The BERTHON-ADER Wall Telephone
Reprinted from the May 1988 issue of ATCS newsletter
"Telephones are now very often used on Government lines both in these States and in other countries. They afford a ready means of communication and can be used by persons unskilled in telegraphy. It is very desirable that officers who use them should have an intelligent knowledge of their principles and mode of working, as it is an instrument the use of which is certain to spread widely."
The above was the comment by H. W. Jenvey of the Victorian Postal Department in 1904. He then proceeded to describe the Berthon-Ader local battery magneto telephone which, at that time, was in use by several Australian state administrative and railway departments.
The phone is of French origin and the first model is credited with having been produced in 1885. This model is fairly rare and not many examples are held in Australia.
The model most commonly found in Australia dates from about 1890 and a few exist in private and public collections throughout the country. One of its distinguishing features is the awkwardly shaped handset shown in figure 1. The transmitter is of a large diameter and, in use, must be held at an angle of 50 degrees.
The telephone was manufactured by Societe Industrielle des Telephones, Paris (roughly translates into Telephone Manufacturing Company - Paris). The French inscription appears on two small engraved plates on the front of the box as well as on both the handset receiver and the auxiliary receiver.
These latter two are additionally inscribed ‘Systeme ADER’ which means ‘ADER System’ and refers to a modification introduced by M. Ader to improve the sensitivity of the receiver. The construction of the magnet and coil part of the receiver follows fairly conventional lines but above the diaphragm is placed a small circular ring of soft iron (figures 2 and 3). This arrangement is termed ‘sur exciteur’ or over-exciter, for the purposes of concentrating the magnetic field. The receiver is very efficient but the system was not carried on with later receivers.
One of the two plates on the front of the telephone is inscribed ‘Systeme BERTHON’ which obviously translates to ‘BERTHON System’. This refers to the microphone, the construction of which is shown in figure 4. It consists of an ebonite box B into which is assembled a
carbon backing plate with a carbon cup attached and a carbon diaphragm on the side on which speech impinges (top side). The diaphragm is protected by a pierced metal plate which is not shown in the drawing. Carbon granules are placed in the carbon cup to provide the necessary variable resistance path. The microphone is switched into circuit when the handset is lifted from the hook.
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The combination of the two names of Berthon and Ader who contributed to the design gives the appellation by which this phone is generally known - BERTHON-ADER.
The box which covers the internal parts of the phone is removable from the front. It is located by two studs into matching holes in the backboard; then is it secured in place by two hook catches, one on each side, and finally locked into place by a key which enters through a hole in the middle of the oval nameplate.
The next point to look at is the circuit diagram (figure 5) which has all the usual components but includes long spring contacts which simply press against the switchhook lever. These must have been a constant source of problems. In common with most phones of the period, a lightning arrester was included and provision was made for inserting a shorting plug when storms were about. Too bad if you wanted to use the phone and forgot that the shorting plug was still inserted.
The magneto (figure 6) has 3 well spaced magnets and is held against the backboard by two screws. It has helical cut gears with quite a large diameter gearwheel, so large in fact that a groove had to be cut out of the backboard to accommodate it. The magneto electrical cut-out consists of a disc on the drive shaft with a long spring contact. Magneto resistance is 500 ohms and generates an EMF of 50 to 60 volts.
Two engraved plates are attached to the cover, one rectangular and the other oval in shape. Both carry the manufacturer’s name and a number. The numbers are not the same, that on the rectangular plate being the serial number of the phone which is also stamped on the bottom right hand side of the backboard.
The oval plate has the keyhole in its centre to enable the cover to be locked in place as previously mentioned. The significance of the number stamped on this plate is not known.
As recovered from Victorian Railways, the plates are usually turned over to present their blank sides. Presumably this was done when phones were refurbished which would also account for serial numbers on plates and backboards not matching in many instances. The engraved side should be to the front.
Bells - Mounted on backboard above box
Generator handle - curved
Nameplate - Rectangular above oval plate
Bells - Mounted on front cover of box
Generator handle - Straight
Nameplate - Oval plate above rectangular plate
Ref: Practical Telegraphy by H. W. Jenvey, M.I.E.E. fourth edition, 1904.