The GPO (General Post Office) / PO (Post Office) Tester No. 275A is a portable functional tester designed for Signalling Units used in PCM (Pulse Code Modulation) systems.
This specialized equipment was used by GPO/British Telecom engineers in telephone exchanges for testing and maintenance, specifically looking at how PCM signalling units functioned, often in conjunction with equipment like the
PCM Signalling Unit 1A or similar digital transmission hardware.
- Purpose: It functions as a functional tester for PCM Signalling Units, ensuring they properly send and receive signalling data over PCM transmission paths (e.g., junctions between exchanges).
- Portable Design: As noted in the GPO Test Equipment manuals, this was a handheld or portable unit (a Mark 4 is pictured in some documentation, with the Mark 2 being an earlier, similar variant).
- System Type: It is specifically designed to test the signalling units associated with early GPO PCM telephone transmission systems.
- Tester Series: It belongs to the 200-series GPO testers used for voice, signaling, and line testing, likely often used with 24-channel PCM systems common in the 1970s/80s.