Interest in Nixie tube clocks has gained momentum in recent years with modern designs paired with new old stock (NOS) tubes from the ex Soviet block or Mullard – Philips nearer home. You may be interested in the history of the first Nixie digital clocks or at least the first available in the United Kingdom back in the nineteen sixties…
Darang Ltd, manufactured digital systems including logic modules, timers and clocks in the 1960s. Their factory was based in Hackbridge in England not far from Mullard’s vacuum tube and transistor factory in Mitcham, Surrey.
The black cased Digicron model, pictured below, went on sale in 1965 and offered both 12 and 24 hour digital time displays. Consuming 25 watts, the clock used the 50Hz mains supply as a frequency source – common for most synchronous electro-mechanical clocks of the period. Originally priced at £90, this was an expensive clock and provided a space-age style for the home at the time. Darang also produced a six digit version to display seconds that cost a little more.
The design utilised Mullard’s ZM series nixie tubes for the front display along with GTE trigger tubes inside for the decade counters. Like nixies, trigger tubes also used neon gas to strike between anode and cathode with the addition of an auxiliary cathode or keep-alive and the trigger electrode. With suitable voltages, two red glows are maintained in the tube, one between the anode and auxiliary cathode and the other between the trigger and cathode.
Trigger tubes suffered from reliability problems, as I well remember, and any mains interference could add the odd minute or hour to an otherwise accurate display. I must have played for hours as a kid trying to set the clock to the right time!
Darang Black Perspex Nixie Clock
This photo was taken from an advert that appeared in Practical Electronics October 1965. The clock also featured in the media at the time. I don’t have any examples of these clocks now all were discarded in the seventies when LED displays took over.
Later in 1967, Darang developed a new Digicron version aimed at the industrial market. This digital clock still used nixie display tubes and the decade counters were replaced by semiconductor logic driven from internal time source offering far greater accuracy and better stability. A larger 30mm nixie tube was used for hours and minutes along with a smaller 15mm for the seconds.
Darang Digicron Nixie Clock
Various models were produced including oven controlled crystal oscillator time sources along with date and day indicators. Claimed accuracy of the oven controlled time sources was two parts in a million. Power consumption increased to 35 watts.
A brochure with details of the Six-Seventy clock is available below.
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