Ericsson AC100 Series "Skeletal" Desk Phone

This telephone has an important place in telephone history, as it was the world's first production handset telephone and thus set a trend that the rest of the world followed. L M Ericsson sold his parts to other companies so the phone is found in many varieties. Some are shown here.

First, though, it will be necessary to clear up one point - that of identification. Ericsson never called the phone a "skeletal". That name (and many others) was applied by some collectors. In the United States, collectors call the phone the "Eiffel Tower". That name is used by most European and Australian collectors to refer to a telephone from Bell Telephone Manufacturing in Antwerp, and later from Western Electric's British and possibly Spanish factories. I know we are not going to change decades of conflicting naming, but just so we know what phone we are discussing:








The Ericsson phone on the left will be called a Skeletal or Skeleton, and the BTMC/Western Electric phone on the right an Eiffel Tower.



Ericsson's earliest desk phones did not look like this. There was a brief period of evolution before the phone took on its final shape, made necessary by the transmitters of the time. The best transmitters were filled with granules of carbon, usually carefully-graded anthracite coal (hence the name "coal-grain transmitter" seen on many of them). In the wall phones of the time, they were attached to the front of the case. This allowed the coal grains to settle to the bottom of the transmitter enclosure ("packing") which reduced their efficiency.


Lars Ericsson's solution was to mount his Spiral coal grain transmitter horizontally, and this let him produce a compact desk phone in 1881, known to collectors as the "Lily".


Photo courtesy Ove Svensson


This phone, as well as being one of the world's first desk phones, could also be regarded as the forerunner of the candlestick style. It is extremely rare.



The Model AC100 (early number 370) was introduced in 1884 and continued in production until at least 1888 with the Spiral transmitter. This was then upgraded to a new carbon grain transmitter that worked better when vertically mounted. The phone continued in production until 1890, although it was soon overtaken by the later handset model. In spite of this it was still shown in catalogs through the early 1900s. Any orders were apparently filled from old stock.

The phone was designed by Lars Ericsson himself. At this time his firm was still small enough to allow him to take a direct hand in design and construction. The magnets for the generator were formed into the legs for the phone. The coil was built into the turned wooden turret base, and the bells suspended underneath the phone. The ebonite "deck" carried the lightning arrestor and terminals. The turret and legs were finished in black "japan" enamel , and other metal parts were nickel plated. In later models some pillars were finished in polished and lacquered brass, the golden color providing an attractive highlight to the phone. It may also have been a useful method to reduce the cost and speed up the production a little when demand for the phone increased. The legs were attractively decorated with gold and red transfers.

The phone is notable for its "swing-arm" or "turret" design, allowing the transmitter to be swung around so a user on the other side of the desk could also use the phone. A two-receiver model was also produced for the same purpose, with the second receiver mounted on the other side of the pillar on a second switchhook arm.

Although the phone seems to have been initially popular, the later handset phone proved even more popular and many AC100s were converted to handset operation. They are now extremely rare in the original style. In the late 1990s a small run of a conversion kit was available in Australia to convert a handset phone back to the Turret style.


The No. 375 (later AC110) was introduced in 1890 in Sweden and 1892 elsewhere, and continued in production for around forty years with minor changes, mostly to the transmitter. It has been known to have been built or assembled in Russia, Britain, France, Sweden, U.S.A., Mexico, Brazil, Portugal, Denmark and Germany. It was solid, well built and beautifully finished and it is not surprising that it has become a favorite with collectors. It appears to have been an overnight success and many telephone builders sourced parts from Ericsson to build their own versions. We will look at some of these later.

A British Ericsson catalogue describes it modestly : “This exclusive instrument is a masterpiece of unique design and is undoubtedly the handsomest set in the industry”.

The example shown is fitted with an early modification, a brass fitting on the pillar to hold a card with the telephone number on it. Other options were gradually added to the range. The standard cord was green but other colored cords could be provided on request. The metal could be gold-plated, and an ivory finish was available - all at an added price.

A two-crank model No 385 (later renumbered AC200) was added to the range to allow working from both sides of a desk. This had the handset mounted across the axis of the generator, and it is uncommon.

The earliest versions had a wooden handset grip with coarse flutes on the side, but this was changed to an ebonite grip with finer flutes. The receiver was also changed at this time. The older version had an ebonite earpiece held onto the handset with a knurled metal ring. In later versions this was replaced with a one-piece ebonite moulding that screwed directly onto the receiver, as shown on this example.

A "sanitary" handset was also available, with a metal cap over the mouthpiece that made the handset easier to sterilize. At this time the world was becoming conscious of Tuberculosis, a very nasty and often fatal respiratory disease that could spread through saliva droplets carried on a person's breath. Sanitary handsets or sterilizable mouthpieces were available from many of the world's telephone companies.

Around 1900 a minor modification was made to the wiring to the bell motor. In the earlier models a wire was run from a small brass plate mounted on the deck just above the motor. Post 1900 models had this replaced with two metal straps running from screws mounted directly in the deck to the bell motor. This may help date phones on which the serial number has been damaged or the wrong handset fitted.


Left: The bell motor connection on later phones. The brass plate on earlier phones was mounted just above these.





1908 to 1914, the outbreak of World War One, saw the bulk of production.


Only one change remained. From around 1920 an improved transmitter was introduced with a slightly deeper dome. The handset grip was now produced in bakelite. This example also shows a later simplified cradle that was being introduced on Ericssons' phones, in the interests of faster production and lower cost. Some companies were still buying the Skeletal, and it still appeared in Ericsson catalogs coexisting with tin box style telephones and candlestick phones, but by now many of the phones were assembled from remaining parts in stock rather than from production runs. Finally economics won out and the design was replaced by the "tin box" style phones, where cheaper finished parts were enclosed in a rectangular steel box. These in turn lost out to the new bakelite telephones.



The phone lived on in service for many more decades. During the Second World War the Swiss telephone administration still had over 3000 in service. The last one in Australia is reputed to have come out of service from a dentist's surgery in about 1978. There is an unconfirmed report of one still in use in the 1980s in Tasmania. In 1984 a limited edition replica was issued by Ericssons to mark the 100th anniversary of the phone, possibly at the suggestion of the Swiss administration. The Skeletal earned its place in telephone history.


The critical component was the transmitter, so a closer look is appropriate. The principle of carbon granule transmitters had been thoroughly researched by Edison, whose patent was now owned by the Bell company. Bell omitted to patent his transmitters in Sweden so Ericsson was free to develop on the idea without facing litigation. The main problem of carbon granule transmitters was their tendency for the granules to pack down at the bottom of the transmitter, reducing the efficiency. In its most basic form a granule transmitter consisted of a backplate, a diaphragm at the front, and carbon granules in between. Ericsson refined his original Spiral transmitter design extensively and produced a transmitter that was practically free from packing.

The following description is from Poole's "Practical Telephone Handbook" , 1912.







"The instrument is made up in an aluminium case , A and B, made in two parts. The back part of the case B has a recess, in which fits a 7/8 inch round carbon block, C, 1/4 inch thick. The front face of this block has seven holes drilled in it - one in the centre, in which fits the head of the long, clamping and connecting screws, and six other holes, as shown in Fig. 73 (which gives a separate view of the carbon block). Tufts of cotton wool are fitted in each of the seven holes. These tufts, when in position, press on the carbon diaphragm D which is of thin carbon, 2 1/4 inches in diameter and 40 mils thick. A sort of sleeve of soft felt, F, fits over the edge of the carbon block, and is also pressed against the diaphragm D by the heads of six bronze springs, which are all joined together at the centre, and clamped with the carbon block. Six recesses are made in the latter to allow the springs to work freely. The carbon block and screw S are otherwise insulated from the case by a mica washer , M, and bush, H, and by an ebonite washer , W, at the back. Rings of blotting paper, P, are used to clamp the diaphragm, and they also serve to clamp in front a membrane of oiled silk, E, which prevents the moisture of the breath, etc, reaching the diaphragm. An ebonite or soft rubber funnel fits into the recess R. About five grains (by weight) of carbon granules, G, are put in the recess left at the back of the diaphragm. "

For its time this was a very advanced and well-refined transmitter. The carefully manufactured design stayed in production with only minor changes until the introduction of bakelite handsets in the 1920s.


The basic models of the series were

AC100 The "Turret" phone, described above.:

AC110: Skeletal with lightning arrestor on the ebonite deck. Four terminals on the earliest models, later increased to five. The fifth terminal was generally unused, but some manufacturers added a peg to hold an extra earpiece and the fifth terminal was used to connect this. After this model the lightning arrestor was moved to the terminal block. The old catalog number was 375. It was produced up to about 1912.



Left: Early lightning arrestor on the deck







AC120: As above, with a pushbutton to short out the bells while give a stronger ringing signal, and with the line terminals fitted under the deck. This is the most common Australian model. 4 terminals and a pushbutton on the deck .


Left: Lightning arrestor moved to the terminal block.






AC130 As above, without the bell cutout switch on the deck - this was included in the sliding cutout switch at the end of the generator shaft.As the generator handle was turned, a spiral machining on its shaft pushed out the cutout switch and broke the bell contacts.

AC140: As above, with modified wiring to put the transmitter and receiver in parallel, instead of in series. This allowed the phone to still work in a limited fashion even if the transmitter or receiver failed. In previous models the failure of one of these components meant the whole phone was inoperable. The line terminals were on the edge of the deck. British Ericsson Model N2000

AC200: With a crank at each end of the generator and the handset mounted across the axis of the phone. This allowed the phone to be used from either side of a desk. It is rare. Old catalog number is 385. An extended peg to hold a separate earpiece could be provided on the end opposite the crank if required. This was wired in series with the main receiver.




Basic AC120 circuit diagram, Australian Post Office 1914.

This diagram shows the APO's preferred wiring with the transmitter and receiver wired in parallel
















1. Steel Deck


An "emergency" version with a stamped and folded steel deck, turned wooden handset grip and generator handle, and without teardrops was briefly produced after the end of the First World War. The serial numbers of the known examples show them as being made in 1919. The deck is slightly smaller than the usual ebonite deck, with no room for a ringer cutout switch. The cutout function is provided by a sliding switch on the magneto shaft. In most other respects the phone looks like a standard skeletal. Photos from Australasian Telephone Collectors Society Newsletter, May 2003

2. Crank

Although the crank was usually held on by a small nickel plated nut that covered the end of the shaft, some have been noted with a basic hexagonal nut to hold the crank. This left some of the threaded end of the shaft protruding. The reason for this is unknown, and there is insufficient data on serial numbers to suggest if it was an emergency WW1 measure or just a production shortcut. The example shown is on an Australian phone.

Although it might seem that the exposed shaft would be a danger to the user's knuckle, in practice it does not seem to be a problem.











3. Conversions

Apart from the model variations listed above, the phone also received some conversions from the telephone companies who used it.

The Australian Post Office modified the tele No. 2 by fitting a condenser to allow use on CB exchanges.

Although the generator and ringer were inadequate for rural party lines, the APO also modified the Skeletal for use on urban party lines. It was listed as their Telephone No. 4.







Dial conversions have been made to the Skeletal, but most of these appear to be unofficial. It is, after all, a magneto phone, and such conversions would seem pointless. In spite of this, modern "reproductions" exist in large numbers with inappropriate pushbutton dials fitted to make them workable on modern exchanges. Most of the one-off conversions mount the phone on a wooden plinth, and mount the dial in an appropriate adapter at the front of the phone. At least this doesn't damage the phone.




4. The National Telephone Company of Britain was a major buyer of Ericsson phones from the late 1890s. They ordered 100 000 phones from Ericssons and they gradually customised the Skeletal into a major variant. The noticeable differences in this variant are the lack of teardrops on the cradle, and the "antique bronze" or black finish instead of the usual nickel plate. The transmitter shown on this example is a version introduced in the late 1890s. Some early phones were fitted with white rubber feet.

The National was Britain's largest phone company and their maintenance workshop at Beeston complained that the teardrops were easily broken or lost (they were mounted onto the balls at the end of the crosspiece by very fine threads that stripped easily). Ericssons left out the teardrops for them, and this probably reduced the cost per unit as well. Some phones were finished in a dark oxidised brass finish rather than nickel plate. It cut costs and allowed the phones to be refurbished with a gunmetal black lacquer. These modifications were adopted by the British Post Office when they bought out the National and kept on using the phone.

The oxidised finish in a variety of shades was also widely used by the Beeston factory when it was bought out by Ericssons.





5.: Handset.

The National was also responsible for a very common change to the handset. They originally used telephones bought from the Bell Telephone Manufacturing Company in Antwerp, Belgium. When they changed over to Ericsson phones they still had large stocks of usable Bell / Western Electric handsets, which they used to repair Ericsson phones. This practice was also followed by the British Post Office and many other European administrations.The handset is fitted with a very early capsule-type transmitter.

The practice may have been the result of a complaint from Mr Dane Sinclair, the Chief Engineer of the National, that the Ericsson transmitters did not work properly with the National's Western Electric switchboards. This seems quite likely, as British Ericsson later obtained a license to produce Western Electric's Solid Back transmitter to fit to their British telephones. Mr Sinclair was a highly competent engineer, and the number of Skeletals throughout Europe fitted with WE handsets indicates that he may have been right. The exact nature of the problem, though, is unknown. It could also have had something to do with the conflict between the Ericsson transmitter and the patents of Edison regarding carbon transmitters. The National held the British rights to the Edison patents on behalf of the Bell company, and may have been reluctant to get involved in patent disputes. Using WE handsets would have been a simple way to sidestep the issue. Some of these phones were fitted with a ringer on which the striker operated vertically, rather than Ericssons' horizontal striker. The origin of this bell motor is unknown but the rest of its design appears to be Ericsson.


Other Companies

Now let's look at some of the variants produced by other companies, using Ericsson parts. In most cases they bought in the base unit from Ericssons then added their own handset and/or cradle. Many of these variations date from around the First World War, when supplies were disrupted.


A B Telefonfabriken, Sweden

From Stockholm, produced from 1896 to about 1902 when the company was bought out by Ericssons. It was initially produced by SAT because Ericssons was having trouble supplying phones in quantity. It is practically a direct copy of the AC110 apart from the generator cover, cradle and pillar. Three slightly different versions were made. Production continued briefly after the Ericsson buyout with the final production around 1905 (?).

The phone is better known as the "Tunnan" or "Drum" because of the shape of the cover over the generator. The drooping cradle appears to be typical of their telephones, and served to give the phones a lower profile than the Ericssons. In later years some of their phones were modified with a dial fitted to the centre of one side to make them automatic.

An earlier version did not have the drum cover and looked like a standard skeletal, but was still fitted with their distinctive cradle.



A/S Elektrisk Bureau, Norway

An interesting adaptation of the AC100 from Norway's local manufacturing firm. Around 1889. Elektrisk Bureau was a general Norwegian electronics manufacturer, and produced a number of phones with elaborate decoration. They produced their own designs and also copied Ericsson phones.





Berliner, Germany

c. 1900. Emil Berliner did most of his telephone work in the United States for the Bell company. A transmitter he developed for them was only briefly put into production, partly due to patent problems and partly due to it being replaced by the cheaper Blake. He received his U.S. patent finally in 1892 and at this time he also patented it in some European countries. He formed a company in Hanover to put it into production.

This phone uses an Ericsson Skeletal base and generator, and what appears to be a Western Electric handset modified to take his transmitter. It was used in a number of countries but never seems to have achieved large production numbers.





This 1902 Berliner model seems to be almost completely Ericsson except for the unusual rearrangement of the magnet legs and WE receiver and the lack of bells. The awkward bends in the Ericsson legs must have been difficult to produce accurately, so this appears to be an attempt to produce a less complicated copy of the style.







British Post Office


This is the BPO's tele No. 14, a curious adaptation of a skeletal base and a separate transmitter and receiver. Since the skeletal phone's main design feature was the handset, it is hard to understand why this phone should have been produced. The ornate design of the switchhook suggests that it was designed and built for the BPO by Ericssons, but there do not appear to be any records to support this.

Photo courtesy Bob Freshwater






Deckert & Homolka / Ericsson, Vienna


Apart from the unusual transmitter, whose origin is unknown, and the solid gearwheel, this telephone is almost completely AC110. From about 1900 to about 1915.

They also made a version with a leg/magnet assembly similar to the Berliner shown above.




Kopsch, Germany

This small German firm briefly used the Ericsson base, but all the upper parts are of their own manufacture. Little is known of their history.






Peel Conner, Britain

Late 1890s to around 1919. Their phone is substantially Ericsson during the days when the Peel Conner factory was part of GEC, but during the years when Peel Conner was a separate company (1910 to 1921) it has a solid brass gearwheel (sometimes with circular holes rather than spokes), and the crosspiece on the cradle is Peel Conner's distinctive turned drum shape. Note also the bus bars in the centre of the terminals leading down to the bells and to a peg for an extra earpiece. The tops of the cradle are fitted with metal balls, rather than the usual rounded-off ends.







Reiner, Germany

This Munich company produced telephones over a long period, and this very early example uses some parts of their own manufacture combined with a mostly Ericsson frame. It shows the Reiner receiver. c. 1899 - 1903..







Rikstelefon, Denmark

The Danish telephone company Rikstelefon was supplied with many Ericsson and part-Ericsson telephones from Kungliga Telegrafverket, the government body that controlled telephony in Denmark. Telegrafverket used Ericssons telephones extensively, although they fitted them with their distinctive handset. They also had a preference for the simplified cradle - only their earliest phones use the ornate Ericsson cradles and handsets.

Kungliga Telegrafverkets Model No. 5 used the old cradle, and No. 6 used the basic cradle as shown with sliding switch ringer cutout. No. 7 seems to have briefly gone back to the elaborate Ericsson cradle, with minor wiring differences, but the exact difference is unclear. From about 1900.



Sterling Telephone and Electric

This British company briefly sold the skeletal unmodified, and later fitted with a solid gearwheel and a peg at the other end for an extra earpiece (Model 390). They also mounted the phone on a plinth fitted with intercom switchgear, their Model U480.








Stocker, Germany

From Leipzig, this telephone is almost standard Ericsson except for the unusual single bell and the extra cradle mount set at the top of the pillar. From around 1920.






Telefongyar Reszvenytarsasag, Budapest

This partly-Ericsson company in Hungary produced this unusual and distinctive little telephone for the state telephone administration. It seems to have successfully compressed the Skeletal into a more compact phone. The generator sits lower so there is no room for bells underneath. These and the coil would be in a separate bellbox. Note that the handset is Western Electric - whether this is original or a maintenance replacement is unknown. 1902-1915. The phone is also known branded Deckert-Homolka.





Welles, Germany

About 1900. This phone is based mostly on Western Electric parts as used in their Eiffel Tower. The handset, cradle and pillar and the generator are WE. The magnet assembly is Welles' own production. The final telephone looks a bit like a skeletal, although it appears to be mostly a local composition using many outside-sourced parts from Western Electric instead of Ericsson.






Australasian Telephone Collectors Society Newsletter, various.

L M Ericsson catalogs, Sweden and Britain, various

Mirz, Peter "Skelett-Telefone , Gerateubersicht fur Sammler" December 2003

Kungliga Telegrafverket - Apparater M M 1906 (Electronic copy from Project Runeberg, Lars Aronsson 1997)

Poole J "The Practical Telephone Handbook" London 1912.


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