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Old 30th Aug 2018, 8:58 pm   #1
scottyb
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Default British Telecom C2 klaxon and control box

Hi,
Iíve recently acquired an old British Telecom Klaxon compete with a cast iron control box fitted with a mercury switch and PO3000 type electro magnet relay. What I want to know is if itís possible to use this system as an external ringer for my phone. Somebody told me it might not be possible as the phone system is different to what it used to be. The unit has 4 coloured wires entering into it, green goes to an earth point on the cast iron box, Brown is not connected to anything, and orange and blue are connected to one terminal each on the PO3000 relay. I assume that the relay is activated when an incoming call is detected, putting a voltage through the relay which in turn tips the mercury switch setting off the Klaxon. What I need to know is if itís possibly to wire in to my phone system and if so, which wire goes where?
Thanks, Scott
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Old 31st Aug 2018, 12:10 am   #2
Pellseinydd
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Default Re: British Telecom C2 klaxon and control box

The GPO circuit diagram is N1291 Hopefully that will help - be careful as it usually involves mains wiring. The Klaxon is the 'Hooter No 2. The Hooter 2A or 2C are mains operated whilst the other Hooters No 2B and No 2D are DC hooters. The ringing current on a PSTN is still the same as it has been since many years ago so should still work. Hope you're some distance from your neighbours ?
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Old 31st Aug 2018, 5:05 am   #3
TonyDuell
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Default Re: British Telecom C2 klaxon and control box

Remember that when this device was in use, extension bells were connected in series, whereas now they are connected in parallel.

I'd try connecting the relay coil (orange and blue wires) with a 2k2 (or a 1k if the former doesn't work) in series between terminals 3 and 5 of the modern socket. If the telephones still ring and the relay operates then all you need to do is wire up the mains side.
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Old 31st Aug 2018, 12:05 pm   #4
scottyb
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Default Re: British Telecom C2 klaxon and control box

Thank you very much for the replies. Some great info there. I’m going to give this a go when I get a moment. The property is pretty remote so it won’t bother anybody else!

I must admit, I’m a bit of a novice on this! I’ve had a look at my main box in my house and it appears that there are 2 sets of leads coming in to my house. One set it connected to a standard 4 pin female telephone plug and there is also a separate female plug for the internet?! Any ideas?

Thanks in advance
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Old 31st Aug 2018, 6:45 pm   #5
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Default Re: British Telecom C2 klaxon and control box

Hi guys, ignore the last message, thanks to your info Iíve managed to get it working, and you were spot on, a 2K2 resistor was perfect for the job. All working a treat. Thank you again!
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Old 2nd Oct 2018, 4:12 pm   #6
Brigham
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Default Re: British Telecom C2 klaxon and control box

I first met these Hooters in Norfolk boat-yards. There was sometimes something odd about the way they operated.
The one I particularly remember only hooted every other pair of rings. Anyone heard of such a thing?
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Old 2nd Oct 2018, 5:45 pm   #7
dseymo1
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Default Re: British Telecom C2 klaxon and control box

As I recall, that's normal operation, at least for those I knew many years ago.
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Old 2nd Oct 2018, 7:51 pm   #8
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Default Re: British Telecom C2 klaxon and control box

I remember one of these used for the 999 trace phone. idea was to let every one know a 999 call needed tracing and it then became a race to answer the phone and trace the call. it was so loud it could be heard down the high street. the phone line was a normal number so people in the know could ring it and see who could run the fastest.
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Old 3rd Oct 2018, 10:41 pm   #9
60 oldjohn
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Default Re: British Telecom C2 klaxon and control box

I seem to recall mains powered Klaxon's were banned after a GPO or BT engineer was electrocuted. We have a very loud klaxon here that is powered by only the phone line.


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Old 3rd Oct 2018, 11:19 pm   #10
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Default Re: British Telecom C2 klaxon and control box

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Originally Posted by 60 oldjohn View Post
We have a very loud klaxon here that is powered by only the phone line.
Bedlam Tonecaller? Made by Hosiden Besson? They use a rocking armature receiver and exploit the resonant frequency of operation by driving it at this frequency into a little exponential horn. They're bloomin' loud! Try putting together a rocking armature receiver, and 9V battery and a 555 oscillator around 1.5kHz with the receiver pointing downwards onto a hard surface with about a 1cm gap between and hear the difference it makes.

Re: the klaxon thing... When I was at British Steel in the '70s some of the PAX extensions in noisy environments were fitted with dark green ironclad relay boxes manufactured by the A.T.M. Company, which contained a similar relay, and would drive either a mains hooter or operate a light in sympathy with the ringing cadence.

The GPO Klaxon units I have seen - outside only - are mounted in a larger rectangular iron box which presumably has a physical barrier dividing the mains equipment relay contacts from the telephone ringing voltage.
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Old 4th Oct 2018, 8:52 am   #11
Brigham
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Default Re: British Telecom C2 klaxon and control box

How is it arranged to ignore every second ring?
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Old 4th Oct 2018, 9:12 am   #12
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Default Re: British Telecom C2 klaxon and control box

Does it simply hoot like an American phone, not dropping out between the double ring or does it literally ignore every other ring-ring?
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Old 4th Oct 2018, 9:13 am   #13
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Default Re: British Telecom C2 klaxon and control box

Quote:
Originally Posted by Brigham View Post
How is it arranged to ignore every second ring?
The diode across the relay ensures that the back-emf maintains the relay on during alternate half-cycles of ringing current, and so doesn't chatter. I built a similar arrangement in lieu of a telephone bell for our works PAX once.

But if it's a relay with a heel-end slug on it, it'll be slow to release in any case and the further delay may cause it to miss the second ringing cadence.
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Old 4th Oct 2018, 5:10 pm   #14
Brigham
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Default Re: British Telecom C2 klaxon and control box

It hoots twice, same as an ordinary ringer, then it misses out the next pair of rings, and hoots twice for the next pair.
A 'loaded' relay would be one way to do it.
Any ideas about how the GPO did it? I was always curious to find out what the ringer in the actual telephone instrument did, but I never manage to be in the office when it rang.
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Old 4th Oct 2018, 7:49 pm   #15
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Default Re: British Telecom C2 klaxon and control box

I know where there is such a relay and klaxon (redundant) but I'd need to be in a certain place at a certain time to answer your question!
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Old 4th Oct 2018, 7:52 pm   #16
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Default Re: British Telecom C2 klaxon and control box

I note the 'N'-diagram states that a choice of relay exists for continuous signals and discontinuous signals. The relay in the 'N'-diagram is shown as a normal relay, not a slugged one. So perhaps a slugged one is the other option?
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