Improvements in Electric Telephonic Transmitters.
Year: 1891

page_text: Date of Application, 16th Sept., 1891
Complete Specification Left, 15th June, 1892-Accepted, 16th July, 1892
PROVISIONAL SPECIFICATION.
Improvements in Electric Telephonic Transmitters.
I, JOHN GRAHAM, of 46 Belmont Street, Haverstock Hill, in the County of
London, do hereby declare the nature of this invention to be as follows:-
My invention relates to that class of telephone known as the "Berthon Trans-
mitter," which consists of granulated carbon held in position between two carbon
plates or diaphragms; the said diaphragms form the electrodes and the granulated
carbon acts as the current variating medium.
The carbon diaphragms are grooved and electroplated with brass or other
material in order to allow of connecting wires being soldered to them, and they are
held in position against three india rubber bands or washers, one on either of the
outer sides of and one between the two diaphragms so that they may be free to
vibrate.
In the process of grooving and brassing the diaphragms, and soldering the con-
necting wires thereto, a number of the diaphragms get broken and destroyed; and,
as the coating of metal is necessarily thin, the connecting wires sometimes become
detached; the rubber washers also pucker or ruffle up when screwing the cap of
the case down upon them, in consequence of which there are more diaphragms get
broken. Under varying conditions of temperature the rubber washers adhere to
the diaphragms or harden and become useless. To obviate these defects. in my
improved transmitter I do away with electroplating, attached connecting wires,
and rubber washers altogether; and, instead of two I employ only one diaphragm.
In a suitably constructed case, say a one similar to an ordinary "watch
receiver" case, I bore two holes through from the inside of the case which pass
out at the back. One of these holes passes through the bottom of the recess
intended to hold one of the electrodes and the granulated carbon, and the other
passes through an abutment or shoulder, intended for the support of the other
electrode or diaphragm.
.
Into the said holes, at the back of the case, I screw or otherwise affix two
terminals; and into the other ends, inside of the case, I place two spiral springs
which fit them just sufficiently to allow of free and parallel action and to project
two or three twists above the edge of the holes.
Against the bottom of the recess I affix one of the electrodes which presses upon.
the enu of one of the spiral springs and is thereby brought into metalic connection
with one of the terminals at the back of the case: this said electrode may be
secured in its place by means of a wooden or other kind of ring of bevelled shaped
rim having its narrow opening at the top which, owing to its particular shape, not
only holds the carbon granuls more compactly, but also so that they are acted upon
more centrely by the upper electrode than they would otherwise be which I have
found an advantage. The other or upper electrode is placed upon the aforesaid
abutment or shoulder of the case and presses upon the end of the other spiral
spring which not only brings it into metalic connection with the other terminal at
the back of the case but which also acts as a buffer in place of an india rubber
washer such as is used in the aforesaid "Berthon Transmitter."
Instead of the electrode and diaphragm being of one piece the electrode
may be of carbon and the diaphragm of wood with a strip of thin hard rolled
metal firmly attached to its inner surface. in a transverse direction to its grains.
or fibres and the carbon electrode revited to the diaphragm against the metal
strip the end of which is; made to press upon the end of the spiral spring as in the
aforementioned instance to form metalic connection between the electrode and the..
terminal. This arrangement gives excellent results.
:...

page_text: The electrodes need not necessarily be of carbon but one or both may be of
metal although I have found carbon to answer the best.
The terminals can be placed both at one side or one on each side of the case if
necessary.
COMPLETE SPECIFICATION.
Improvements in Electric Telephonic Transmitters.
I, JOHN GRAHAM, of 46 Belmont Street, Haverstock Hill, in the County of
London, Electrician, 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 :-
My invention relates to that class of telephone known as the "Berthon Trans-
mitter," which consists chiefly of a quantity of granulated carbon held in position
between two carbon diaphragms, the diaphragms serving as the electrodes and the
granulated carbon as the current variating medium.
I have already particularized in my Provisional Specification the defective parts
in this class of instrument and the means I employ in my improved transmitter to
remedy the same.
And, in order that the construction of my invention may be clearly understood
I will forthwith proceed to describe it in reference to the accompanying drawings
in which like letters refer to like parts.
Figure 1. is a front view, and Figure 2. is a transverse section.
a is an ebonite or other suitable case provided with an aperture or mouth-
piece to direct or focus vocal or other sound waves against the carbon electrode c
which is shown clamped between the body of the case a and its cap and immediately
above and in contact with the carbon particles or granuls d.
In this instance the electrode c, which I will call the front electrode, serves also
as a diaphragm and is clamped at its margin only, consequently free to vibrate in
response to the impact of sound waves impinging against its surface. P is the back
electrode which is preferably also a plate of carbon. It is not however free to
vibrate but is fixed in its place against the bottom of a recess in the case a by
means of a disc or piece of wood or other nonconducting substance w having a hole
through its centre to contain the carbon particles d which bed upon the electrode P.
The hole through w is preferably of a shape narrowing towards the front so as to
hold the particles d more compactly and to insure their being acted upon more
directly by the electrode c. s and are spiral springs inserted in holes passing
through the bottom of the case a to complete the circuit between the terminal t
the electrode P the carbon granuals d the electrode c and the terminal t¹.
I will now describe in what manner my invention as above set forth is, or may
be, operated By an external arrangement the terminals t and t¹ are switched into
circuit with an electric battery, with, or without, an induction coil, as requirements
may necessitate; an electric current is thereby caused to pass from one pole o!
such battery to, say terminal t, thence to the other pole of the said battery by the
spiral springs, the electrode P, the carbon granuals d, the electrode c; the spiral
springs, and the terminal t¹.
1
During the continuance of this current, which is, of course, of a given potential
at any given point, if vocal or other sounds be produced in the vicinity of the
electrode c it will transmit to a receiving instrument the effects of such sounds, in a
rise and fall of potential in the passing current in consequence of its responding
vibrations causing an alternating increase and decrease of superficial contact and
pressure upon the intervening medium d. Hence the transmission of speech; and
musical sounds, and the like..
To render my transmitter more susceptible, or sensitive, to sounds, in place of

page_text: the electrode c being made to serve also as a diaphragm, a thin wooden, ebonite, or
other disc, may be substituted with a piece of carbon for an electrode revited or
otherwise affixed to its centre, with a very thin piece of sheet metal between the
carbon and the disc to make connection with the spiral spring s. It is well
however in the event of wood being adopted to place the sheet metal at right-angles
or crosswise to the fibres or grains of the wood to insure perfect vibrations as other-
wise the wood itself has a tendency to collapse or "buckle" in a line paralel with
its fibres.
Instead of the diaphragm being made of wood or other insulating material it may
be made of metal, such as tinned iron, as shown in Figure 3, in which m is a metal
diaphragm having a piece of carbon c d soldered or revited to its centre by a revit r.
This is a better arrangement than any of the preceding and one that I have found
to give the best results.
A modified form of the preceding described transmitter is shown in section in
Figure 6. It is specially constructed for loud or long distance telephoning. The
constituant parts are the same in this as in the form I have just described but
instead of only one hole to contain the carbon granuals d I employ an insulating
disc D perforated with any convenient number of holes h, such as are shown in
Figure 5. These holes h need not necessarily be round but may be of any other
convenient shape such for instance as are shown in Figure 7. This arrangement
admits of the employment of a stronger battery as it affords the advantage of a
greater number of points of contact without at the same time offering too much
conductive capacity which a single hole would of necessity have to give.
The metal plates M and M' for the terminals t and in Figure 6, and the
terminals t and t' in Figure 2, may, if desired, be affixed to only one or to either
side of the case a with a stem passing through the side of the case to make contact
with the spiral springs & and s¹.
Figure 4. is a side view of the carbon electrode e shown in section in Figure 6.
The case a and the electrodes c and P and the discs w and D need not necessarily
be of a circular shape but they may be of an oval, square, or any other shape if so
desired.
Having now particularly described and ascertained the nature of my inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The combination of connecting springs with parts forming a telephonic
transmitter substantially as and for the purpose set forth in reference to Figures 2
and 6.
2. The combination of a metal diaphragm and carbon electrode with parts
forming a telephonic transmitter substantially as specified in reference to Figures 2
and 3.
3. In a telephonic transmitter a perforated disc for holding particles forming an
intervening medium between electrodes substantially as described and shown in
reference to Figures 5, 6, and 7.
4. In a telephonic transmitter the combination of a carbon electrode acting as a
diaphragm upon an intervening medium of current variating particles held in
position in and by the perforations of an insulating disc, or other shaped plate,
against a fixed carbon electrode substantially as specified and for the purpose set
forth in reference to Figures 4, 5, 6, and 7.
JOHN GRAHAM.

page_text: FIG.4.