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KX-T206E good for kids' intercom with UK GPO 706, 746?

Started by ashley, June 21, 2013, 08:39:17 AM

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Hello all...

I recently bought a box of five old rotary phones (UK GPO 706 and 746 units, I believe), hoping to make an intercom (local only, no external connection) to amuse my technically-minded 4yo son and friends.

I am a computer systems engineer by training and have experience meddling with digital stuff, but I'm a bit out of my depth with the analogue nature of these things.

I read several brilliant posts here about Panasonic 308 units from eBay, and that seems like the easiest way to set up a fun system for us.

But perhaps a second hand Panasonic KX-T206E might be better for our situation though: it seems a little smaller, and I'm hoping a little cheaper.  For example:

I'd appreciate some advice.  I'm attaching an installation manual I found for the 206.

  • Would a Panasonic KX-T206E work with our rotary phones?  (I'm thinking: make voice communication possible, ring the bells, allow extensions to be dialled.)  I see no mention of "loop disconnect dialling" in the manual, but perhaps it'll work anyway?
  • I think I saw a post about resetting a 308 to factory settings on this forum, but I don't see any similar feature for a 206 in the installation manual.  If I buy a second hand 206, is there a risk it might be configured into a state which won't work for us?
  • The manual says (p20) I can use a conventional touch tone phone for system programming, so I'm hoping that I can get away without buying a proprietary telephone (eg KX-T7130).  But the manual does warn that I'll lack a display in that situation, so won't be able to check any settings I've made.  Might that be a show-stopper in practice?
  • I'm thinking of putting the PBX and a few phones in our house, but also putting two phones in my son's playhouse.  This is a wooden shed (without power) in the garden about 5 metres from the house.  Is it safe to run a cable (presumably containing 2 pairs) to the playhouse, or should I be thinking about lightning protection and other safety measures?

Any thoughts appreciated!



Looking at the instructions myself, under the "Specifications", section 5 mentions Dialling, and internal accepts Tone dialling and Dial Pulse, so it will accept Loop Disconnect dialling... :)

A system phone to do initial programming is a useful thing to have, but if it's not going to be used for phone lines, it's easier just to reset it to default and use as-is as you probably won't need the additional features anyway...

Now, looking again at the instructions, you need proprietary connectors to hook up the extensions and phonelines, rather than standard RJ11, if those connectors are missing, the 206 may be a bit more difficult to wire up than a 308 or 616... :-\

Also, if the GPO phones are converted (though personally I wouldn't let young children use such things as toys, knowing what I was like as a kid, it'll end up in pieces, and if they ring the phone when it's opened up they'd get a 90v shock if they were touching the wrong part of it!!), you will need to use Master sockets on each extension to make them ring, though you can cheat by using surplus ADSL filters (especially if you upgrade to a BT Iplate and have a load of them things left over) as they basically act like a PBX Master socket (adds a ringing capacitor to the line), which is handy) so you only need to use a single pair of wires for each extension... :)

And as for fitting telephone wire outdoors, well, there is a risk of lightning regardless of how you put it in place, personally I wouldn't want to use anything that is connected up to the household wiring, though people do have outdoor offices, so I guess they must have buried cable in shielded conduit, I don't know how you'd go about fitting that though... ???


Ah, thank you twocvbloke... that's very helpful.

I've only looked inside one of the phones so far.  It is unconverted (compared with it lacks the conversion resistor).  None of the phones have plugs on the cable ends... some just have cut ends, some have 4 spade connectors with white, red, blue and green wires.

I didn't realise the Panasonic 206 had proprietary connectors.  That's a nasty gotcha... thanks for pointing it out.

Actually, I'm starting to think back to my starting point with this, which was here:

I can certainly build the simple circuit shown there, which connects two phones, a resistor and a 12V power source in series, allowing voice communication.

But ideally I'd like multiple phones (perhaps 4), and I'd like the kids to be able to activate the ringers somehow.

There is a comment on that page by Nuno.S.Almeida aimed at solving this.  The suggestion is "Connect all the phones in parallel. Connect a ballast (yes, a fluorescent tube ballast coil) in series with the DC power supply (12V should work) and power all the phones from there."  I've drawn up my understanding of that as a circuit diagram below.

This apparently would let the kids talk on one common voice line, and ring all the phones by dialling '0' (the commenter says "The pulse dialing shorts and opens the ballast, which will produce enough high voltage to ring the bells").

But... I'm far from understanding this circuit.

  • Would this really work?
  • For the "fluorescent tube ballast coil", could I use eg Maplin MW09K: a 65W starter, shown at
  • Presumably I could leave the phones unconverted?
  • Does it matter which way round I connect the phones?

I guess you could still get a shock from touching an internal phone component whilst the phones are ringing, but I trust my son to follow "unplug before tinker" instructions, at the moment anyway.


It's a bit beyond me too to be honest, I'm sure there's people on here who could explain such a system... :D

Personally though I'd just recommend getting a decent PBX like the Panasonic KX-T308 for them to play with, that'll take up to 8 phones, or if that 206 has it's connectors included (ask the seller to be sure), that would work too, it's just that "if" that is the issue, buying a PBX is a lot simpler than figuring out the wiring for that battery powered setup... :)

As for the phones themselves, if they're unconverted then you can use them as 2-wire phones, as they usually have their capacitors left in place to get them to ring, you just have to connect the red & white wires to the PBX (via whatever wiring you put in place) and join the Green wire to the White wire (easier to do this inside the phone by joining terminals 17 and 18 together, as they swapped the Green & Blue around in later 700 models), that saves the need to use master sockets... :)


Thanks again!  I bought a 308 on eBay last night and will report back with how we get on... :)


Oh dear... I'd read about the symptoms but thought I had immunity.  I think you are right: I'm currently afflicted by the pleasant delusion that we need four rotary phones in the playhouse, and another four in the house for maximum playability :)


Quote from: ashley on June 24, 2013, 08:39:31 AM
Oh dear... I'd read about the symptoms but thought I had immunity.  I think you are right: I'm currently afflicted by the pleasant delusion that we need four rotary phones in the playhouse, and another four in the house for maximum playability :)

Aren't the kids going to get any to play with too?   ::)



(Well... full disclosure... have two 746s working fine, one 706 with non-functional ringer, one 706 with non-functional dial, but I'll meddle with those a bit later...)

Thanks again for the help, twocvbloke.  I joined the terminals and made the connections as you suggested.

I'll post some pictures once I get this set up in the proper location.

It's not just me enjoying this: son has had a play... he's much amused, especially by the ringing sound.  He doesn't quite have the concept of taking it off hook before dialling yet, but it'll come.  Right now, he's enjoying the cardboard box that the PBX came in :)


Quote from: ashley on July 01, 2013, 12:54:37 PMone 706 with non-functional ringer

Inside that 706, does it have a large metal can (either clipped to the base or mounted to the PCB, depending on which version it is)? If it doesn't, it won't ring, and may have transmission issues as it's a 2-in-1 capacitor (one side for the ringer, the other side for the transmission), they were removed from scrapped phones as they apparently contained nasty chemicals called "PCBs" (not to be confused with Printed Circuit Board), whether or not that is true is debatable, but they removed them anyway!! :D

If it has got that in place, it may not be wired up correctly (e.g. wired for Plan 4 use, which connects the ringer in a different way), or the capacitor or the ringer coils may be faulty... :)

To check it's wiring, see this diagram:

It may look a bit daunting at first, but all the connections are labelled as per the terminals on the board/base, so once you visualise it you can wire it up no bother, and it's only Fig.1 (Telephone No. 706F) that you need to look at... :)


I've got a KT-TA 616 (will upgrade to 624 when I have about 4,000 pennies for the upgrade card) and am wiring in an amplifier to the paging output so I can do "Control calling Ashley, please dial 43 from any extension"