UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Plugging in extension causes main to ring

russell_w_b · 25th Feb 2021, 2:35 pm

Pretty sure it happens when there's a reversal of wire 2 and 5 at the telephone with the electronic ringer.

When you lift the handset of the 706 (or 746), the 12V d.c. passes from wire 5 through T18 and 19, one set of switch-hook contacts, the ASTIC, the regulator, the other set of switch contacts and out through Terminals 4,5,6 to Terminal 3 in the master LJU thence to wire 3 of the extension telephone cable.

But if the bottom of the electronic ringer is connected to wire 2 instead of wire 5. there'll be a direct current through it and it will hoot.

25th Feb 2021, 2:35 pm	#6
russell_w_b Dekatron Join Date: Jul 2007 Location: Penrith, Cumbria, UK. Posts: 3,687	Re: Plugging in extension causes main to ring Pretty sure it happens when there's a reversal of wire 2 and 5 at the telephone with the electronic ringer. When you lift the handset of the 706 (or 746), the 12V d.c. passes from wire 5 through T18 and 19, one set of switch-hook contacts, the ASTIC, the regulator, the other set of switch contacts and out through Terminals 4,5,6 to Terminal 3 in the master LJU thence to wire 3 of the extension telephone cable. But if the bottom of the electronic ringer is connected to wire 2 instead of wire 5. there'll be a direct current through it and it will hoot. __________________ Regds, Russell W. B. G4YLI.