(Louis Meulstee’s web site)

Home Fullerphone principle Using the Fullerphone Superposing Various models Utel Electronic Fullerphone

Various models and variations

Next page (German Utel) Fullerphone Italian model.

Fullerphone Mk.III, No. 13039, manufactured in 1920 by W/T Factory WD, Teddington, S.W. (above)

In Germany and Holland the Fullerphone was called 'Geheim Telegraaf' (Secret or Secure Telegraph). Later developed electronic versions are dealt with in a separate section.


'Apparado da campo per telegrafia inintercettible - Mod 1931'. (Apparatus, field-telegraph, non-interceptable - Model 1931) The Italian Army copied the Fullerphone in the early thirties. Its circuit was similar to the British design, though there was no line balancing adjustment potentiometer provided.

- Fullerphone Trench ‘D’ and ‘F’. The Trench D was a converted D Mk.III telephone with an external 1,5V call and speech battery, connected by flexible leads. The Trench F was similar but fitted in a wooden case.

- Fullerphones Trench ‘S’ and ‘W’ were similar in design having just minor wiring changes. Electrically they were quite similar to the Trench D and Trench F but differ in mechanical construction.

- Fullerphones Office Mk.I and Mk.I* were fitted with the potentiometer and reverse current switch.#

- Fullerphones P.O. Types Marks 234 and 235, were produced by the Post Office. #

- Fullerphones P.O. Types Marks 237, 237a and 273b were produced by the Post Office.

- Fullerphone Mk.III was developed towards the end of World War 1. It remained in production until the late 1930s.

It should be noted that no signals were heard in the receiver (headphones) when the key was pressed in the types marked #.

Fullerphone Mk.III

The Fullerphone Mk. III (left and right) was developed in late World War 1. It was the standard model in the inter-war years, until being superseded by the Fullerphone Mk. IV which became available in about 1937. A telephone and calling buzzer facility were fitted in the Mk.III model; these were of course liable to overhearing. Note the folding type Morse key in the bottom right hand corner of the case. This model was fitted with a potentiometer and reverse current key. The main instrument was mounted in a canvas covered wooden carrying case, provided with a protective lid.

Fullerphone French TM 1932. Fullerphone French early model.

French Army Fullerphones.

Early French Fullerphone (left). No type number is known. It was superseded by ‘Parleur a l ‘ampe TM 1932’ (right).

Fullerphone Mk. 6 (right) was a fully tropicalised version, enclosed in an immersion proof metal case. The Fullerphone itself was almost similar to the Mk. V. Note the use of Headphones type DLR No. 5.

Posted in this section is a variety of different models and patterns of Fullerphones. The use of British Fullerphones and manufacture of similar instruments in other countries, notably France, Italy,Portugal, USA, Germany and Holland is noted.

Fullerphones produced and used in other countries.

Fullerphone Office Mk.I*. (Above and right). This model was manufactured in 1916 by Siemens Bros. The Morse key was fixed-mounted on the control panel along with a reverse current switch and potentiometer.

Fullerphone Mk.III. Fullerphone Mk.III with accessories. Fullerphone Mk.I *

World War 2 models.

World War 1 models.

Fullerphone Mk.IV* (right) was a slightly modified Mk.IV incorporating radio filtering to reduce interference and the possibility of radio interception.

The Fullerphone Mk.IV** (not shown here) was similar to Mk.IV* but fitted with a crash limiter.

Fullerphone Mk.IV* (right) produced by Northern Electric Co. in Canada. Earlier production instruments had a Canadian Key W.T. 8 Amp No. C2. Later manufactured Canadian Fullerphones were fitted with Canadian Key W.T. 8 Amp No. C3 (as shown in the drawing right).

Fullerphone Mk. IV * modified to Mk. V (right). The key in this photo was an early Key W.T. 8 Amp No. 2.

Fullerphone Mk.IV, Mk.IV*, Mk.IV**, Mk.V and Mk.6.

Boxes, No. 1, Fullerphones, also known as Mk.I case, was for use with headphones with a metal headband.

Boxes, No. 2, Fullerphones, also known as Mk.II case, was for use for headphones with a canvas headband.

In 1935 the “Fullerphone Experimental” was developed, based on the Fullerphone Mk.III. It was much lighter, smaller and had a modified and replaceable buzzer. The telephone facility, which was incorporated in the Mk.III was omitted as being liable to be used in a forward area by a non-technical user, under the impression that the speech from it could not be picked up by the enemy. This experimental model evolved into the Fullerphone Mk.IV.

The most commonly used Fullerphones Mk.IV, Mk.IV* and Mk.V were housed in an aluminium and steel case, secured by guides in a wooden carrying case provided with a sling.

The headphones were carried in the lid of the case (Mk.I case only) or in the Fullerphone case (Mk.II case). When the lid was completely closed, the ‘Pull-On’ switch was automatically set in the ‘Off’ position. A spring stop which kept the Fullerphone unit in position in the carrying case had to be pressed down for the unit to be drawn forward into the operating position. A second stop prevented the unit from sliding completely out of the case. The removable Buzzer F slide into position on the top right-hand side of the instrument, the connections being made by three contact springs.

The Mk.IV* was fitted with radio interference suppression and to reduce the possibility of radio interception. A crash limiter was fitted in the Mk.IV**. Mk.V models were similar to the Mk.IV** but had a tropical finish. The Morse key was a Key WT 8 Amp No. 2 which could be one of the many versions which were produced over the time. The Morse key of the Mk.V and Mk.6, however, was a Key Signalling No. 2, tropicalised, which was similar in appearance to Key W.T. 8 Amp No. 2 Mk.II. It had contacts not made from the usual Tungsten but from different material which was more suitable for tropical use. These contacts could, however, not handle 8 Amperes, hence the different name and YA class VAOS stores number.

Apparently all Mk. IV, Mk.IV* and Mk. IV** models were enamelled black . The later issued Mk. V and Mk. 6 models were usually light-blue/grey.


In 1942 and 1943 Canada produced 14.000 Mk.IV and Mk.IV* Fullerphones. The instrument differed only in detail to the British parent model and was functionally and physically similar. The Morse key fitted in the later produced Canadian Fullerphones was a Canadian Key W.T. 8 Amp No. C3 which was a simplified version with two U-shaped bridges of pressed steel construction.


The headphones used with the Fullerphone were low resistance types. Three models are recorded to be issued: Receivers, headgear, CLR, double Mk.III (used with Mk.I case);  

Receivers, headgear, CLR, double No.3 and  Receivers, headgear, DLR, double No. 5 (used with Mk.II case).

Fullerphone carrying cases.

The Mk.I case (left) was principally issued with the Fullerphone Mk.IV and early Mk.IV*. When not in use the headphones (Receivers, headgear, CLR, double Mk.III, having a metal headband) were held in a bracket in the lid of the carrying case.

The more widespread used Mk.II case (right) was issued with later Fullerphone versions and used headphones with a canvas headband and a metal neckband (Receivers, headgear, CLR, No. 3 and DLR, No. 5) stowed inside the case with the neckband inserted behind the buzzer housing.

CLR= type ’C’ Low Resistance

DRL= type ’D’ Low Resistance

Fullerphone Mk.III removed from its carrying case.


The ‘Sutel 40’ (an abbreviation of Summer-telegraph 40) was a German version of the Fullerphone where the buzzer-chopper was replaced by an electronic valve. Summer-telegraph actually translates to ‘Buzzer-telegraph’.

It replaced the WW1 pattern ‘Utel’, a German equivalent of the Trench Fulllerphone. A detailed description can be found in the Electronic Fullerphone section

Fullerphone Mk. V  (right) was issued from mid World War 2 onwards and a tropicalised version of the Fullerphone Mk.IV**. The principle circuit changes were the use of Buzzer F Mk.II** which had the coils wired in parallel and Key, Signalling, No. 2, tropicalised.