[PickleRick63]

Originally Posted by TonyDuell

Is the electrical part of the bell just the coil, or are there interrupter contacts as you would find on a DC bell?

Thank you Tony - that makes sense: this must be a DC bell. I can see interrupter contacts on the arm of the bell (having read up on a Wikipedia page about electric bells!)

Originally Posted by Dave Moll

Regarding the bell, your descriction sounds like a DC trembler bell. Have you tried feeding it with a DC voltage between 6V and 12V independently of the rest of the circuitry?

That's a good idea Dave. I am certain this is a DC bell now.

Looking at your third image, I cannot see the wiring clearly. The blue wire of the bell appears to be connected (via the 5th terminal of the telephone) to the green(?) wire of the black cable that I take to be the line cord

That's correct

and the yellow wire of the bell is connected to the yellow of the line cord (I assume the component at the bottom is just a connector block).

Also correct

If this is correct, how is the other end of the line cord wired?

Green and Red go to the master socket via pin 2 and 5, and yellow to pin 3 (on a BT plug)

Also, to what, if anything, is the black wire of the line cord connected?

It is not connected at either end.

So my options are to work out how to make the DC bell work, or to exchange it for an AC bell.

To make the existing one work I'd be looking at using an additional power supply and some kind of relay. Or perhaps by using a voltage rectifier to convert the AC supply to DC - is this feasible?