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MAGNETIC RECEIVER of the 1880's


Siemens & Halske, Berlin


by Ken Bushell


A Brief History.

Telephones of the Bell type were introduced into Europe in 1877 and these were used for early experimental connections. Basically, Bell's set was simply an earphone which was used as a receiver and as a transmitter. The currents produced however, were very weak and the set was therefore less suitable as a transmitter. Some improvements were made in the years after 1876 by Thomas A. Edison and F. Blake, both from America and by Werner von Siemens from Germany.

In 1878, the Swedish authorities most concerned, above all the Telegrafverket, showed little interest in the telephone. In Germany on the other hand, they reacted more promptly and had copies of the Bell set ordered from Siemens and Halske in Berlin, one of the leading electrical engineering companies. To copy the Bell instrument was possible because Bell had not taken out any patents in Scandinavia or Germany.

Some of these sets found their way to Sweden, to the Ericsson workshops for repair and at the end of 1878, LME began to manufacture telephones using the Siemens and Halske magnetic telephones as prototypes. These LME sets were made from 1878 to 1880 but there was not a great demand for them (approximately 400 being made). These telephones were very similar to the Siemens and Halske instruments described below.

The telephones that are the subject of this article were made in Germany by the Siemens and Halske Company in Berlin in the 1880's. They were used chiefly in Germany and were exported to other countries including Australia. Two instruments in the collection of the writer were used in Tasmania. Few of these instruments survive today.

The following description is from a book titled "THE TELEPHONE" by William Henry Preece F.R.S. and Julius Maier Ph.D., published by Whittaker & Co., London in 1889. Further notes and pictures are from Ron Knappen's "Old Telephone Scrapbook", "L.M. Ericsson 100 Years" and from other sources.

Description.

On the horse-shoe magnet mm two steel polar pieces ss, are fastened by means of screws. The polar pieces carry the small oblong soft iron cores uu, which are wound with fine insulated copper wire.

The horse-shoe magnet is joined to the plate ee by means of a screw q, which passes through the iron plate ee, through a wooden block i fixed to the plate and through a brass plug in the centre of the wooden block. When, therefore the screw is tightened, the magnet is lowered, whilst it is raised by the opposite action of the screw. Two small boards hh press on either side against the two extremities of the magnet and serve fro the reception of the wires rr, which are connected to the convolutions of the two coils uu. The wires rr end in two screws fastened to either side of the block i, and the line wires start from these screws.

An iron stirrup gg for the suspension of the instrument is fastened to the plate ee. (these are only on sets used as wall units).

The whole mechanism is placed in a cylindrical tube of sheet iron cc (Fig. 2) in such a manner that ee forms the foundation plate of the apparatus. The tube carries a top piece bb, and is above b closed in the interior by means of a round piece of sheet iron. The apparatus terminates in a conical mouthpiece aa of polished wood, in the centre of which is a round opening lined with brass.

The distance of the magnet from the membrane is regulated by means of the screw q, an arrangement which has been adopted in a number of other telephones.

Siemens' apparatus differs from Bell's latest pattern only in the form of the magnet which it employs. The straight unipolar magnet has been replaced by one of the shape of a horse-shoe, and also the iron membrane is larger and stronger than that of the Bell instrument. (Bell's original telephone contained a horse-shoe magnet).

The above description is as published in 1889. The writer's instruments are made of brass and the wooden earpiece appears to be polished walnut).

Calling.

The call is effected by a small whistle or reed, which is blown before the diaphragm of the transmitter, and produces a shrill tone in the receiver more than sufficient for the purpose. This whistle is attached to the wooden earpiece by a small piece of cord as shown (Fig. 3).

The whistle (Fig. 4) consists of a conical tube of hardened india-rubber, in the interior of which an angular metallic piece ww is fastened by means of screws. A vibrating reed b is fixed at one end to the piece ww, and free to vibrate at the upper end. The lower part of the angle ww is perforated, and in the perforation plays a rod h provided with a small clapper.

On blowing into the whistle, which is fastened to the top of the apparatus as in (Fig. 3) sound like that of a penny-trumpet is produced; the clapper which touches the iron membrane by its up and down strokes strengthens the vibrations of the latter, so that a shrill loud tone in the receiver is the result. Care that the whistle was removed from the earpiece was necessary to avoid damage to the ear.


A second type of calling device is shown in (Fig. 5), this has a small handle which, when turned, vibrated the diaphragm to cause a similar sound to the above.

This is a very efficient form of telephone receiver, and is quite powerful enough to be used as a transmitter. These instruments were used for point to point communication and were used as a receiver and transmitter (Fig. 6) which meant changing from listning to talking.

It is a rather expensive instrument owing to the numerous parts and materials employed. One of the main objections to doubling these telephones was the costliness of good horse-shoe magnets, which are not easy to make.

Later telephones incorporated two units as shown in (Fig. 7) and included electric bells. This illustration is dated 1885.

Original drawings re-drawn by Ken Bushell.

Thanks to Terry Aucher for much of the information.

Original article appeared in March 1994 edition of the ATCS Newsletter.









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