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Old 18th Feb 2016, 4:52 am   #1
Earlofdon
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Default Old GPO Office Telephone

Recently found this old gem.

Is it possible to rewire it in order to get it working again?
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Old 18th Feb 2016, 12:07 pm   #2
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Default Re: Old GPO Office Telephone

Looks like it, see here: http://www.britishtelephones.com/plans625.htm
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Old 18th Feb 2016, 3:32 pm   #3
Dave Moll
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Default Re: Old GPO Office Telephone

Yes, I have one of these plansets, wired up to a second 700-series telephone via a six-core cable, with a buzzer and non-latching button in the extension telephone for signalling between the two units. I supply the power for the buzzers and indicator lights from a PP9 battery. As I recall, the link given above by Bill is what I used to work out the connections for my planset.

Does it have the original cable and terminal box attached? If so, this simplifies connection.

I look forward to hearing how you get on.
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Old 18th Feb 2016, 6:01 pm   #4
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Default Re: Old GPO Office Telephone

It's covered by diagram N625, which is on Sam Hallas's site. There are, IIRC, 3 versions of the internals, the earliest one used transistors to sense the line current, but to improve reliability (!) these were replaced by a reed relay on the later versions.

It can pretty much be wired to a normal 2 wire line as-is, but that will not use the extra functonality. It can be linked to one or two extensions, you can call an extension from the main planset, or vice versa and have local communications between the planset and an extension.

IIRC, having 2 extensions is called 'Plan 105', having one is 'Plan 107'. You want to look at diagrams N4507 and N4509 respectively.

There are actually 2 versions of each. One is known as 'internal' (in the same building) and uses multi-core cable between the planset and the extensions. The other is 'external' (IIRC several miles of cable between planset and extensions), this needs a special 'ringing converter' covered in diagram N626. This is hard to find, and even harder to copy, there is a special transformer and the relay is 'slugged'. If you to figure out the schematics in the N diagrams for the external versions you will be puzzled (IIRC there appears to be no path for the ringing current) until you realise that the 'a' side of the line is earthed at the exchange.

Wiring for internal extensions is therefore a lot easier. The extension is a 700 series telephone fitted with one or two momentary buttons (to call the 'main' or the other extension) and a DC buzzer. You also need a 12V or so DC supply for the buzzers, lamps (in the planset) and to power the speech circuit in intercom mode. There was a GPO power unit for this (53B?) or if mains was not available, 12V from dry cells. Originally 8 of those 'Flag' cells. For testing/demonstrations, 8 D-size Duracells work fine and last several months.

In theory the extension can be a Trimphone, the DC buzzer was then mounted externally. Officially you can only fit one switch to a Trimphone, but the switch 'flap' unit can be modified very easily by cutting the actuator in half and adding a second microswitch. Never done officially, but I did it to prove it would work.

You can also use something like an LST4 (Loud Speakng Telephone), not surprisingly gven that many LST4's were used by company executives, many of the ones that turn up were Planset extensions and still have the right buttons and buzzer fitted.

My experience is that the hardest part of this is finding the extra bits (switches, buzzers) for the extensions. If all else fails you can make up a little box to sit next to the extension telephone with normal components.

I have a Planset and have wired it (for demonstration purposes) on all possible extension plans. Please PM me (or post here) if you need any help.
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Old 18th Feb 2016, 8:19 pm   #5
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Default Re: Old GPO Office Telephone

that phone takes me back to primary school. The secretary had that one and the headmistress had the extension.
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Old 18th Feb 2016, 8:28 pm   #6
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Default Re: Old GPO Office Telephone

You took the words out of my mouth.
It was exactly the same with me. I was fascinated with the fact it had the extra buttons. The headmistress demonstrated it for me which probably started an interest in telecommunications - an interest but absolutely no technical knowledge!
It was this memory which stirred me to buy the 'phone.

In my haste to submit the original posting I omitted to say that I haven't the faintest idea about telephone connections/circuits/straps etc.
I've managed to remove the bottom of the 'phone/Planset and in the process have opened a tin of worms (well wires).
Can somebody very kindly advise what if anything I need to disconnect and connect etc?

Many thanks for the kind replies - much appreciated.
Chris.
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Old 18th Feb 2016, 8:44 pm   #7
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Default Re: Old GPO Office Telephone

That's a Mk3 Planset, the latest version. The reed relay I mentioned is the long metal cylinder at the bottom right of the picture. The Mk3 uses that 'continental cradle relay' rather than a GPO type used in the Mk2.

Looks like the strapping is right for internal extensions.

If you just want to put it on a normal line, try connecting the like (pins 2 and 5 of the normal Plug 431A (BT telephone plug) to the black and blue wires in the 18 wire line cord. If you have the original Block Terminal (junction box) that's terminals 4 and 6.

It does, of course, have a 1k bell, so will appear to have an REN of 4. If you have other
telephones on the same line, you should remove the strap at the right hand end of the top row of terminals in the planset (in your picture) and replace it with a 3.3k resistor.

I think if connected like that, it will ring on incoming calls, but you will have to press the SPK TO EXCH key to answer or make a call.

If you want to use it 'properly' and have internal extensions, etc, then you really need to get the diagrams I mentioned and wire according to them. It's rather too much information to put in this sort of reply.
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Old 18th Feb 2016, 9:27 pm   #8
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Default Re: Old GPO Office Telephone

how I remember sitting in the office wiring a couple of these up to install in the early 1980's. I think I still have a buzzer for one somewhere as well
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Old 18th Feb 2016, 9:33 pm   #9
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Default Re: Old GPO Office Telephone

Hi,
I obtained a Planset some years ago and had it working in two places that I/we lived in, after constructing a unit with a couple of relays and a transformer from an old VCR to supply 40 volts ringing AC to allow a standard "modern" PST (Plug and socket) telephone with earth recall to be used as the extension instrument.

Some years later I re designed my circuitry which used a transistor to provide the recall signalling and used buzzers situated in the extension line jacks, this was never pressed in to service but worked well at the "prototype" stage.

If you (or anyone else) would like the details of either of my designs please feel free to send me a PM.

On a nostalgic note the primary school I attended had a Planset 625 and at some point one of my friends, whose after had a building business, had a Planset fitted in their shop premises with the "B" end being the phone in their home wired as an external extension to Plan 107. Many years later my first place of employment also had a Planset with an external extension to a warehouse in another village some two and a half miles away.


Regards

Andrew
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Old 18th Feb 2016, 11:41 pm   #10
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Default Re: Old GPO Office Telephone

Chris,
Do you want to use it as a Planset, or just as a normal telephone?
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Old 19th Feb 2016, 12:11 am   #11
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Default Re: Old GPO Office Telephone

Just as a normal 'phone as we have cordless handsets in every room so no need for extensions.

Would be nice to have the buttons illuminating though
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Old 19th Feb 2016, 2:47 am   #12
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Default Re: Old GPO Office Telephone

Quote:
Originally Posted by TonyDuell View Post
That's a Mk3 Planset, the latest version. The reed relay I mentioned is the long metal cylinder at the bottom right of the picture. The Mk3 uses that 'continental cradle relay' rather than a GPO type used in the Mk2.

Looks like the strapping is right for internal extensions.

If you just want to put it on a normal line, try connecting the like (pins 2 and 5 of the normal Plug 431A (BT telephone plug) to the black and blue wires in the 18 wire line cord. If you have the original Block Terminal (junction box) that's terminals 4 and 6.

It does, of course, have a 1k bell, so will appear to have an REN of 4. If you have other
telephones on the same line, you should remove the strap at the right hand end of the top row of terminals in the planset (in your picture) and replace it with a 3.3k resistor.

I think if connected like that, it will ring on incoming calls, but you will have to press the SPK TO EXCH key to answer or make a call.

If you want to use it 'properly' and have internal extensions, etc, then you really need to get the diagrams I mentioned and wire according to them. It's rather too much information to put in this sort of reply.
Thanks Tony,

Do I need to completely disconnect all of the connections inside before making new connection or do I connect to the existing cable?
I have a new conversion cable as pictured, is that ok?
Apologies for the questions but I haven't a clue!

The existing cable is still connected inside the 'phone but not at the other end.
Also can I connect a battery in order to light up the switches?
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Old 19th Feb 2016, 4:15 am   #13
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Default Re: Old GPO Office Telephone

Quote:
Originally Posted by AndiiT View Post
one of my friends, whose after had a building business, had a Planset fitted in their shop premises with the "B" end being the phone in their home wired as an external extension to Plan 107.
If only that was possible nowadays!

I'm to open a small office a couple if streets away from home. Having such a set-up would actually be so much better than having a separate line in the office.
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Old 19th Feb 2016, 9:18 am   #14
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Default Re: Old GPO Office Telephone

Looking at the state of the existing cable, it's probably simplest to remove it and replace it with your "conversion cable".

Looking through my notes, it would appear that for two-wire working (i.e. using the internal ringing capacitor rather than the one in a master socket) you need to make the following connections to the terminals in the planset:

6 - A-leg of line cord (white)
4 - B-leg of line cord (red)
1 - negative terminal of battery
2 - positive terminal of battery

Leave the green and blue leads in the line cord unconnected (best to wrap them in some insulating tape).

I would need to study the instructions to see whether there is a simple way to disconnect the internal ringing capacitor and make connection to the one in the master socket (blue lead of the line cord). I will also check whether there are any spare terminals in the planset where unused line-cord lead(s) can be parked.

Please note that the down side of using the internal capacitor of the planset is that dialling from it can cause bell-tinkle on other 'phones connected to the line. If the rest of your installation uses electronic ringers (i.e. your cordless system described), this may not be a problem.
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Old 19th Feb 2016, 10:54 am   #15
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Default Re: Old GPO Office Telephone

Thanks again Dave, will have a bash at it later on today.

As a point of interest, how on earth is it possible to connect one of these to an extension miles away? (as mentioned in an above post)
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Old 19th Feb 2016, 11:53 am   #16
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Default Re: Old GPO Office Telephone

I take it you are referring to an "external extension", which would require the availability of a dedicated line if the extension is remote from the site of the main unit. It would also require additional hardware (ringing converter) to create the signal to ring the bell in the extension.

An external extension could also be on the same site as the main unit, and has the advantage over an internal extension that it only requires a single pair (plus signal earth) for connection once the signalling equipment is installed.

If at some time you wish to add an extension (or two) locally, it is probably easier to wire them as internal extensions. The only hardware needed then is a buzzer and non-latching switch (which are less difficult to obtain) for installation in the extension 'phone, though three pairs are needed between the extension and main unit to carry the voice and signalling. As I said in an earlier post, this is the setup that I have.
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Old 19th Feb 2016, 12:06 pm   #17
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Default Re: Old GPO Office Telephone

Quote:
Originally Posted by Earlofdon View Post
As a point of interest, how on earth is it possible to connect one of these to an extension miles away? (as mentioned in an above post)
Un the 'old days' it was done by renting a pair of wires - only the GPO/PO/BT had the right to run cabling external to your property. Then in the 1980's you were able to run your own cabling (subject to wayleaves) between two properties whose curtilages were no more than 200 metres apart. That has now been extended to an unlimited distance again subject to wayleaves. Occasionally there were in the old days, the odd private circuits such as the old open wire overhead pole route which followed the Vyrnwy Aqueduct from Lake Vyrnwy in North Wales to Liverpool but that was built by being included in the Act of Parliament for building the pipeline. You don't need to go that far. You can now achieve it using the Internet provided you have Internet access at both ends. But using the Planset N625/Planphone A which is set up with an external extension (Diagram N4509) really needs a physical pair plus you'd also need a Converter Ringing No 9A to call the extension.
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Old 19th Feb 2016, 3:16 pm   #18
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Default Re: Old GPO Office Telephone

Quote:
Originally Posted by Dave Moll View Post
1 - negative terminal of battery
2 - positive terminal of battery
Whoops! Those are the terminal numbers for the terminal block that would be at the far end of the existing cable - clearly a "senior moment" on my part. Inside the planset, they are, respectively, 16 and 20. 4 and 6 in the terminal block are connected to 4 and 6 inside the planset, so what I said there is correct.
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Old 19th Feb 2016, 4:14 pm   #19
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Default Re: Old GPO Office Telephone

Quote:
Originally Posted by Dave Moll View Post
I would need to study the instructions to see whether there is a simple way to disconnect the internal ringing capacitor and make connection to the one in the master socket (blue lead of the line cord). I will also check whether there are any spare terminals in the planset where unused line-cord lead(s) can be parked.
Having done so, I can't see a straightforward way of separating out the connection to the bells to use an external ringing capacitor. Also, as far as I can see, there aren't any spare terminals on which to park the unused leads of the line cord.
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Old 19th Feb 2016, 8:16 pm   #20
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Quote:
Originally Posted by Dave Moll View Post
4 and 6 in the terminal block are connected to 4 and 6 inside the planset, so what I said there is correct.
Thanks for that.
So I connect the battery to 4 and 6?
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