Pattern No. B250
Comprises Granular Carbon Transmitter, Watch Receiver, Cord, Automatic Switch-hook, Induction Coil, Bell (fitted on backboard), and Push Button.
Patterns Nos. B250 and B255
These Battery Wall Sets are cheaper forms of instruments than B245, but are in every way well made, useful, and efficient. Pattern No. B250 has the Transmitter fitted inside the case with Projecting Mouthpiece, and Pattern No. B255 has the Transmitter fitted outside the case.