PRIVATE MANUAL BRANCH EXCHANGES
MULTIPLE AND LAMP SIGNALLING
The main distributing frame is of conventional design, that shown in the illustration below, being of the wall type, and is extensible.
The switch sections, constructed of wood, are of modern design, being free from panelling and cornices, and have iron supports at the rear for mounting, cord, pilot, cord test and operator's circuit apparatus only, thereby ensuring accessibility to the interior equipment.
The dimensions of each section are:-
The jack field is divided into two panels, the multiple being complete over four
panels, i.e., two sections. Strips of 10 jacks and lamps are used for the exchange and
inter-switchboard multiple and strips of 20 for the extension multiple, the lamp strips
being dispersed throughout the respective multiples according to the loading of each
The keyboard is initially equipped with 12 cord circuits, the maximum capacity being
16, each circuit comprising two supervisory lamps, speaking and ringing key, and dialling
and ring-back key. Miscellaneous circuit apparatus, such as hand generator keys, coupling
keys and night service jacks are suitably mounted at the top of the jack field.
MDF and two apparatus racks No. 1 are shown lower right.
Apparatus rack No. 1/35 is provided when a large number of inter-switchboard lines is M.D.F. and Two Apparatus Racks No. 1 required and accommodates up to 35 lines.
Power supply is normally a 24 V. battery floated from a.c. mains by a rectifier, but where
a.c. supply is not available double batteries with suitable charging equipment would be
Line relays for extensions up to 200 ohms line resistance are omitted; over 200 ohms, provision is made on racks No. 1 for the inclusion of P.O. 600 type relays; all other relays are P.O. 3000 type.
Taken from the Ericsson catalogue, edition No. 49
Last revised: September 30, 2019