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TEL 42T/ATT or SONIC 70


The Sonic 70 telephone by GEC
by Alan Macdonald

A few years ago a telephone came my way and it sat in a box more or less untouched until last year when I started to take a bit more of an interest in it.  The telephone in question was made by GEC in 1968 or 1969 and the model was known as the Sonic 70.   I’ve tried a bit of research on the web and it seems that the most likely origin is the Post Office Telephone Instrument Development Group where it may have sat in “rogues gallery”.

From a cursory glance at the paster diagram, it is likely that the instrument would not have given satisfactory performance on all PSTN lines, so it may have been designed for the PAX market.  I’m therefore guessing that it was a ‘pre-production’ model of a ‘phone that never went any further.

Let’s move on now to the phone itself.

It appears at first glance to be an updated 700 series ‘phone, having used the standard No. 3 handset.  Although the TEL 40 brochure gives the colour as two tone green; my example is in the usual two tone grey.  The designer made a brave attempt at producing a modern look by coming up with a very angular shape with smooth lines.  The pressed steel base is upturned at the back to provide an anchor point for the line cord grommet; the front of the base is also folded up and forms the front of the casing. (fig. 1).  There is a carrying handle moulded into the case at the rear and GEC is impressed in silver just above the line cord grommet. (fig. 2). Some thought was put into the routing of the handset cord.  Rather than exit the case at the rear, the cord comes through a rubber grommet in the centre of the base, there is a clip on the base at either side and the user can choose which side they wish to have the handset cord appear.  Presumably this would help to eliminate those nasty tangled cords (fig. 3).

Fig. 1
 
Fig. 2
 
Fig. 3
 
Fig. 4

The handset uses the standard 4T receiver inset and a transmitter No 13 rather than the transmitter No. 16 I expected to see.  Other than that, the handset bears no further scrutiny other than to point out that the cord does not have a grommet fitted where it enters the case.

The base of the telephone is secured to the case moulding with four machine screws, each of which thread into brass inserts in the case.  Looking inside the telephone reveals a very simplified circuit consisting of just a bell capacitor (dated 1968), two resistors and an induction coil.  The bell coil is of the ‘uni-coil’ design and the bell gongs are of a much smaller size, being only 42mm in diameter.  The components and connections are all on a 14 way tag board, the components being soldered and all wiring using push-on connectors (fig. 4).  The switchhook springs bear a strong resemblance to those found in the 200 type telephone, having an open construction in what appears to be copper plated spring steel (fig. 5).  There is an eight-wire loom from the tag board to the switchhook springs and the dial.  The dial itself appears to be a standard No21 type but is fitted with a neoprene washer, then secured into a recess in the case with two machine screws rather than the standard method used by the PO.  The dial is also fitted with a clear plastic cover of a design I have not come across before.

Fig. 5

In conclusion it seems that GEC really did ‘push the boat out’ in trying to come up with a radical new design.  From the outside one has to admit that they did indeed come up with something new and modern looking.  This would certainly not have looked out of place in the modern office of the seventies.  Whether the internal design was finalised or merely presented as a prototype we may never know but to my mind the inside of this particular example looks ‘cheap and nasty’, so different from what we usually expect from GEC.

See also TEL 40

 
 
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Last revised: January 25, 2011

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