Mining and Engine House Telephones
Pattern No. B390, B395, B400 & B405
Comprises Triple Magnet Generator wound to ring through 20,000 ohms resistance, Granular Carbon Transmitter, Double Pole Receiver fitted at end of side arm, Induction Coil and Magneto Bell, all mounted in cast iron case, thoroughly watertight.
A special feature of this pattern instrument is that the arm, to which the receiver is attached, also controls the switching apparatus. When it is required to speak, the switch arm is moved to a horizontal position, thus bringing the speaking circuit into contact, and when released, the ringing circuit is brought into contact.
Pattern 390 - complete with Magneto Bell and extra Receiver
Pattern 395 - as 390 but without the extra receiver
Pattern 400 - as 390 but without magneto bell
Pattern 405 - as 390 but without magneto bell and extra receiver