An Improvement in Microphone Transmitters.
Year: 1892

page_text: Date of Application, 6th Dec., 1892
Complete Specification Left, 6th Sept., 1893-Accepted, 2nd Dec., 1893
PROVISIONAL SPECIFICATION.
An Improvement in Microphone Transmitters.
GEORGE LEE ANDERS, Electrician, of 10 Jeffrey's Square E.C. and WALTHER
KOTTGEN, Merchant, of 10 Jeffrey's Square E.C. do hereby declare the nature of
this invention to be as follows:-
It is well known, that when electric currents of comparatively high tension are
repeatedly passed through the carbon contacts of a telephone transmitter, there
occurs a deterioration in the points of contact and an increase in the resistance of
the same.
The object of this improvement is to eliminate this defect by placing
the carbon or other points of contact in a vacuum.
Dated this Fifth day of December 1892.
WALTHER KOTTGEN.
GEORGE LEE ANDERS.
COMPLETE SPECIFICATION.
An Improvement in Microphone Transmitters.
GEORGE LEE ANDERS, Electrician, and WALTHER KOTTGEN, Merchant, both
of 10 Jeffrey's Square, E.C. London 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 :-
The object of this invention is to prevent the deterioration or resistance of
conducting matter in loose contact (which takes place between such contacts when
they are used as pencils or grains of carbon) such contacts being commonly used in
microphones.
The injurious effect arising through the use of pencils or grains in loose contact
may be caused by the infinitesimal sparks or arcs which occur between the contacts
under ordinary atmospheric conditions when the current is passed through especially
when the same is of high potential and intermittent, and it may be aided by the
presence of foreign matter such as dust and moisture, most carbons, especially when
used in fine grains or powder being hygroscopic. In order to prevent this
deteriorating effect we place the contacts or conducting material in a vacuum
chamber in such a manner that they are easily affected by movements, vibrations
or sound waves transmitted to them from the outside.
The following description illustrates one form embodying this improvement as
applied to microphones. Referring to the accompanying drawing Fig. 1. A A is
a cylindrical box of ebonite or wood enclosing and clamping the diaphragm B-this
diaphragm is further supported by the metal rings C C. The diaphragm may be
made of metal or any other suitable material. At its centre is attached a glass
cell D which contains a granulated carbon F between two electrodes E and I; the
one attached to the diaphragm consists of a disc of thin platinum E, having its
periphery turned up so as to give it a dish shape. Its diameter is the same as the
internal diameter of the glass tube D and is fused thereto, after which a small
quantity of granulated carbon F is introduced, then the bullet shaped plunger
having a requisite weight and faced with a block of hard carbon
presses the
carbon granules gently against the dished electrode E. The electrode E can be
attached to the centre of the diaphragm B by a screwed stud soldered to the centre
of the platinum. This stud passes through a collar to which is attached one of the
conducting wires M and through the diaphragm to which the whole is securely
fastened by the nut N. The bullet shaped plunger, consisting of the parts I H H'G,

page_text: fits the inside of the glass tube in such a manner as to prevent the granules F
escaping from between the electrodes E and I. After the carbon and plunger
have been introduced into the tube, the latter is heated and drawn out at the upper
end to a smaller diameter of sufficient length, after which it is attached to the
exhausting apparatus, and when sufficiently exhausted is sealed off, leaving the
platinum wire J projecting. To the projecting platinum wire J is attached a
conductor O. The cell D is then attached to the diaphragm in the manner already
described and it is further supported by a lining of felt P between itself and the
case A. It will be seen that when so connected any vibration of the diaphragm
will be communicated to the thin walls of the dish shaped platinum electrode E and
consequently to the carbon granules F, and as the latter are cut off from atmospheric
effects, the desired object is attained. The construction of the plunger is as
follows: A cylindrical piece of brass G, slightly less than the internal diameter
of the glass tube D, having a hole through its centre, is placed between two asbestos
washers H & H¹. At the end next to the carbon granules F is a semispherical
carbon block I, at the opposite end is a washer of metal K. Through the whole
of these parts passes a small bolt L which clamps all of them firmly together.
This bolt L is connected to the coiled platinum wire J. It will be seen that the
asbestos washers H & H serve the purpose of not only retaining the carbon
granules F between the electrodes E & I, but also that the plunger may move
freely when pressed forward by the platinum spiral J, and further they will not be
damaged by the heat to which they are exposed in the process of fusing the glass.
This microphonic cell D is capable of being used with induction coil or for what
is usually termed "direct" working.
It must be understood that we do not confine ourselves to the introduction of
carbon granules into the exhausted cell, as carbon pencils and other shapes or
forms of conducting matter may be used instead. Neither do we confine ourselves
to the described method of attaching the exhausted cell to the diaphragm, if such
be used, which in some cases may not be necessary.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is:
1. The introduction of conducting matter capable of microphonic action into an
exhausted chamber or vacuum for the purpose set forth, substantially as described.
2. An exhausted chamber or vacuum having a thin conducting wall capable of
mechanically transmitting vibrations to the microphonic material contained therein
substantially as described.
Dated this Sixth day of September 1893.
GEORGE LEE ANDERS.
WALTHER KOTTGEN.