Background

A great deal of confusion surrounds the six pin connectors used by Sinclair Research, Investronica, and Amstrad, on the QL and ZX Spectrum microcomputers.

This is compounded by errors in service manuals, web pages listing the wrong information, and the way the individual connectors in the family are named.

The Connectors

The family of connectors commonly know as "BT phone plugs" or "Type 600" connectors was designed in the late 1970s/early 1980s for British Telecom.

While we are only concerned with the two types of plug and socket used by Sinclair, I feel it is relevant to describe all the connectors in the range (or at least all that I know of) as this helps to explain the numbering of parts.

The various plugs are described in the following table:
Code Description
430A 4-way handset plug (left handed) with A-type polarisation
431A 4-way line plug (right handed) with A-type polarisation
432A 4-way line plug (right handed) with A-type polarisation for S1620 cord
630A 6-way handset plug (left handed) with A-type polarisation
630W 6-way data plug (left handed) with W-type polarisation
631A 6-way line plug (right handed) with A-type polarisation
631W 6-way data plug (right handed) with W-type polarisation

The corresponding sockets:
Code Description
601A through pcb 6-way right handed pcb socket with A-type polarisation
602A through pcb 6-way left handed pcb socket with A-type polarisation
603A right angle 6-way right handed pcb socket with A-type polarisation
605A component side 6-way right handed pcb socket with A-type polarisation
611A right angle 6-way left handed pcb socket with A-type polarisation
612A component side 6-way left handed pcb socket with A-type polarisation

While I have no definitive part number for the "W" polarised sockets, it seems reasonable to assume that their part numbers would be the same but suffixed "W" as with the plugs.

The Sinclair QL service manual erroneously describes the sockets used for joystick and serial ports as "603A LH" and "603A RH"

Right hand vs Left hand

All of the above plugs have a plastic latch on one side and the sockets have a corresponding slot. A left handed plug is a mirror image of the right handed version, including the polarisation keying. The contacts are still numbered in the same order.

The handedness is determined by which side of the plug the latch is on either looking along the cable with the contacts facing upwards or looking from the socket with the contacts facing downwards.

Confusion can arise here when a device uses right angled PCB mount sockets mounted on the top surface of a motherboard etc. (as is the case in the Sinclair machines) meaning that the plug is inserted with the contacts facing downwards, not upwards as is the case in a telephone wall socket. The latching tab of a right handed plug appears therefore to be on the left hand side because the plug is inverted.

A and W type polarisation/keying

The A-type and W-type polarisation refers to the keying grooves found on the back of the connector. These prevent a type-A plug fitting a type-W socket and vice versa.

The keying features of the left handed connectors are a mirror image of the right handed ones.

The Sinclair QL and 128k Spectrum

The QL uses both left and right handed connectors for its joystick and serial ports respectively. The 128k Spectrum uses right handed connectors for both its serial and keypad (later "Aux") ports.

To put it another way: