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Old 11th Jun 2012, 12:12 pm   #1
boombox
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Default 1920s Direct line telephone/intercom

Hi

I've bought an antique intercom.

My question concerns getting them working!

I have read that all is needed is a multi-core cable and a 9v battery.

Does anyone recognise this set (they look identical/similar to others I've seen on the interwebs) and could advise further?

Thanks!!
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Old 11th Jun 2012, 12:51 pm   #2
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Default Re: 1920s Direct line telephone/intercom

From memory (I'll check when I get home):

Z = 'Zinc' = negative of your battery.
C = 'Carbon' = positive of your battery.
L = 'Line' = one of your interconnecting lines.
MC may mean 'microphone and carbon', but I'll check on this.
ZE will be 'Zinc and Earth', so you'll need to connect your other interconnecting line here, along with your negative battery connection.

Polarity isn't important, but make them the same both ends. You'll just need a one-pair cable, or even one wire and earth to connect them.
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Last edited by russell_w_b; 11th Jun 2012 at 12:54 pm. Reason: Afterthought.
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Old 11th Jun 2012, 1:30 pm   #3
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Default Re: 1920s Direct line telephone/intercom

The same terminal labelling is found in the "telephones" section of the GEC catalogue of 1892. Different models use different combinations of the same set of letters, and the MC, ZE, C, and L configuration is only used on a "Hunnings Cone" model, made under licence form the NT Co.Ltd, which has two additional terminals B, B for a "detached bell". The wooden base looks just like that of the "Manchester Microphone" model, but this uses a different configuration of letters, and needed three cells. The "Hunnings Cone" Model was said to require "two agglomerate cells or two dry cells".
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Old 11th Jun 2012, 1:32 pm   #4
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Default Re: 1920s Direct line telephone/intercom

Thanks, Russell!

So would I need just one battery or two? I presume one. Can I use a standard 9v PP3 battery?

If so, essentially I would need four core bell wire. Two for comms and two for power.

I really hope the bell signalling works. I'm hoping it detects the off hook and signals the other unit on that basis.

Thanks again
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Old 11th Jun 2012, 1:42 pm   #5
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Default Re: 1920s Direct line telephone/intercom

Found some references:-

http://www.richardsradios.co.uk/hunnings.html

http://www.britishtelephones.com/gec/k040.htm
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Old 11th Jun 2012, 3:18 pm   #6
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Default Re: 1920s Direct line telephone/intercom

I would guess that it would have used one or two "Flag" cells (1.5V) in a separate wooden case. The main requirement is to be able to ring the bell, so you need to find the minimum voltage for this by experiment.
A close up of the circuit diagram might help.
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Old 11th Jun 2012, 3:36 pm   #7
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Default Re: 1920s Direct line telephone/intercom

Ooh - I've got a pair of those. They were in my grandparents house in London when they moved in (1940s). The previous owner was a doctor, and the phone was used for his secretary to let him know a client was waiting. I had them working when I was about 14, but haven't tried since. Mine don't have the labels on the terminals though, which made it more difficult!

I seem to think I had a 1.5V battery at each end, but can't be sure.

Rich.
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Old 11th Jun 2012, 6:10 pm   #8
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Default Re: 1920s Direct line telephone/intercom

This confirms my earlier post.

Old english telephone connections are:
ZE = Zinc and earth (negative of battery and earth, or return line).
C = Carbon (positive of battery).
MC = Microphone carbon (being the carbon in the microphone).
L = Line.

You'll need a battery in each telephone. Attached is a circuit diagram from Herbert G. White's book 'Telephone Erection and Maintenance' (3/6 net, October 1922). The other end is wired similarly, i.e: L to L; ZE to ZE. Note that the mic is tapped down the battery. 9V may be too much for it, so use three 1.5V cells with a tap off a couple - or simply experiment - the tap may be un-necessary depending on the length of your line.
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Old 11th Jun 2012, 8:11 pm   #9
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Default Re: 1920s Direct line telephone/intercom

Really appreciate this. Thanks all.

I'll try a D cell in each telephone first.
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Old 11th Jun 2012, 9:33 pm   #10
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Default Re: 1920s Direct line telephone/intercom

Given that the original design specifies three cells, you may find that a single cell provides insufficient voltage to drive the bells.
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Old 12th Jun 2012, 6:52 pm   #11
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Default Re: 1920s Direct line telephone/intercom

Actually, I'm mistaken - my Sterling U125s only have three terminals. I'm struggling to find a diagram for these - Bob's site is very good, but only really covers 4 terminal phones of this age (though it does list the U125 and it's GEC equivalent).

I think I posted on here about four years ago when I last had a go at getting them going, but nobody knew then. There seem to be plenty of four terminal intercom phones, but not many three terminal ones. Unhelpfully the terminals are just labelled 1, 2, 3.
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Old 12th Jun 2012, 8:31 pm   #12
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Default Re: 1920s Direct line telephone/intercom

Hi Gents, an exactly similar set, with either 3 or 4 wet Leclanche we used on the local railway siding for the winch operated incline down to the docks until the late 50's.

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Old 12th Jun 2012, 8:45 pm   #13
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Default Re: 1920s Direct line telephone/intercom

I dug my one house phone out last night. Externally it is identical to the ones in the photo, but it is much simpler internally. It doesn't have a coil, and the mic and earpiece are simply connected in series.
It has three terminals, L, BL and BT.
Both bell coils are labelled 2 ohms, and over 2 volts is required to ring it, so 2 or 3 flag or Leclanche cells would seem to be the right supply.
According to the label it was manufactured by the Phoenix Telephone & Electric Works.
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Old 12th Jun 2012, 10:01 pm   #14
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Default Re: 1920s Direct line telephone/intercom

Quote:
Originally Posted by richrussell View Post
I think I posted on here about four years ago when I last had a go at getting them going, but nobody knew then. There seem to be plenty of four terminal intercom phones, but not many three terminal ones. Unhelpfully the terminals are just labelled 1, 2, 3.
Here's a circuit diagram of a Stirling No:U200. It may be similar to your instrument.
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Old 13th Jun 2012, 1:07 am   #15
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Default Re: 1920s Direct line telephone/intercom

Thanks Russell, it's identical, I suppose that was the standard of the day.
1 is L
2 is BL
3 is BT
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Old 13th Jun 2012, 10:47 am   #16
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Default Re: 1920s Direct line telephone/intercom

Many thanks - that does seem to match up with what's inside the boxes.

I'll give it a go tonight - it also confirms my recollection of having a battery at both ends (though not just a single 1.5V cell).
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Old 13th Jun 2012, 11:25 pm   #17
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Default Re: 1920s Direct line telephone/intercom

OK - so the results of my jury rigged setup.

I tried at various times two AND three D cell batteries in each telephone. Battery negative to ZE and battery positive to C.
Line being a connection between both telephones.
ZE was also connected between both telephones.
MC was at times connected directly to battery positive and at times not connected at all.

The push button to ring the bell works - better in one telephone than in the other but I hope that can be resolved mechanically.

I can only VERY faintly hear anything from the earpieces. So faintly I'm not sure it's not just my imagination. There's plenty of voltage so I don't think the problem can be too little power.

Could it be that the mics or earpieces need replacing? Or have I wired it up wrong?

Many thanks.

P.S. Attached a circuit diagram from the telephone's interior.
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Old 14th Jun 2012, 7:41 pm   #18
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Default Re: 1920s Direct line telephone/intercom

I connected up my three terminal Sterling U125s as shown (A1 to B1, A2 to B2, A2 to batt +ve, batt -ve to A3, and B2 to batt -ve, batt +ve to B3) - and they works a treat

Used two 1.5V AA cells at each end, and the other bell rings when an earpiece is lifted and the button pressed. Sound quality is intelligable, if a bit distorted. But it's loud enough.

It might be worth looking at the carbon microphones on yours if it's very quiet - increasing the voltage isn't necessarily the way to get larger amplitude signals with this type of microphone.

Now to give them a dust and a polish, and mount them on the walls. One in the kitchen and one in the sitting room naturally, so I can ring for tea and biscuits
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Old 14th Jun 2012, 7:45 pm   #19
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Default Re: 1920s Direct line telephone/intercom

Hi Gents, sometimes the carbon granules in the mic capsules get compacted, try gentle shaking or tapping.

Ed
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Old 14th Jun 2012, 9:31 pm   #20
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Default Re: 1920s Direct line telephone/intercom

Yes - I will probably start a new thread on that subject. Whilst there is nice loud, audible sound, it's very distorted and sometimes goes quiet.

The first thing to do I think is to go over all the contacts and ends of wire and clean them up to ensure it's not just a poor connection or broken wire. But one phone works better when the microphone is vertical compared to horizontal, which makes me think it's not quite right.

But given these two haven't been in proper use for around 80 years, I'm quite happy so far.
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