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The Synchronome ‘company’ was formed in 1895 by partners Frank Hope Jones and George Bennett Bowell and set up premises in Clerkenwell, the clock making centre of London. Initially the company was not a success and Bowell left in 1899. He later designed the Silent Electric clock, set up the Silent Electric Clock Company and with which he remained connected until the 1920s.

Hope Jones and new partners re-established the Synchronome Company Ltd in 1912. In the years up to 1905 synchronome developed a series of early master clocks progressing incrementally towards the final design of the Synchronome switch and associated detached gravity escapement that formed the basis of the great majority of their clocks in the 20th century.

The development of the Shortt free pendulum clock in the early 1920s, the most accurate clock of its time, made Synchronome into the preeminent UK electric clockmaker, despite strong competition from Gents and others.

The company declined after the Second World War and after various changes in ownership it was merged into Tann Synchronome and vanished when clock production ceased in the early 1980s.

Clocks and timekeeping products

Synchronome made or sold too many products to list but the following is an outline, and many of these items have information or photographs available on this website.

  • Early master clocks before 1905, half seconds, three-quarter seconds and second pendulums many of which are recognisable by a rectangular shaped brass backplate. These are scarce.
  • The standard Synchronome master clock, with numerous minor variations after 1908, made in three-quarter seconds and one seconds pendulum, earlier examples in ‘architectural’ cases
  • The ‘triangle movement’ clocks with one second pendulum, made between about 1915 and 1921
  • Clocks in the Coventry series made after between 1928 and 1939 in Coventry with serial numbers prefixed with C. Minor differences from the standard series.
  • Clocks after 1908 could be fitted with seconds indication and various types of seconds switch
  • Clocks with an output to drive external power grid metering equipment
  • The Mark 2 Synchronome, made from about 1963 with a movement that was simpler to manufacture
  • Synchronome also made Post Office number 36 and number 46 clocks for the UK Post Office, based on the designs of the Silent Electric Clock Company
  • The minute master clock, made by Synchronome and other companies from after about 1960
  • The quartz ‘time check’ master clock
  • The Horophone, an early system for receiving wireless time signals
  • Many different designs of slave clock for dials up to 3 metres in diameter
  • Bellringers and programmers; slave clocks driving rotating discs with holes for pins to trigger switches
  • Inertia bar observatory regulators
  • The Shortt free pendulum clock
  • Mains driven synchronous clocks
  • Marine master clock systems capable of being adjusted forwards and backwards in time.
  • Watchman recorder systems
  • An alternate polarity clock system designed by Westerstrand.

In addition, Synchronome clocks were made by the Australian Synchronome Company


British patent no 1587 of 1895 Hope Jones and Bowell The double gravity escapement

British patent no 7868 of 1897 Hope Jones and Bowell Improved double gravity escapement

British patent no 6066 of 1905 Hope Jones The earliest electromagnetically reset gravity arm patent by synchronome

British patent no 1945 of 1907 Cunynghame and Hope Jones. The basic synchronome ‘switch’ patent

British patent no 18405 of 1909 Hope Jones. Locking slaves

British patent no 12,328 of 1911 Shortt The inertia bar regulator

British patent no 9527 of 1915 Shortt The triangle regulator

British patent no 187,814 of 1921 Shortt The hit and miss synchroniser

British patent 323,001 of 1928 Hope Jones Sympathetic pendulum system

British patent no 362,848 of 1930 Hope Jones. Magnetic free pendulum clock

British patent no 463,087 of 1937 Hope Jones. Mechanical free pendulum clock

British patent no 521,775 of 1940 Hope Jones. Synchronising via synchronous motor

British patent no 893,991 of 1960 Burgess/Synchronome. Silent alternate polarity slaves

British patent no 894,267 of 1962 Burgess/Synchronome Master clock variable impulse

Serial numbers

The standard master clocks can be approximately dated from their serial numbers. Numbering started in 1908 and reached 1000 by approximately 1922, 2000 by 1935, 3000 by 1947, 4000 by 1951 and 5000 at around 1955. The mark 2 clocks were separately numbered starting in 1961 and rising to approximately 6000 in the early 1980s when production finished.

Clock markings

The information is included here because the clocks are so diverse. It will be included in the subfolders.

Power supply.

The standard Synchronome is designed to run on 3 volts for clocks with no pilot dial or 4.5 Volt for clocks with a pilot dial. Three D size cells will run a master clock without slaves for up to 2 years.

The standard Synchronome produces single polarity impulses every 30 seconds to drive slave dials. Synchronome slave dials each contain a resistor as spark suppression, so the master clock can drive a series circuit with quite a lot of dials without risking sparking and destruction of the master clock contacts.  However, running many slaves in one circuit will require a high voltage.  All circuits should have suitable fuses.  A maximum of 15 dials is suggested as sensible based on a 24 Volt system.  Beware using Gents or other slaves as these have no internal spark suppression.

Some later slaves ran on 24 Volt alternate polarity impulses, notably the Westerstrand based system.

Restoration and repairs.

The usual items to be missing are the gathering wire arm and jewel and the suspension spring. Dimensions for both of these are included in ‘Synchronome: Masters of Electrical Timekeeping’ noted above, which also contains information about servicing movements. Spare newly made gathering arms and other spares may also be found on eBay. Synchronome movements do not require a diode for spark suppression, there is a resistor concealed behind the movement casting.

Practical tips

Synchronome clocks do make a distinct clunk every 30 seconds as the gravity arm is reset. This can be minimised by ensuring that the damper pads are not compressed and the clock is well-adjusted. Filling the air space between the case and the wall with a foam or similar material to stop the case acting as a sound box is also very helpful and the case must be securely fixed to the wall. Running the clock on the lowest possible current also reduces the noise. In a domestic environment these clocks would be considered noisy, however they are much less noisy than a Gents C7 but noisier than a Gillett and Johnston master clock. A standard clock should be capable of keeping time to within a few seconds a week.

The gathering jewel is particularly fragile and it is best not to advance the clock by turning the NRA lever to the A position. Unless carefully adjusted the jewel may hit the catch and fracture.

In the standard 1 second clock the rating nut changes the rate by 30 seconds a day for one full turn. In clocks with a weight tray on the pendulum rod, adding 0.67 g increases the rate by one second a day.

Slave circuits should be run on constant current. With the clock contacts closed at steady-state 330 mA should flow through the circuit. This is approximately equal to adding 1.5 V per slave dial, depending on the wiring and size of the slave dial movement.

Three-quarter second pendulum clocks are slightly less reliable and are more sensitive to incorrect adjustments.

Buying and selling

The early Synchronome clocks are rarities and only seen at auction or in museums. Clocks made after 1920 are relatively numerous and can be found for sale in local auctions in the UK, Europe and the US and on Ebay. Clocks from the 1940s and later are sold at very reasonable prices.

When buying it is worth remembering that Synchronome sold parts for clocks and encouraged amateur clockmakers to build their own, so not everything that looks original is. In general, amateur clocks are not nearly as well made as the commercial clocks and less collectable. They can be recognized because either they have no NRA plate on the left of the movement or, if they have one it lacks a serial number (except ¾ second clocks).

Three-quarter second clocks are much rarer than the one second clocks, having been made for only a short period.

Sources of information

The definitive source of information on Synchronome is Bob Miles book ‘Synchronome: Masters of Electrical Timekeeping’ published by the UK Antiquarian Horological Society and now in its second edition. This provides history, lavish colour illustrations and photographs of almost all types of clock and a very useful chapter on restoration and servicing. Includes many references to further sources of information.


A further source are the books written by Frank Hope Jones himself; Electric Clocks and Electrical Timekeeping. Both provide detail on how the clocks work and how the movement was developed. Searchable pdf copies of these books are in the Clockdoc documents folders and original and facsimile versions are readily obtainable from internet sellers.

More detailed technical information about individual types of clock can be found in the published lectures by Hope Jones in various journals of the time

There are two Synchronome related internet discussion groups at

This website has a range of Synchronome related documentation including advertisements wiring diagrams and technical information, all in the documents section.

The electrical horology group of the antiquarian horological society UK has one of its Technical Papers on set up and maintenance information that can be found here *** insert link***

Last updated 8.12.19 author EWO

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