Can an old (1962) telephone be connected to a modern BT socket?

How strange -- I designed X.25 switches at GEC in the 1980's, and had to get those tested for PSS approvals in early days, and the line modules had to get electrical approvals. One I remember was our G.704 module which we designed to provide a raw unstructured 2Mbit X.25 link over BT's Megastream service. Went along to Baynard House, and the bloke took it and looked at it, and said "that's fine". It was the first G.704 module they'd seen, and they didn't have any tests defined for it!

Reply to
Andrew Gabriel
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Well the problem was that this was a product that had originated in the U.S.

For some reason, best known to themselves, BT had an addressing scheme (group number IIRC) that was 4, while in every other country it was 0. On this particular box the addressing wasn't configurable, simply because there was no need anywhere other than in the UK.

Anyway, the BT guy agreed to sign it off on the basis that I agreed that we would have a software fix to allow configurability before any were connected to their network. I suspect that he figured that if this wasn't there, it wouldn't work with their PSS environment anyway. All of the other HDLC and other tests had passed and they seemed more concerned about that for some reason. There was no interest in the hardware at all.

Imagine paying by the packet (well segment)..... but one did.

Reply to
Andy Hall

On Sat, 16 Feb 2008 00:15:16 +0000,it is alleged that Frank Erskine spake thusly in uk.d-i-y:

I usually use 3k3 and adjust the bell armature gap to 12/1000in to compensate for the lower power.

The 2x500 ohm coils were for hysterical... err historical reasons. The old CBS1 manual systems required the bell to be 250 ohm earth connected, and the CBS2/CB/Auto required 1000 ohm, so the 1A bell was designed with 2x500 ohm coils, and the 59A/B and C followed... such was inertia within the PO (why change it, it works), that it remained standard.

The much later (1979?) 59D bell did indeed have 2x2000 ohm coils, but I've never seen one wired parallel for 1000 ohm, although there's no reason it wouldn't work.

I think in some cases it was 5

ITYM To _allegedly_ maintain continuity ;-)

And of course American phones have a REN too... only it's not the same as our REN, what fun!

To the OP: Make sure you connect 2x 1N4001 or similar diodes in inverse parallel across the receiver (red/green in the handset cord on most GPO 300/700 series phones) to prevent acoustic shock from loose connections or dud dial offnormal contacts.. very likely in a phone of this age, as it can really hurt, and even cause hearing damage. Originally this would have been a metal rectifier with a lower forward voltage, but silicon diodes at 0.5-0.6v will still take the edge off the clicks and pops.

Reply to
Chip

Not too sure what you mean. PSS always required the DNIC to be present (2342), whereas most other networks only required the DNIC for calls to other networks. It was a bit like always requiring the full international number to be dialled for a phone call, even a local one. Actually, I thought this made a lot of sense. Generally there's no one typing in X.121 addresses for each connection (excluding dial-up PADs), so having short forms of addresses was just overhead in software to recognise (a bit of software I wrote a number of times in different products;-). Since we sold in other countries too, we had to cope with this though.

For the LCGN, PSS supported all 4 ranges if you subscribed to them, although BT stopped selling new PVCs around 1985 because their switches ran out of table space to record them. I can't recall if other country implementations supported multiple LCGN ranges (most didn't support PVCs, which would have removed one of the LCGN ranges in any case).

Reply to
Andrew Gabriel

You've stirred the cobwebs in the back of my mind on this one. I did mean LCGN rather than the X.121 addressing.

IIRC, BT had 4 for SVCs and lower numbers for PVCs. This was an SVC only product that went onto the market in about 1984 and in other countries SVCs started at 0 so there was no need to have setting of LCGN other than for the UK.

Reply to
Andy Hall

yes, same way as a new phone. Getting old cloth wire into an RJ45 is I assume impossible, so a modern plug with a short stub of wire is connected to the cloth cord.

This is an often misunderstood issue. REN of most old mechanical bell phones is 4. Phone exchanges are designed to guarantee all lines will power a total REN of 4. In practice most will power rather more, as the wire from the exchange's resistance is usually well below the limit, hence one old phone plus a couple of modern is not normally a problem, though it can be occasionally.

Most have built in caps and don't, but some do. Connection configurable phones can be connected up pretty much any way, and can be reconfigured any way. These configurables were designed to be usable as bugs too, phones were a reliable low cost way to bug people, and an engineer call to rewire the phone connection didn't arouse suspicion. So you might one day find a phone so wired, with mic across the line when on hook.

Why do you need diodes when there is already a metal diode stack in there doing this?

Finally if you dont like dialling the long modern numbers, you can use a handheld thingy to tone dial. Dials were fine in the days of 3 figure numbers!

NT

Reply to
meow2222

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Reply to
Frank Erskine

The nicest way is to terminate the 'cloth' cord on a bakelite Blocks Terminal screwed to the wall just as in days of yore, then have a short 'modern' cord from there to an adjacent NTE socket.

Reply to
Frank Erskine

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