One of these obscure phones was sold on eBay in 2006. Apart from the occasional mention in reference books, it is almost unknown. What little is known is presented here. The Pantelephone was another attempt to get around the Bell patents, and to make a transmitter that was a little more sensitive than Bell's Blake-Berliner model. Unfortunately the patents held by the Bell company effectively blocked the use of most alternative ways of building a telephone transmitter.
Leon de Locht-Labye, a Professor at Liege University in Belgium, published details of one such transmitter in 1880 in his work entitled "La Téléphonie - Sa Théorie, Ses Applications - Le Pantéléphone" (very roughly, 'The Telephone - Its Theory and Applications - The Pantelephone'). The biggest drawback of Bell's transmitters is that they were not very sensitive, giving a very low transmission level and short range. With a single-contact transmitter, this meant that any increase in volume or distance required a bigger diaphragm. This was Locht-Labye's approach.
He described a transmitter that used a suspended sheet of cork, mica or metal for a diaphragm, about 15cm on each side, and an adjustable weighted or sprung arm with a platinum or silver bead cemented to it pressing on the diaphragm. A corresponding bead or carbon strip was riveted to the diaphragm. An induction coil completed the circuit and stopped the "make and break" effect when the diaphragm was moved too violently by people shouting into it. An Ader-type receiver completed the phone. Although the telephone probably ran foul of Edison's carbon contact transmitter patents, it went into limited production for a brief period.
From the few comments available it was a fairly good, sensitive transmitter. It could apparently carry a call for several miles on a single-wire circuit, and a conversation could be picked up twenty metres away from the transmitter. Its sensitivity was due to the large diaphragm area, but this was also a drawback. As can be seen from the photos, the works were covered by a simple fabric screen. This would not have provided much protection to the internals. The transmitter was also sensitive to bumps and knocks, and it would have been impractical to build it into a desk phone.
The lower diagram shows the bent metal bracket and adjusting screw that held the contact arm onto the diaphragm.
Diagram from "Electricity In The Service Of Man" 1886
The excellent photos provided by the eBay seller show the internal construction clearly. The arm appears to be brass, with a German Silver disc soldered to it. The adjuster screw is at the base of the arm, just above the pivot. The diaphragm is the large solid-looking slab of cork suspended from the top of the case. The switchhook has an improvised but solid look to it, as does the bell ringer magnet assembly. The whole assembly was usually mounted on a heavy timber or metal backboard so that only the diaphragm would move. A cloth cover concealed the works and let the sound waves through to the diaphragm. The fabric is impressed with the Locht Labye name, and Brevete, which equates to "patented".
Even the peripheral parts, the bell, earpiece and wall mount brackets, show careful design for strength and durability. This probably explains why the phone is still in good condition after more than a century.
Interior view showing the cork diaphragm and the arm holding the second contact pressing against it. Because of its unusual internal design, it may not readily be recognised as a telephone by collectors who may have one.
Lower terminal arrangement
The example on eBay is from South America, where many were sold into Argentina in the 1880s. The Societe du Pantelephone opened in 1881 in Buenos Aires and appeared to have some success, although the Government initially restricted it to twenty phones. Other companies opened about the same time, and after a few years they all amalgamated.
These images are from an early catalog, and show external fittings that are not present on the eBay example. Internally the fittings are much the same, but note the external lightning arrestor at the bottom and the long-pole Bell-style receivers.The dual receivers were a convenient way of reducing background noise while on a call, and boosting the received signal al little.
Some Pantelephones were apparently also used in a number of European cities.
Does anyone have any more information?
I am extremely grateful to the seller for generously supplying the high resolution photos of this extremely rare telephone.