BATTERY INTERCOMMUNICATION TELEPHONES
Pattern No. B570
Comprises Hand Combination Transmitter and Receiver, Cord, Bell, Automatic Switch-hook, Relay, Line Selector, and Ringing Key.
5, 10 & 15 line models.
These are cheaper forms of the Secret Service
Instruments, Patterns Nos. B560 and B565, but are in every way reliable and
efficient, and comprise all the advantages of the more expensive instruments.