Used with a Sender No.
9A, 9B and 9B-1 on public exchange switchboards and PMBX No. 1A / PMBX
No. 11 switchboards.
Use
Key-Unit No. 4/1A - Used in public exchange switchboards and PMBX No. 1A &
11 switchboards.
Key-Unit No. 4/2A - Used in public exchanges on DQ operator switchboard
positions.
Key-Unit No. 4/3A - Used in public exchanges on International operator
switchboard positions.