TELEPHONE No. 55


A.T.M. Co's wall set used on the Strowger Automatic System.  Fitted with an Electro-magnetic receiver.  This telephone can also be used on party lines.

It is the phone used by the GPO on the two auto exchanges introduced in 1912 (Epsom, Surrey and the Official Switch [i.e. Post Office Headquarters] in London).

Also known as the Epsom type.

Click here for more information on the Epsom exchange

Very basic circuit, with dial, Receiver Bell No. 4 and transmitter all in series with no induction coil.

Telephone No. 55A was wired to Diagram A.T. 200A and used with automatic subscribers having call meters.

The table equivalent is the Telephone No. 72.

Telephone Includes (Early type to Diagram A.T. 8B):-
1 x Condenser, MC No. 4.
1 x Cord, Flexible, 237.
1 x Dial, Switch, Automatic No. 1.
1 x Mouthpiece No. 8.
1 x Receiver, Bell No. 4.
1 x Strip Connection, No. 27.
1 x Transmitter No.11.

Telephone Mark 234 included (1918 diagram)
1 x Dial, Automatic No. 1.
1 x Bell No. 1A with bias spring.
1 x Condenser, MC No. 3.
1 x Receiver, Bell No. 4.
2 x Cord, Flexible, 116.
1 x Cord, Flexible, 222.
1 x Switch, Receiver No. 1.
1 x Hook, Receiver F.
1 x Transmitter No. 15.
1 x Mouthpiece No. 4.

Telephone included (1928):-
1 x Dial, Automatic No. 1 or No. 8FA.
1 x Bell No. 1A with bias spring.
1 x Condenser, MC No. 3 or No. 30.
1 x Receiver, Bell No. 4A.
1 x Switch, Receiver No. 1.
1 x Hook, Receiver F.
1 x Transmitter No. 1.

The Receiver, Bell No. 4A has no permanent magnet.  The American variant has a Diaphragm No. 9 and an Earpiece No. 4, whilst the Mark 234 has a Diaphragm No. 12 and an Earpiece No. 2.

Sometimes fitted to a Desk No. 4.

Telephones No's 55 and 55B were superseded by Telephone No. 105 or Telephone No. 121.

Circuit diagram - N155
Diagram - A.T. 8 (Telephone No. 55).
Diagram - A.T. 200A (Telephone No. 55A).


Paster Diagram

 

Here is a picture of the insides of a later Telephone No. 55.  All the brassware should be black and note the non-ATE dial, especially the way it is fixed!


Wiring for use in the UK

You are warned that this telephone has a very basic transmission circuit which is nothing like the quality of a modern telephone. The wiring is also non-standard and may tinkle bells on your premises, when dialling out.

  1. Red of new line cord to Terminal 1.
  2. Remove any link between Terminals 2 and 3.
  3. Insert 3.3k resistor between Terminals 2 and 3.
  4. White of new line cord to Terminal 2.
  5. Connect the Rectifier Element across the earpiece terminals.  If the phone goes faint then remove the it.

 

 
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Last revised: August 23, 2021

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