Did my O level on one in 1986 & by 87 had a second one with 64K of ram (Slogger Master Ram board) which replaced the CPU with a daughter board, a faster CPU & 32K of shadow ram.
That machine had a 3 way toggle switch added which provided 3 modes:
* Normal - where it ran as a standard electron
* Turbo - where the new cpu ran at top speed (can't remember the speed off hand)
* 64k - where the video remained on the original ram but the OS ran on the shadow ram - so BBC Basic had more ram available than the BBC B had.
Then there were the floppy drive (+3) added to it.
Ah takes me back.