Thanks to Pete Turnbull for allowing me to use this reply that he gave to someone asking about power connectors for his disc drive:
They're AMP (now Tyco Electronics) connectors, though they've been obsolete for a couple of years. You used to be able to get them from Maplin and Farnell, though Farnell don't stock them any more (don't know about Maplin). If the AMP part numbers are any help, here's a file I contributed to one of the sites that lists pinouts (the Beeb power connector is at the bottom):
Classiccmp Friendly Pinout Page
AMP Economy Interconnect 4-way
Used for 3.5-inch floppies and small PC peripherals


NB 2.5mm pitch, not 0.1-inch
Cable connector AMP 171822-4
female contacts AMP 170204-1 (26-30 AWG
) female contacts AMP 170205-1 (20-26 AWG
) Vertical post header AMP 171825-4

AMP Commercial Mate-N-Lok 4-way
Used for 5.25-inch floppies, hard drives, and PC peripherals


Cable connector AMP 1-480424-0
female contacts AMP 163304-2 (18-20 AWG)
female contacts AMP 163306-2 (14-18 AWG)
In-line connector AMP 1-480426-0
male contacts AMP 163305-2 (18-20 AWG)
male contacts AMP 163307-2 (14-18 AWG)
PCB connector AMP 350211-1 (vertical)
AMP 641737-1 (right-angle)
AMP Connector 6-way
Used for Apple and BBC Micro power supplies


Cable/panel connector AMP 1-350241
female contacts AMP 350666-1
In-line connector AMP 1-250234
male pins AMP 350664-1
PCB connector AMP 9-35028

-- Pete Peter Turnbull
Network Manager
University of York