You don't need a new bell just a clean out and a new spring. The bell works
simply like a solenoid.
The spring brings the plunger back and it overshoots and hits the dong then
goes back to the middle again.
I had one for years.
As for AC bell transformers, and new bells the answer is it depends. Its
pretty trivial to add a bridge rectifier and convert to DC inside a box
somewhere but you need to know the working voltage and current of the new
ball and if its wrong it might just be cheaper to get a psu for the new one.
I on the other hand used to enjoy repurposing stuff and indeed repairing
bells. There is nothing wrong with those old chimes unless you need a
repeater somewhere else in the property. If you are going to do that then
get a wireless door intercom.
Brian

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The Sofa of Brian Gaff...

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"Muddymike" wrote in message
o.uk...
We have an ancient Freidland door chime which Dongs but no longer Dings:-)
Ive been looking for a replacement but cant work out if I need an AC or DC
bell unit to continue using the current 12v Freidland 764 transformer.

So far Google hasn't been very helpful, do any of you know if this thing
is DC or AC?

Mike