TELEPHONE No. 72

Candlestick, Strowger Automatic System

It's a standard table telephone made by Automatic Electric in Chicago, probably assembled over here from piece parts at the Edge Lane factory of ATM in Liverpool. 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).

The Telephone No. 72 has a Mercedes dial, a stepped bottom part made of brass, and an electro-magnetic receiver. Circuitry is pure Chicago and not customised for Britain. It also has no induction coil and just uses a simple DC series circuit with the transmitter and receiver in series with the dial pulse springs. The receiver is shunted to stop tinkling, but NOT the bell! It has a bias spring to stop this, and the resistive part of the bell in series with a capacitor, acts as the spark quench for the pulse contacts!

The diagram for the Telephone No. 72 (Issue C) of the diagram (AT12) is dated November 1918 (The N diagram is dated December 1919).   The Telephone No. 72 was superseded by the Telephone No. 124 when the Dial No. 8 was adopted as standard in Nov 1922 (according to Engineer in Chief's diagram  'Misc 623 - Automatic Telephones, Existing and Proposed Dial Spring Assemblies and Telephone Circuits' - dated 17.9.24)   Diagram states 'used at all ATM Co's exchanges until adoption of Telephone No. 124 in Nov 1922'.

Known down under as the Geelong phone as exactly the same phones were used at Geelong in 1914 (first auto exchange in Australia).

Last revised: August 12, 2006