Telephone 712L

This is an early version of the Trimphone and differs internally from the 722 version.

Above the dial we have the 20 way connection block, the numbering of the terminals is identical to that of the 706.  Above the terminals is the regulator, this is the standard regulator used in a 706.  Top right we have a stack of three 0.9uf capacitors two of which are joined in parallel to form the 1.8uf capacitor for the bell calling circuit. To the right of the capacitors is the induction coil, which again has been lifted straight out of the 706.

This instrument has been converted to work on the modern plug and socket system, and the original line cord and block terminal are stored.

The markings on the base tells us that this instrument was made Feb 1966 and is the model 712L.  We have no other information yet regarding the rest of the markings.  This Trimphone being a 712 would probably have been part a field trial and being prior to the final version, the 2/722, this makes it fairly rare.

The early Trimphones had an luminous dial, this was produced by a glass tube filled with a radio active material, which was located in a recess under the dial number plate.

The name TRIMphone is believed to be derived from the term ‘Tone Caller Illuminated Model’, however I have also been told that it was Tone Caller Interrupted & Modulated, either way the Trimphone was the first to have a tone caller in the UK.