PMG telecoms bell, get it working?

1

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? :joy:

IMG_6957
IMG_69573024×4032 1.99 MB

1 Like
2

Hi Jason
Welcome

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.
Cheers Bob

2 Likes
3

Thanks Bob

4

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.

2 Likes
5

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
or
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.

2 Likes