Electro-Telephonic Appar
Year: 1886

page_text: Date of Application, 27th May, 1886.
Complete Left, 28th Feb., 1887.
Complete Accepted, 29th Mar., 1887.
RESERV
ALAN ARCHIBALD CAMPBELL-SWINTON, Engineer, of 43 Grove Street Newcastle on
Tyne, do hereby declare the nature of this invention to be as follows :-
My Invention relates to improvements in Electro-Telephonic Apparatus such as is
described in "The English Mechanic" for Friday, August 11th 1876, and has for its
object increased efficiency and convenience in practical working.
According to my invention I in some cases construct the drumheads by joining
together, flat-wise, two or more membranes of bank-post paper or other suitable
material, preferably saturated with stearine, paraffin, or other similar substance, by
means of shellac in a fused condition, the armature of clock spring or thin soft iron
being preferably inserted between the membranes, and sometimes I find it advan-
tageous to protect the exterior surface or surfaces of this drumhead, or one constructed
of a single membrane, with a coating of shellac applied as above in a state of fusion.
In some cases I mount the drumhead on a carrier ring of metal or other suitable
material, which ring may be made of the same thickness as the armature and inserted
between the membranes before their union by means of the melted shellac, and I
sometimes make the carrier ring and armature out of one piece of sheet soft iron, the
armature being supported by one or more tongues projecting inwards from the ring,
the whole being preferably contained between the membranes forming the drumhead.
I also in some cases find it simple and convenient to employ the drumhead alone
without any carrier ring, and simply clip its circumferencial edge between the mouth-
piece or cover and the other portion of the case of the instrument, a loose ring of
paper, cork or other yielding material being advantageously inserted in order to ensure
equal distribution of pressure.
Drumheads manufactured as above are remarkably sensitive, and have the further
advantages of being unaffected by changes of temperature and by alterations in the
hydroscopic condition of the atmosphere.
-
Behind the drumhead, and fixed in a suitable case which may conveniently form
the handle of the instrument, I place the Electro-magnet the core of which is of soft-
iron. I find it advantageous to employ a coil the axial length of which is about equal
to its diameter, and to make the core of small sectional area within the coil, but with a

page_text: considerable mass of metal extended beyond the coil on the side thereof removed from
the drumhead.
As I find it very important for the effective working of the instruments that the
cores should possess a high degree of primary magnetism, and as where the resistance
of the line is considerable this entails very large battery power should the coils, line,
and batteries be all arranged in simple series as is the case in the hereinbefore alluded
to arrangement described in the "English Mechanic " I find it most advantageous
where the line resistance is high, to employ the following arrangement according to
which the said line resistance does not affect the degree of primary magnetism
produced by the batteries in the cores.
Where two or more similar instruments are employed at one station, one for trans-
mitting, and others for receiving, I connect them one or more in each of two parallel
circuits to main line and earth, the battery being inserted in one of these circuits, and
I so arrange the batteries at the two ends of the main line that they balance one
another as regards the said main line and send no current through it, but only through
the instruments at their own individual stations.
When a microphone transmitter is employed, without an induction coil, I employ a
similar arrangement, the microphone taking the place of the transmitting telephone,
and in this case I prefer to insert the batteries in the particular circuits in which the
microphones are placed, this arrangement leading to alternating currents passing
through the line as the resistance of the transmitting microphone is increased or
decreased in unison with the operating sonorous vibrations.
When induction coils are used with the microphones and transmitting batteries
arranged in their primary circuits, I insert the secondary coils in the main line,
and on the earth side of the same, I split the line as above into two branches
placing one receiving telephone, or one of the two coils of the two magnets, one
on each side of the drumlicad. I employ in one telephone, when only one receiver is
used, in each branch, the magnetising battery being inserted in one of the branches
and preferably balanced as regards the main line by the battery at the other station as
hereinbefore described.
When this arrangement is employed in practice with the usual automatic switch,
and the magnetising batteries serve also to ring the call bells, I find it advantageous
to so arrange the switch that the secondary wire of the induction coil is short circuited
when the line is to carth through the call bell, the normal state of matters when the
instruments are not in actual operation; this being for the purpose of obviating the
resistance of the said secondary wire which would otherwise entail increased battery
power to ring the bell.
In some cases I connect the receivers and the secondary of the induction coil all in
separate parallel circuits between the main line and earth, the magnetising, battery
being insorted in one of the receiver branches according to the manner herein before
described.
When a third Station is included in the Circuit, and for this or for any other
reason, it is necessary that absolutely no battery current should pass through the
main line and also when this is requisite with only two stations, I find it convenient
to insert a Condenser of suitable dimensions in the main line circuit, this precluding
the possibility of any battery current due to inequalities in the batteries from passing
through the main line from one station to another.
The use of the Condenser also obviates the necessity for balancing the batteries in
the case of only two stations.

page_text: I ALAN A. CAMPBELL SWINTON of 43 Grove Street Newcastle - on - Tyne
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 :—
My Invention relates to improvements in electro telephonic apparatus such as is
described in The English Mechanie" Newspaper for Friday August 11th 1876 and
has for its object to obtain increased efficiency thereof and convenience in practical
working.
According to my Invention I employ for covering the armature, carrying membrane
or membranes constituting the drumheads of the transmitting or receiving instru-
ments or both or for connecting several such membranes together or for both
covering and connecting such membranes and armatures, a resin, such as shellac
fusible by heat. For example I may construct the drumheads by joining together
flatwise two or more membranes of bank post or other strong but thin paper or other
suitable material preferably previously saturated with stearine, parafine bees wax, or
other similar substance, or two or more membranes of ordinary tacing paper or cloth
by means of resin, such as shellac, in a fused condition, the armature of clock-spring
or thin soft iron being preferably inserted between the membranes, and sometimes
find it advantageous to protect the exterior surface or surfaces of this drumhead, or
one constructed of a single membrane, with a coating of the shellac or resin applied
as above in a fused condition.
One way of making drumheads according to my Invention is to take two
membranes and insert between them the armature and the shellac or resin, the latter
being in any convenient form and then to press the whole together between heated
metal plates whereby the shellac or resin is fused and the whole firmly connected.
Another manner is to coat the membranes in the first instance with the shellac or
resin and then to press them together, with the armature placed between them, between
heated plates as hereinbefore described.
Or I may stretch or mount the drumhead on a carrier ring of metal or other
suitable material, which ring may be made of the same thickness as the armature and
be inserted between the membranes before their union by the means described. The
carrier ring and armature may be made out of one piece of thin sheet soft iron, the
armature being supported by a tongue or tongues projecting inwards from the ring,
the whole being preferably contained between the membranes forming the drumhead.
I may clip the drumhead between two rings of brass or other suitable material

page_text: rivited or suitably fastened together and these rings may be conveniently made so as
to stretch the drumhead when they are fastened together, so as to maintain the drum-
head in a state of tension. Or I may employ the drumhead alone without any carrier
ring, and simply clip it at the circumference between the mouthpiece or cover and the
other portion of the case of the instrument, and a ring of paper cork or other yielding
material, may with advantage be inserted between the drumhead and the case or cover
in order to insure an equal distribution of pressure.
Drumheads manufactured and supported, stretched or mounted as above described
are very sensitive and have the further advantages of being unaffected by changes of
temperature or by alterations in the hygroscopic condition of the atmosphere.
Behind tho drumhead, and fixed in a suitable case which may conveniently form
the handle of the instrument, I place the electro magnet the core of which is of
soft iron.
Where induction currents are employed I find it advantageous to employ a coil the
axial length of which is about equal to its diameter, and to make the core of small
sectional area within the coil but with a considerable mass of metal extended beyond
the coil on the side thereof removed from the drumhead.
However with the transmitting microphones in direct circuit with the receivers
without the employment of an induction coil this mass of metal may be advantageously
dispensed with.
As I find it very important for the effective working of the instrument that the
cores should possess a high degree of primary or constant magnetism, and as where
the resistanco of the line is considerable this entails very large battery power should
the coils line and batteries be all arranged in simple series as in the case with the
arrangement described in the "English Mechanic" as aforesaid I find it very
advantageous where the line resistance is high to employ one of the following arrange-
ments of connections according to which the said line resistance does not affect the
degree of primary magnetism produced by the batteries in the cores.
Where two or more similar instruments are employed at one station, one for
transmitting and others for receiving, I connect them one or more in each of two
parallel circuits to main line and earth as shewn in Figure 1. where E is earth.
TT are two telephone instruments and BB the batteries inserted as shewn one at
each end of the line in one of the parallel circuits, and I may so arrange the
batteries at the two ends of the line that they balance one another as regards the said
line and send no constant current through it, but only through the instruments at
their own individual stations. When a microphone transmitter is employed without
an induction coil, I employ a similar arrangement, the microphone taking the place
of one of the telephones, and in this case I prefer to insert the batteries in the
particular circuits in which the microphones are placed as shewn in Figure 2,
where M M are the microphones this leading to alternating currents passing through
the line as the resistance of the transmitting microphone is increased or decreased in
unison with the operating sonorous vibrations. When induction coils are used with
the microphones and transmitting batteries arranged in their primary circuits I
sometimes insert the secondary coils in the main line, and on the earth side of the
same I split the line as hereinbefore described into two branches, placing one receiving
telephone (or one of the two coils of the two magnets one on each side of the drum-
head employ in one telephone, when only one receiver is used) in each branch, the
magnetising battery being inserted in one of the branches and preferably balanced as
regards the main line by the battery at the other station as hereinbefore described, the
whole being substantially as shewn in Figure 3 where II are the induction coils, M. B,
the magnetizing batteries and T B the transmitter batteries the other letters being as
before.
In some cases I find it convenient to employ but a single set of batteries at one
station and in this case I take the current requisite to operate the transmitter circuit
off one or more of the cells of the magnetising battery by means of shunt wires
connected thereto.

page_text: When the arrangement is employed in practice with the usual automatic switch
and the magnetising batteries serve also to ring the call bells, I find it advantageous
to so arrange the said switch that the secondary wire of the induction coil is short
circuited when the line is to earth through the call bell, the normal state of matters
when the instruments are not actually transmitting speech; this being for the purpose
of obviating the resistance of the said secondary wire which would otherwise entail
very great battery power to ring the bell.
In order to effect this the arrangement at one station may be as shown in Figure 4
where S is the automatic switch which may be of any ordinary construction and
where K is the key for calling attention, the other parts being lettered as in the .
preceding figures.
In some cases I connect the receivers and the secondary wire of the induction coil
all in separate parallel circuits between the main line and earth, the magnetising
battery being inserted in one of the receiver branches according to the manner herein-
before described, the arrangement being as shewn in Figure 5, or the magnetising
battery may be inserted in that part of the main line that is included between the two
receiver branches as shewn in Figure 6. When a third station is included in the
circuit, and for this or for any other reason it is desirable that absolutely no battery
current, should pass through the main line, and also, when this is requisite, with only
two stations, I sometimes find it convenient to insert in the main line a condenser.of
ordinary construction and suitable dimensions, this precluding the possibility of any
battery current due to want of balance in the batteries from passing through the main
line from one station to another.
The use of the condenser also obviates the necessity for balancing the batteries in
the case of only two stations.
While preventing the passage of direct battery currents the condenser does not
materially impede the action of the induction currents which generated in the induction
coil at one station actuate the receiving apparatus at another.
Having now particularly described and ascertained the nature of my Invention
and in what manner the same is to be performed I declare that what I claim is :-
First In electro telephonic apparatus in, or for, the transmitting or receiving
instruments a drum-head made by joining two or more membranes of the nature
herein before described together with an armature by means of a resin such as shellac
liquified by fusion or heat substantially as hereinbefore described.
Second-In electro telephonic apparatus in, or for, the transmitting or receiving
instruments a drum-head made of a membrane or of membranes of the nature herein-
before described with an armature and covered, or coated by a resin or shellac applied
thereto by fusion or heat substantially as hereinbefore described.
Third-The manufacture of drumheads for telephonic transmitters or receivers by
connecting or coating (or both) a membrane or membranes of the nature herein before
described and an armature by means of a resin such as shellac fused or liquified by
pressing between heated plates substantially as herein before described.
Fourth For telephonic transmitters or receivers a drum-head and armature of
the kind hereinbefore described and claimed by either of the preceding claiming
clauses mounted on a ring with an armature connected to the ring by a tongue or by
tongues (or independent of the ring) and secured in the instrument all substantially
as hereinbefore described.
Fifth In telephonic apparatus the combination of two or more parallel circuits at
each station of the line there being a battery in one of the parallel circuits at each
station of the line and telephone receivers transmitters or parts of these or the
secondary of the induction coil in each of the parallel circuits at each station of the
line substantially as described with reference to the several examples given in
the accompanying drawings.

page_text: Sixth In telephonic apparatus as claimed by the last preceding claiming clause
the balancing of the batteries at the station of the line substantially as and for the
purpose hereinbefore described.
Seventh In telephonic apparatus as claimed by either of the last two preceding
claiming clauses wherein induction currents are used the employment of a condenser
in the main line substantially as and for the purpose hereinbefore described.
Eighth The several telephonic arrangements hereinbefore described and illustrated
in the several figures of the accompanying drawings.
Dotad the 94th day of Fahu 1007
ALAN A. CAMPBELL SWINTON.