I have been asked to help repairing 2 ringers for a railroad system, but I have never seen such ringers before. They have 2 coils of 3000 ohms each (in series). The mechanical design is pretty equal to the typical ringers on Antwerp telephones. The coils of the ringers are broken, probably due to lightning.
They run this 18 miles (30km) line on bare wire and insulators, an have as much as 15 phones on the line.
I have been able to locate coils that fits, but they have only 1400 ohms each, so how will a 2800 ohms ringer be as a replacement of a 6000 ohms ringer. I may ad a pair paralleled diodes in opposite direction placed in series with the ringer, this will stop the leak of voice signals, but else???
Her is the ringer with new coils. Resistance 2800 ohms, impedance approx 8860 ohms at 25Hz (Including series diodes) It rings from 25V and up (Not tested with more than 70V, but usually these are working well at 90V too)
The railway party lines used the high Z (impedance) ringers to allow the mentioned number of phones on a single line.
The ringers do not only have a high resistance but are also very sensitive, together with powerful magnetos it is made sure that in fact all phones will ring simultaneously on this safety system. Is it for an active (museum) railway? They'd still need approved communication devices.
What type of phone is it? Disused railway phones are out there as parts donors. You could even swap the ringers, the lower Z ones will work fine in a less critical hobby/collector application.
The other possibility is to find an electromechanical shop that is able to rewind the coils properly. That might be hard these days...
If safety and originality are non issues, you might investigate into electronic ringer circuits.
Yes it is an active railway, I do not know much more.
Might be this railway, as it's 18 km long :)
Good luck with the repair! Has it been tried to just use the lower Z coils? Chances are it works as well... in real life there would be mobiles to back up the antique system in a pinch. But the technical surveillance authority must be involved of course.
Here is some info about the railroad (in norwegian): https://njk.no/kroderbanen
(https://njk.no/kroderbanen)and a map: https://njk.no/praktiske-opplysninger/kart-over-banen
Now I have been able to measure 2 OK high ohm ringers, REN load = 1/3 or an ipedance of 21300 ohms, and the one with lower ohms coils was only 8860 ohms so this will be a difference.