|my personal BD-72||Wiring diagrams||TM11-330 excerpts||Hacked BD-71|
BD-71 / BD-72 Wiring Diagram
|Switchboard BD-71/72 are 6 line and 12 line minimal modernizations of the WWI EE-2 switchboard.
BD-71/72's offered improvements such as an operators set made from EE-8 components.
A buzzer was substituted for the normal ringer.
Fixtures to hold batteries for the buzzer, lights to see the drops and for the operator's microphone were also included.
A thumb screw terminal block for easy line installation was added in the rear of the unit.
This terminal block also included arc/spark gap surge protection.
This removed the need for the fuses found on WWI EE-2 switchboard/drop/line units.
The void left by the fuses was used for 3 position switches to connect to the operators set and ring generator.
Information from http://www.royalsignals.org.uk Document # 670
(EE-2, The Monochord Switchboard, USSC Electrical Eng. Pamphlet No 2, 30/6/1918)