon or like
material is arranged between two electrodes, in combination with a disc and wheel
or the like upon which it is mounted and through which it is capable of being
rotated by the motion of a magneto used for signalling in the telephone circuit,
substantially as described.
4. A variable element for an electric telephone in which granular carbon or the
like is contained between two electrodes, in combination with a sliding casing on
which the element is mounted, a hook on which the receiver may be hung, and a
spring capable of pulling up the casing when the receiver is removed, substantially
as and for the purpose hereinbefore described and as illustrated by the accom-
panying drawings.
5. In a variable element of a telephonic transmitter, the combination and
arrangement with a fixed back electrode, of a front electrode fixed upon the back
of and moving with the diaphragm, walls surrounding the space in front of the
back electrode and approaching but not touching the front electrode, and
granulated carbon or the like contained within the walls between the electrodes,
substantially as herein before described and as illustrated by the accompanying
drawings.
6. In combination with an electric telephonic transmitter in which granulated
carbon or the like is employed to produce the variable resistance, a small bellows
connected with and actuated by the switch, so that each time the switch is used, a
current of air is passed through the granulated material, substantially as herein-
before described.
7. In combination with an electric-telephonic transmitter in which granulated
carbon or the like is employed to produce the variable resistance, a coned mouth-
piece and an annular flange or projection at the base of the cone, constructed and
arranged substantially as and for the purpose hereinbefore described and as
illustrated by the accompanying drawings.
8. A core for the induction coil of an electric telephone transmitter constructed
of triangular or approximately triangular wires, tightened in suitable flanges or in
the barrel of a suitable bobbin, by conical wedges, substantially as herein before
described and as illustrated by the accompanying drawings.
9. In an electric telephonic transmitter in which granulated carbon or the like is
employed between two electrodes, arranging the variable resistance eleruent in such
a manner that its lower part is opposite to the central part of the diaphragm,
substantially as hereinbefore described and as illustrated by the accompanying
drawings.
Dated this 13th dor of Max A D 1802
WILLIAM E. HEYS,
Agent for the Applicant.