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.

Many were made in the USA by the Automatic Electric Company.

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

Also known as the Epsom type in the UK and the Geelong type in Australia (see APO Type 35).

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.

Because this telephone uses an electromagnetic receiver it is polarity conscious.  The positive of the exchange line is connected to terminal 1.

The 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 No. 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 No. 116.
1 x Cord, Flexible No. 222.
1 x Switches, 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 Switches, 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Telephones No's 55 and 55B were superseded by Telephone No. 105 or Telephone No. 121.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).

 

Circuit Diagram

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.  The line is also polarity conscious.

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 it.

Additional Pictures

Made in America

Internal view showing how basic the telephone is

Only three connections to the dial

Last revised: October 16, 2023