Watford Electronics
Co-Pro Adapter
The Co-Pro Adapter by Watford Electronics is an ingenious little contraption for using a Master series internal co-processor board, like the 65C102 "Turbo" board or the 80186 "512" board, externally in any BBC machine with a Tube port.
So you could have a BBC B 512, for instance, or a 4MHz Turbo Model B, or have a Master 128 with a 512 board internally and the 65C102 board externally.
I hope you will click on the picture links above to learn more.