A really useful piece of kit. Can be used as a standard telephone, generate ringing and circuit voltage to test other phones and ringers, or many other uses.
This seems to be a design from the late 1930s that was in production for many years and in use in some small businesses for decades. This is the 1+3 model, i.e. it has just one exchange line and 3 extensions (plus the operator's phone). I bought a pair of these for very little money. My main reason for buying them was that they are of similar age to the Uniselector Clock and I fancied experimenting with the telephone technology of the 1940s to see what else might be achieved.
Specification - http://www.britishtelephones.com/swcb935.htm
The wiring diagram for this exchange is in Post Office diagram N935
Connecting to another switchboard is shown in N785
I've put these links here as UK Cold War related communications were clearly the responsibility of the GPO/BT. I honestly know nothing about this stuff, but do find in interesting.
Vintage Electronics >