GPO Double Current & Single Current keys.

001......This rare GPO Double Current (Non-Reversing) Key with Send/Receive switch, dates from about 1860. The serial number is GPO 6. Used for transmitting morse code over land lines in the 19th century.
  • Mike / M0DVO adds: "This type of key is a Double Current Key, but achieves the polarity change by swapping between two batteries which have commoned opposite poles".


    002...... This classic style GPO Double Current Reversing Key has the grand glass round top. c 1906. The double current key is known as a reversing key - used to reverse the current when signalling.
  • Dennis Goacher / G3LLZ informs that there are Mark 1, 2 & 3 keys. (Mk 1 from 1885). The mark one has a glazed top to the cover and Capstain terminals (later ones had cheese head terminals). The mark 2 has a solid brass cover and cheese head terminals, and the mark 3 has a solid cover and milled terminals. (This could vary enormously as parts were sourced during production or replaced during servicing). Keys for the military usually had solid covers and were stamped somewhere with a broad arrow, however, the GPO used a broad arrow ID too (thanks to George Saunders for that info - Oct 2010).

    Key Drawing. Above is a drawing showing the contacts and general layout of a typical Double Current Reversing key.


    Circuit Diagram. Here is a view of the setup of the typical circuit with both keys set to Recieve. Note the addition for each station of batteries, relay, galvanometer and a sounder.


    009. .....A key here with no serial number, Nickel Plated for use in the colonies.


     
     
     
     
     
     

    010......A fine key made by H. White & Co. 1918.


     
     
     
     
     
     

    011. .....GPO Single Current Increment Key. (Very rare Development key).

    A 6 terminal key with serial number 0000. This type of key is known as a Single Current Increment key - a key used for altering the strength of the current in a Quadruplex system. Note the six terminals in all and no Send/Receive switch.The glass topped cover is unusually held in place by two small screws. As this is a Development key with s/n 0000, it is extremely rare.


     
     
     
     
     

    011. .....Every part (there are over 90 parts making up this key), including nuts and bolts and small wood screws are stamped with the broad arrow. Obviously no expense spared on this marvelous key. The only parts not stamped are the three springs ! Even the knob made of horn is stamped with the arrow.

    This key is what Dennis Goacher describes as a "DEVELOPMENT" or "PATTERN" key. "The term Pattern Key refers to the time when a key assembled to the correct tolerances was made available to the instrument makers as a reference standard, against which any parts made or repaired could be compared. An early form of quality control." Dennis Goacher.

  • QUADRUPLEX EXPLAINED

    Quote from Dennis Goacher G3LLZ: "From the early days of telegraphy a need arose for increasing the capacity of the lines connecting the stations, the final result for morse telegraphy being the Quadruplex system in which two messages are simultaneously sent in each direction, making four messages in all along the same wire". "The principal used to differentiate between the two sets of signals that are going in the same directions, that one set is transmitted by means of Reversed Currents (double current working), and the other by changes in the strength of the currents (single current working). The receiving instruments are such that one set is polarised and responds only to changes in the direction of the transmitted currents, whereas the other set is non-polarised and responds only to changes in the magnitude of the currents, being indifferent to changes in direction". Dennis Goacher.


     


     
     
     

    053.....This fine scarce GPO FHB-53 Key with Send/Receive switch, was the successor to the big double current keys.The key itself was made by Signalling Equipment Ltd. England, and designated the model: Type "F-17"


    "BK"