Hi, this is my first post, I have an old PMG telecoms bell and I’m wondering if I could get it going again with a small battery and an off the shelf doorbell button or am I kidding myself?
I think the exchange batteries were something like 50V and would take up a complete floor of the exchange building with lots of very large 2V cells.
I think from memory the bell arrangement was driven directly by the ring tone which I seem to remember being well north of 100VAC at about 17Hz. could give you quite a bite if you happened to have your fingers on the line when someone rang in.
I don’t think these old phones had a local battery or power supply. Everything came directly from the exchange in a pretty brute force (compared to modern day) manner
So it might not be quite as straightforward as connecting a battery and button. Some ex PMG (as the organisation was known then) people with a good memory might be able to shed some light on exactly how this setup worked.
If you have ever seen an old magneto telephone the rotating handle on the side drives a massive ring generator inside the box. I recall it was an AC voltage of around 100V (60V - 105V) and a frequency of 20Hz. Enough to give you a nip so take care.
So you need to get a “modern” ring generator which looks a bit like a small power supply and I am not sure if you can still buy them. Decades ago they were popular projects in electronic magazines. Note the ringer will not work on 50Hz.
The device you are after is a 20Hz 100V ringer. See, for instance:
Pylon RG-10 400 Type Ringing Generator 20hz 105vac .10A Output Tested 52V Input | eBay
Tele-Q Phone Ring Generator (musson.com)
If you can get the details of those devices you could work out how to build your own. Generating a sine wave that is adjustable from say 20Hz to 60Hz is reasonably straightforward, and an amplifier/transformer could boost it to the required voltage.
Note that 50Hz mains won’t work, and trying to half-wave rectify to get 25Hz probably isn’t worth the effort.
But before doing anything it would be worthwhile checking the continuity of the two coils - if they are open circuit rewinding them would be an interesting(!) job. I suspect replacements would be unobtainable.