Author Topic: new GPO 706 two tone  (Read 10042 times)

Offline Stephen Furley

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Re: new GPO 706 two tone
« Reply #45 on: September 12, 2011, 09:15:35 AM »


What it looks like from this side of the pond:

BT modular plugs & jacks appear to be more robust than RJ-11, with larger contact surfaces and with a tab that appears less likely to break off than ours.

Where I think BT went wrong was with capacitors in sockets and all that stuff: it would have been simpler to have one capacitor in each phone, with a bias spring on the bell, and then wire extension phones in parallel with no series element to the circuit.  The retrofits to obtain that result would have been easy.

But we have our own screwy wiring in the US too. 

The most frequent thing is when different wiring contractors use all data jacks throughout a building, and then wire them to different standards: T-568-A vs. T-568-B.  In that case, what would ordinarily be the 2nd pair on an RJ-11 jack, comes out as different pairs on the two different wiring plans for data jacks.  This has led to much confusion and merry chaos on more than one occasion.



I like the BT plug, but I think that for the sake of standardisation I'd have been prepared to go with the RJ-11.  There were several other countries which used them, I think Ireland and Gibraltar were two, but most later switched to the RJ-11, so we're pretty much on our own now.  The clips do sometimes break, but maybe not as often.  Our modular cordage is different to yours, slightly larger, more flexible, and sort of 'D' shaped, with one side somewhat rounded.  It still fits into a RJ-11 of course, it has to since that's what's used at the telephone end of the cord.  I prefer this style of cordage.   One of my crimping tools will do both types of plug, but will not do the left-handed type;  I've never seen a tool for those, and haven't seen the plugs listed anywhere for some years.

The idea of the capacitor in the master socket, rather than in each phone was to enable the telephone sockets to simply be connected in parallel rather than the series bell connections required by the old system.  Since the homeowner was going to be allowed to wire their own extension sockets a simple simple system was essential.  It  sort of made sense at the time, but it's a pain now.

Offline Stephen Furley

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Re: new GPO 706 two tone
« Reply #46 on: September 12, 2011, 09:25:23 AM »


Where I think BT went wrong was with capacitors in sockets and all that stuff: it would have been simpler to have one capacitor in each phone, with a bias spring on the bell, and then wire extension phones in parallel with no series element to the circuit.  The retrofits to obtain that result would have been easy.

On the 'new plan' socket system the phones are wired in parallel.

The capacitor and a test resistor in the master socket mean that, even with no phones plugged in, there is always a circuit across the line for testing purposes.

The master socket capacitor was seen as necessary to prevent bell tinkle on loop disconnect dialling. I don't think the GPO has ever used bell bias springs.

Also the surge arrestor in the master socket of course.  None of these components in a secondary socket.  Then there's the PABX master type that has just the capacitor I think.

Offline gpo706

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Re: new GPO 706 two tone
« Reply #47 on: September 28, 2011, 07:22:50 PM »
Had the bare naked lady, the key lock 746 and the charity, very dirty scabby phone, so I Frankenphoned them into one, the key lock didn't like the new spring hook so the body was taken and the key lock, then I tried the naked lady, the bells were loose and even when re-attached and rewired it didn't want to ring, so the cream charity job was rewired with a a dark grey cable, an on/off bell ringer switch and a neon ringing handset.

After much labourious work, it is now the charity chassis with the grey lock body and the flashing handset and bell on/off, the cute thing is it cuts the bells off at the switch but the neon still flashes, the last job is to get the key rewired to stop outgoing calls - later, will leave as it is till some further research.
"now this should take five minutes, where's me screwdriver went now..?"

Offline Owain

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Re: new GPO 706 two tone
« Reply #48 on: September 29, 2011, 03:21:03 AM »
the last job is to get the key rewired to stop outgoing calls - later, will leave as it is till some further research.

Shorting dial terminals D4 and D5 should prevent the loop disconnnect?