Home:  Exchange Equipment: GPO EXCHANGE OR MASTERCLOCK, 1960's


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Pendulum clock used in telephone exchanges, for timing functions.
Item A0357 is the relay unit for this.
Using the Hipp toggle principal which swings the pendulum by pulling it every so often by a magnet powered by electric pulses, supplied only when the momentum of the swing started to die.
This unit uses a modified version of this system.
Matthaeus Hipp in 1838 is reported to have invented the toggle in a dream, at a very early age. He got up and drew it immediately. This is almost certainly fiction.
This item is working in the museum and running six clocks.
See http://www.electric-clocks.nl/clocks/en/page04.htm for the history

Your comments:

  • This is very similar to the master clocks London Transport used for timing on the signalling system as well as operating the station clocks. Due to problems with the contacts these were replaced by a lamp and photo diode and a board of early electronics. I believe this also drove the electronic circuits that divided down the time into days.
    .......... John Murrell, Carshalton, England, 7th of February 2020

  • Known as a GPO clock 36 and used to drive slave clocks and control STD call metering equipment
    .......... Malcolm Holt, Eaton Socon, St Neots, 29th of March 2013

  • I bought a clock identical to this from the Post Office "Preston" Telephones exchange in Bavant Road Brighton when the 1927 "Siemens 16" exchange was decommissioned in the 1970's. It was made by the Goblin Company of Leatherhead in Surrey. I presented it to the local Leatherhead museum in 2005.
    .......... Don McBeth, Ditchling East Sussex, 8th of January 2011

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