Wall telephone using a Blake transmitter, c 1880s.
© Science Museum / Science & Society Picture Library
The solid back transmitter led to improved transmision and began to replace the Blake transmitter in the 1890s. The early two box telephones, like this one, were converted to three, where the new transmitter arm replaced the middle box. Some of the older two box phones remained in use for local calls. This wall phone was manufactured by the United Telephone Company.