746 again. Confusion. - UK Vintage Radio Repair and Restoration Discussion Forum

Diabolical Artificer · 27th Nov 2011, 1:02 pm

I have a GPO 746 model 'phone and am trying to wire to modern BT socket.
T4 + 7 are strapped as is T8 + 9, but T16 + 17 are strapped and 18 + 19; do I strap this last pair together?

The ringing coil has a resistance of 1,034 K do I put a resistor from T4 to the coil?

Lastly, does the 'phone need earthing (green lead)?

Many thanks,
Andy.

Dave Moll · 27th Nov 2011, 2:42 pm

If you look at http://www.britishtelephones.com/pstconv1.htm (under 706, 710, 741 an 746), you will see that what you need is:

3.3K resistor between T4 and T5
strap between T5 and T6
blue line cord lead to T6
NO strap between T6 and T7
red line cord lead to T8
green line cord lead to T15 (spare - no, you don't need to earth)
strap between T16, T17, T18 and T19 (i.e all four connected together)
white line cord lead to T18

Diabolical Artificer · 27th Nov 2011, 3:40 pm

Thanks Dave.

Andy.

27th Nov 2011, 1:02 pm	#1
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,667	746 again. Confusion. I have a GPO 746 model 'phone and am trying to wire to modern BT socket. T4 + 7 are strapped as is T8 + 9, but T16 + 17 are strapped and 18 + 19; do I strap this last pair together? The ringing coil has a resistance of 1,034 K do I put a resistor from T4 to the coil? Lastly, does the 'phone need earthing (green lead)? Many thanks, Andy. __________________ Curiosity hasn't killed this cat...so far.

27th Nov 2011, 2:42 pm	#2
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,130	Re: 746 again. Confusion. If you look at http://www.britishtelephones.com/pstconv1.htm (under 706, 710, 741 an 746), you will see that what you need is: 3.3K resistor between T4 and T5 strap between T5 and T6 blue line cord lead to T6 NO strap between T6 and T7 red line cord lead to T8 green line cord lead to T15 (spare - no, you don't need to earth) strap between T16, T17, T18 and T19 (i.e all four connected together) white line cord lead to T18 __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

27th Nov 2011, 3:40 pm	#3
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,667	Re: 746 again. Confusion. Thanks Dave. Andy. __________________ Curiosity hasn't killed this cat...so far.