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Old 21st Feb 2020, 12:04 am   #1
Nickthedentist
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Default GPO 706, when was the change from Diakon to ABS?

Hello everyone,

As many of us know, the GPO's model 706 phone, introduced 1959/60, was originally produced with cases made from Diakon (i.e. PMMA, poly-methyl-methacrylate, the same stuff as acrylic dentures are made from!). These don't seem to fade in the sun much, have a lovely "glassy" quality to them, but break easily if dropped. The difference is most obviously seen in the "ivory" coloured sets, the PMMA and ABS variantq looking very different from one another after 60-odd years.

Later, ABS was used instead, which was the material the later 746 cases too.

Does anyone know when this change took place? Was it with all the manufacturers? And were older, Diakon cases replaced with ABS when instruments were factory refurbished, as a matter of course?

Cheers,

Nick.
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Old 17th Mar 2020, 12:12 pm   #2
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Default Re: GPO 706, when was the change from Diakon to ABS?

Not exactly answering my own thread, but I've read on Bob Freshwater's site that you can tell the material used from codes moulded into the plastic:

12 = Diakon (PMMMA, Perspex)

17 = ABS


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Old 17th Mar 2020, 9:43 pm   #3
Nickthedentist
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Default Re: GPO 706, when was the change from Diakon to ABS?

More Googling has got me the answer... https://www.britishtelephones.com/t706case.htm

Ans. = very early 1963.

Last edited by Nickthedentist; 17th Mar 2020 at 9:52 pm.
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Old 24th Mar 2020, 2:54 pm   #4
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Default Re: GPO 706, when was the change from Diakon to ABS?

Quote:
Originally Posted by Nickthedentist View Post
More Googling has got me the answer... https://www.britishtelephones.com/t706case.htm
That's interesting, Nick.

My Ericsson N1901A PAX or export instrument very clearly shows a stamp 5/5 12 beneath the flat bit behind the handset rest and the thickness of the case suggests it's Diakon. But my 1961 Plessey GPO 706 Mk:2 instrument has a different marking, this time behind the front of the case below the dial, and it says BLD17, suggesting ABS. Yet the cases are the same thickness, feel and finish.

The marking inside the earpiece on the Ericsson is also 5/5 12 but on the Plessey is APB12 (A. P. Besson?) and a No:26, being, I think, the type of GPO designated earpiece.

Maybe early ABS cases were the same thickness as Diakon? It's like unravelling the Dead Sea Scrolls!
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