(a) A good working telephone may be made as follows: - Make 2 tin drums 6 in. oximeter and 4 in. deep. They should have a heavy wire formed in same as 1/2 gal. cup. The wire should not be less then No. 9. Take raw hide that has been divested of hair, stretch it over the drum while wet, and bind it on with a small wire; let it remain till perfectly dry. A very thin hide, such as squirrel, cat, coon, is the best. Thick hide will not work well. Now to erect your drum, wire, etc.; having set your posts and put up your insulators, which may be made of wire and suspended from arms which have been nailed to the posts, bore a hole in the wall where the drum is to be placed, run the wire through your drum and through the raw hide in the centre, having a button ready. Pass the wire through the eye of the button and back through the drum and twist tightly, letting the button go, resting it on the hide. Put up the wire, at the different insulators (string loop suspenders) till it reaches the other end of the line; then proceed to do as at first. If the wire has been properly stretched, and all the work has been done as it should have been done, you will have a good and cheap telephone.
No. 18 copper wire for main line should be used. (American Artisan.)
(6) I have been for some time engaged in endeavouring to arrange a telephone switch-board and telephone transmitter, which should be simple, easy of construction, effective in operation, and not an infringement of any patent. I believe that I have fully succeeded in all these objects; a patent for the arrangement could only be valid as for a particular combination of parts, and as the combination of parts is susceptible of so many variations a patent would be practically useless. The following description will enable any amateur to make them: -
Take a piece of mahogany 8 in. by 4 in. by 1 in., plane it up and varnish it. On the top, at a distance of 3/4 in. from the top, fix 7 terminals, 1/2 in. apart. These are numbered in Fig. 131,1,2,3,4,5,6,7, and are for the following connections: 1 2 3 are connected together by the brass plate as shown; 1 is connected to the return line or earth wire; 2 to the zinc pole of the battery; 3 and 4 to the bell wires; 5 to the carbon pole of the first cell; 6 to the carbon pole of the last cell; and 7 to the line wire. P is a strip of brass with the knob K at the lower end; it is secured by 2 screws at the upper end, and is then bent upwards so as to press against the bridge B, which is a strip of brass secured by the screws at each end, each of which screws passes through a piece of brass tube which keeps the plate B about 1/4 in. from the board. The piece P is connected by a wire underneath the board (all the connections are made underneath), with the terminal screw 7. Under the knob K is a screw with a flattened head, which is connected with terminal screw 6; this constitutes the ringing key.
H is a piece of 1/4-in. brass rod with the hook at the bottom, and the round brass disc D about 7/8 in. diameter, soldered about J in. from the upper end; this rod works freely up and down through the two pieces of angle brass A. S is a spiral spring of brass wire which, when the telephone is taken off the hook, causes this rod to rise, and the disc D then presses the thin pieces of hammer-hardened brass G against the upper angle brass A. In order to ensure a good contact, this strip of brass C is slightly canted at the end so as to give two rubbing contacts, one against the disc D and the other against the upper angle brass A. When the telephone is on the hook, the disc D rests on the piece of brass B, which acts as a contact and as a stop. The total play allowed to D is about 3/16 in.; the lower angle brass A is connected with the bridge'B; the piece of brass R is connected with the terminal 4; and the thin piece of brass C with the upper hinge. T and T1 are brass screws to which the flexible wires of the telephone receiver are attached; T is connected with terminal 5, and T1 with the lower hinge.
M is merely a piece of mahogany to which the pieces C and R are attached.
We now require a square frame of 1/4 in. mahogany, 4 in. square in outside measurement, and If in. deep; apertures are cut in the bottom side of this to allow the rod H and the ringing key P to move freely. This case is attached to the hinges marked, and with a face piece of pine about 1/8 in. thick, boxes up the whole of the apparatus, leaving only 2 in. of the board at the top, and the same at the bottom uncovered; a small plate of brass is screwed to this box opposite to the hinges, and one screw into the switchboard prevents the box from being opened.
To the centre of this piece of pine the microphone transmitter shown in Fig. 132 is attached.
This microphone' is thus constructed: - Take a piece of pine about 3/16 in. thick, 7/8 in. wide, and l 3/4 in. long; remove part of one edge so as to leave a projection as shown, and about 1/16 in. deep and 3/16 in. square, by which it is attached to the centre of the pine face of the box; put a sawcut down through it to within about 1/2 in. from the bottom. Take two pieces of l/4 in.carbon rod, E, 11/4 in. long, and cut a recesi in the middle of each half-way through, and a little more than 9/16 in. wide; drill a small hole in the middle of each recess; bend a narrow piece of very thin sheet brass over the top of each arm or leg of tha piece of pine; solder a wire to each piece of brass, and then secure the carbons by screws to the piece of pine as shown in E. These pieces of carbon should be parallel, level, and a little less than 1/6 in. apart; the wire from one carbon is taken to the top hinge, hinge. Some of the carbon rods now sold have a coating of glaze, which is almost a non-conductor. Always remove this with emery-paper. This piece of pine with the carbons attached is now screwed to the centre of the pine rover of the box, and care must be taken that it does not touch anywhere else, and is not touched by anything.
The microphone is completed by making two small conical pieces of carbon N, as shown, with a small hole in the centre of each; a lucifer match or other email piece of light wood is then Hied or sand-papered down until it is as small as a knitting-needle, and will just go into the holes in the-carbon cones. In one carbon cone, put a piece of this wood about 1/2 in. long, and in the other carbon cone a piece about 3/4 in. long, and round the bottom of each of these pieces of wood put a small ring of lead wire; they are then put in position on the carbon rods, and appear as shown in Fig. 132, end view, where E is one of the horizontal pieces of carbon rod, and K the carbon cones; they should oscillate freely. Cut these carbon cones from 9/16 in. rod, I have long been of opinion that the hard carbon microphone works by make-and-break as completely as the Morse tapping key, and that the suggestions as to minute area, etc, were unwarranted by facta. I have also satisfied myself that the Bell telephone or my clear-speaking telephone, and certainly the latter, will reproduce human speech when actuated by an intermittent current, or current of sudden impulses, and that the idea that what Bell describes as an undulatory current is essential to the reproduction of human speech, is altogether untenable.
I wanted to get rid of the spark so often seen in a microphone when a strong battery is used, and which has been the subject of so much learned writing. I believed that this spark was merely due to the well-known "extra current," and I determined to try the plan that has for very many years been in use for getting rid of the spark at the contacts of electric clocks and other apparatus. 1 therefore made a resistance coil of 54-55 ft. of No. 36 B.W.G. German-silver silk-covered wire, which gives a resistance of little more than 100 ohms. I connected the ends of this resistance coil to the two hinges; no spark is perceptible, and the articulation with my clear-speaking telephone as a receiver, is as nearly perfect as anything I have met with in the telephone line. This coil is fastened inside the case above the hinges by a small screw.
1 do not advise the use of induction coils with transmitters, and the above-described switch-board must be altered and made more complicated if they are used; but the arrangement is suited for any good receiver. In connecting up two stations, it will, of course, be remembered that the battery connections at one station must be reversed; that is, the carbon wire attached where I have directed the zinc wire to be attached, and the zinc wire attached where 1 have directed the carbon.
For' battery power, I find that the battery required to ring a fairly good ordinary bell works this arrangement well; thus, if two Leclanche cells ring the ordinary bell nicely, then put one Leclanche cell at each end of the line in circuit with the telephone; if three Leclanche cells are required to ring the bell, then put two cells at one end of the line, and one cell at the .other end in circuit with the telephone.
I have omitted to mention that outside the pine cover to which the microphone transmitter is fixed, I screw by 5 its 4 corners a piece of cork 3 1/2 in. square and about 1/4 in. thick, with a 5/8 in. hole punched out of. the centre. This damps all the sound vibrations, except where they are alone required, that is, in the centre where the microphone is attached, and is a great improvement.
Simplicity and efficiency I have alone had in view, and I believe that anyone, amateur or professional, who may try this arrangement will say that 1 have fully succeeded; whilst as to ccst, this switch-board and transmitter can be made and sold with a fair trade profit for about 15s. (H. B. T. Strangways).