Help wiring an old GPO 600/700 series phone

[NewOrder]

I am not sure exactly what model it is but I would guess its from around 1970-1980 it has three wires on the cord, one brown, one white and one green. What pin numbers do I need to connect these to on a BT plug? I have been told it has been converted to work on modern systems but the plug had snapped off. My customer insisted it worked in her house less than ten years ago. I have a few doubts about if it has been converted or not.

So firstly what is the wiring code and secondly what is the worse that will happen if it has not been converted to a post 79 system?

 

[bernardgreen]

To convert the phones internal strappings and change the bell from low impedance to high impedence start here

http://web.ukonline.co.uk/freshwater/pstconv1.htm

Note the comment in red near the top of the page.

I cannot recall if this page warns about how in-correctly modified phones can disrupt the other phones on the line. And not all exchanges will accept loop disconnect dialling recognising only DTMF

 

[blondini]

Those old phones were built to last! Done a few conversions in the past when plug & socket first came in. Always worked ok with a 3.3k resistor on the bell. Just follow the guide for '706, 710, 741 & 746' in the link that Bernard posted to check the straps and fit a new linecord.