Quote:
Originally Posted by winston_1
RJ11 is an American plug and is not the one you want. You can buy leads though with spades to a BT plug.
Instructions are here. I don't bother with the 3.3K resistor and leave the link as it does not do what people think. It is suggested by those that don't understand the difference between impedance and resistance
https://telephonesuk.org.uk/conversion/ |
The reason for the resistor is simple. On the GPO system , phones ( other than a plan four- one permanently wired with a bell , where all phones had a plug and could be moved to other sites ) were speech in parallel and bells in series ( up to four 1000 ohm , resistive,in parallel, so the curent in bell circuit was V/( 4000-Jx). Now we've up to four phones in circuit , resistance drops to 250 ohm so the impedance ( resistance + inductive element has to be increased to stop ring trip . another reason for only having one capacitor in circuit is ring trip, another result of having two phone+ two capacitive bell circuits in parallel . So solution is simple - increase the inductive effect of 250 -x j to reduce the bell circuit current to that of V/(1000-xj , by adding a series resistor in bell circuit. ( x is inductive element = 2*PI*F*L)( where pi= 3.14, F= frequency of ringing and L= inductance of bell circuit).
And telephone guy- plenty of phone shops sell leads with a modern plug ( RJ ?) one one end. If yu still have the old phone cable, it's simple to cut the grommet off cable at where the it enters the phone by cutting across in parallel to line of cord and carefully priseing away and then glueing grommet to new cable. All you have then to do is plug BT plug into a socket and identify which wire goes where, solder terminals to the wires and connect. OR , cut the old cord and cut /solder and heatshrink to the new cable. Many of the old cables were copper with a plastic/ cloth inner . We found best way, was to strip a portion of sheath then remove another portion , slide this to end and tin the bit between, then cut off the end .