SOURCES

Information about vintage telecommunications equipment is widespread on the internet.

The website of Fons Vandenberghen covers all aspects of telegraphy: https://telegraphy.eu/index.html. 

A good starting point for telephony is https://www.britishtelephones.com/. On European phones there is www.matilo.eu.

A vast amount of information about old radios is found here: https://www.radiomuseum.org/