Quote:
Originally Posted by TonyDuell
I have a field-telephone-like thing labelled 'BR' which I always assumed was from British Rail. It looks like a handset with a couple of buttons (one to energise the speech circuit, the other to apply ringing voltage (battery + buzzer chopper -- the buzzer coil is the speech induction coil too, and you end up with a sizeable voltage on the line, making a loud buzz from the earpiece of the connected telephone). There is no separate ringer/bell in this unit.
I have attached the circuit that I traced out from mine.
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could be the diagram for this one:
https://digitaltmuseum.no/0210262459.../media?slide=0
dsk