KEY AND LAMP UNIT No. 4
Key and Lamp Unit No. 4/6A
A flat panel comprising strip of 6 lamps and provision for mounting up to 6 "1000-type" keys. For use with PMBX No. 3/3A to provide Priority Signalling on inter-switchboard circuits

Key and Lamp Unit No. 4/12A
A flat panel comprising strip of 12 lamps and provision for mounting up to 12 "1000 type" keys. For use with PMBX No. 3/5A to provide Priority Signalling on inter-switchboard circuits.

Introduced circa 1963.

Drawings - 91957 & 92043 (No. 4/6A) and 91958 & 92047 (No. 4/12A).
BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems
Last revised: August 11, 2025
FM