GPO TRIMPHONE

The Trimphone was introduced in 1965 as a fashionable alternative to the standard telephones available from the Post Office, The name is an acronym  for Tone Ring Illuminator Model, referring to the innovative electronic ringer tone ("warbling") and the illuminated dial. The luminous dial contained the mildly radioactive element tritium. Concerns amongst the population forced the manufacturer to remove that feature. The volume of the ringer gradually builds up over the first few cycles.The Trimphone was available in three two-tone schemes: cream,  blue and green with the handset in the darker colour. The first keypad version appeared in 1977. Early keypad versions used relays to generate pulses, later versions had transistors for either pulse dialling or two tone dialling. By 1980 there were 1.6 million Trimphones in use in Britain out of a total telephone population of 27 million.