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Old 1st Feb 2011, 3:37 pm   #1
slderiron
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Default Magneto telephone setup

I bought the pictured pair of Ericsson N2121Z magneto phones, along with a set of bells and a further magneto at auction, with the intention of connecting them and getting use out of them. When I crank the magneto to the boxed bells, they ring, though it appears there are parts missing from the bell box. The phones seem in good order, though one of them had quite a bit of coal dust in it. I'm not sure why the seperate bell-box and magneto came with the phones, as the phones already contain their own bells.

My question is; can these phones be connected and used? I really have no idea how to go about it. I understand I have to connect an external power source to provide 2 or 3 volts? I think I ought to test the phones as well, just to make sure they actually work, before attempting to connect them together. Any ideas would be gratefully received, regards, john.
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Old 1st Feb 2011, 4:00 pm   #2
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Default Re: Magneto telephone setup

I have one of these wired up to my 'house circuit': the 1212 in the sitting-room and two type 'F' field-telephones in office and shed respectively; it works a treat!

I used a spare core in the house telephone circuit for one connection, and earth for the other, with the shed-to-house link doubling as a long-wire receive aerial when needed.

The 1212 works fine with a 3V battery (2 x 1.5V 'C'-cells connected to the appropriate terminals on the N1212).

You won't need the extension bell and separate magneto; they were probably to enable other, non-magneto instruments to be used on the system. Being mining telephones, I'm guessing they will be intrinsically safe and may have a reduced voltage from the magneto (I had a pair of mining type 'J's like that) so they will work with each other, but may not ring a field-telephone bell, if connected.

Connect all your extensions across one pair of wires (your line wires from the telephone) and connect a 3V or 4.5V battery to the appropriate terminals on each telephone. You'll need a system of rings to work as a party line. If you haven't got a circuit diagram for the N1212 I'll put one up on the forum when I get home.
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Old 1st Feb 2011, 5:29 pm   #3
AlanBeckett
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Default Re: Magneto telephone setup

The reason one bell has coal dust in it is that they were (Surface) pit phones - Picture 2.
No, they weren't IS by modern Standards, but were used extensively underground via a Barrier. Right through to the '90s they were still on Cert Drawings showing them in the same cables as real IS Telephones. Unfortunately I never got to play with them.
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Old 1st Feb 2011, 7:03 pm   #4
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Default Re: Magneto telephone setup

Quote:
Originally Posted by AlanBeckett View Post
No, they weren't IS by modern Standards, but were used extensively underground via a Barrier.
Ah... I happened to notice the extraordinarily large bell-bobbins and the stonking big magnet (compared with my model - actually a 4109B, but similar to the N1212) and wondered if it were to do with a): working from reduced magneto voltage, or b): being electrically damped - although on a.c. with no trembler I wouldn't have thought this would make any odds.

I attach a pic of my magneto desk telephone. It may be similar to yours (there are several variations!), but you should get some idea as to how to connect the battery and the line.
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Old 1st Feb 2011, 9:00 pm   #5
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Default Re: Magneto telephone setup

Thanks for the info. I think I've already got the diagram showing the layout, but unfortunately I'm not technically minded enough to read it and translate it into putting the wires in the correct places. What I'm hoping is for anyone on this website who has the time to painstakingly point out where each wire needs to go; where to connect the 3 volts (where the positive and neg terminals connect into the phone) and where on the terminal board (3rd picture I think) I connect the wires into each phone so as to connect them together (or do I connect the phones via the cables coming from the back of the phones).
We're dealing with a novice here, but I have had success getting a bakelite phone's on/off switch and neon indicator light working again, and that was with the help of a chap by the name of Andy (I think), from this website, so I'm confident I can get these phones working again with a little perseverence. Regards, John.
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Old 1st Feb 2011, 10:46 pm   #6
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Default Re: Magneto telephone setup

I think we'll start with getting both telephones to work as a pair, without any extra magnetos or bell-boxes. Could you put up a photograph of the circuit-diagram of one of the telephones so as to be advised? It'll be stuck inside the instrument somewhere.
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Old 1st Feb 2011, 11:52 pm   #7
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Default Re: Magneto telephone setup

Many thanks, attached.
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Old 2nd Feb 2011, 12:19 am   #8
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Default Re: Magneto telephone setup

Assuming (always dangerous!) all is well elsewhere, then connect your instruments as follows:-

1): On each instrument, connect a 3V or 4.5V battery, positive to terminal 10, negative to terminal 9. Leave the link in place between terms 1 and 10. You should hear side-tone when blowing into the mic at this stage, even with the telephones unconnected. Polarity isn't important, as the batteries are local batteries and are just to excite the microphones.

2): Connect each telephone together by taking terminals 10 and 3 in one telephone to terminals 10 and 3 in the other telephone. You should now be able to crank the magneto on one instrument and the other should ring.

Try this and report back. Given the amount of coal-dust in there, you may need to clean the contacts on the back of each magneto (they should pull in when cranking and drop back when the crank is released).
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Old 2nd Feb 2011, 5:49 pm   #9
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Default Re: Magneto telephone setup

Well these phones seem to be largely working! One of the phones' bells doesn't ring as shrilly as the other phone although it is quite loud enough to discern an incoming call, and the same phone is a bit on the quiet side on the receiver. There is quite a bit of crackling. The other phone works perfectly well in all respects. I was considering connecting a 4 1/2 volt supply to the underperforming phone sometime this evening as I have currently connected 3 volts to each phone. However given that one phone works perfectly well on 3 volts I feel this probably won't make any appreciable difference.

There's a wax cap in each of the phones, maybe one of these is leaky. Of course there is also some coal dust in one of the phones, could do with a clean. The problem might also be in the handset. I was considering swopping over the handsets, and if the problem moves over to the other phone then the issue is with the handset.

Incidently I didn't connect directly to the board in the phone, but to the cable coming out the back of each phone. They're already connect to the connections you specified. Best regards, john.
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Old 2nd Feb 2011, 6:48 pm   #10
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Default Re: Magneto telephone setup

The carbon inset mic in my Ericsson always benefits from a little shake of the handset before use. Maybe worth drying them out, as discussed elsewhere on here. Stick them on the radiator for a day and see if there's an improvement.

As for the connections - even handier!
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Old 2nd Feb 2011, 9:13 pm   #11
slderiron
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Default Re: Magneto telephone setup

I tested them again this evening, after extending the cable further so that the phones are as far apart as I can get them. I found that the longer the phones were spoken into (after about 1min) the better the connection became, until there was no difference between them. There is still the odd crackle but nothing serious. I think its probably due to the old wax capacitor, but I'd rather keep them in as they're the original parts.
Also, the bells are ok on both the phones. When I got my brother to crank the bells earlier, I was unaware that he didn't give a good hard crank. It wasn't until my son got back from school, that I was able to test them for a bit longer and I realised they were both fine.

What would have been the purpose of the seperate bell-box and magneto? They seem surplus to requirements.

Can you advise the best type of bakelite polish, both phones are very dull and could do with a good clean to get them back to the way they looked in 1950. Regards, John.
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Old 2nd Feb 2011, 9:42 pm   #12
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Default Re: Magneto telephone setup

Quote:
Originally Posted by slderiron View Post

What would have been the purpose of the seperate bell-box and magneto? They seem surplus to requirements.
I'm guessing that they would have enabled another non-magneto telephone to work on the system, or perhaps allowed signalling from another room?
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Old 2nd Feb 2011, 10:12 pm   #13
slderiron
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Default Re: Magneto telephone setup

Aye perhaps, it makes sense that extra bells would have been used as it was probably quite noisy at the coal pit. If I wanted to link this bell set to the phones could you advise which way to go about it? I posted a pic of the bell set with its diagram. I might not be able to do this though as the diagram shows that there was an induction coil and condenser as well as several terminals, all of which are missing.
Many thanks for your help in getting these phones working.
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Old 3rd Feb 2011, 12:14 am   #14
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Default Re: Magneto telephone setup

The first thing you'd need to do is to ensure that you have the correct terminals to the bell in the box (it's a bellset No:1 with the gizzards pulled out - making it a bell). You should be able to find the leads out of the bobbins which, with any luck, will be connected together in series such that applying a magneto voltage to the other two terminals will ring the bell. Use your handy magneto telephones to test! Once you've done this, I would lead the bell-bobbin wires to an internal connector block to take the strain of any additional wiring.

OK, then - you now have a working bell...

What you now need to do is determine which N2121 telephone you wish to connect this extension bell to and wire it by removing the link between terminals 1 and 10 and connecting your extension bell in their place. The extension bell will be in series with the N2121 bell which, I note, is a 2000 Ohm version - used for long lines. I suspect your extension bell will be 1000 Ohms, but will still work.
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Old 3rd Feb 2011, 4:46 pm   #15
slderiron
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Default Re: Magneto telephone setup

Ok, I'm much obliged for your help on this, I look forward to setting this up. Best regards, John.
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