Sad news to hear today that Sir Clive Sinclair has died. The man created the ZX80, ZX81 and ZX Spectrum(s) personal computers which were very popular in the UK and which a great deal of people learned to code with. A huge loss to the world but what a great legacy he has left !
Clive SInclair did a lot more than the ZX81 - not all of it very good but often very innovative if not very reliable:
I remember:
The X10 - a switching audio amplifier round about 1965 - never owned one: sinclairX10
The Z30 and Z50 amplifiers https://oldwww.nvg.ntnu.no/sinclair/audio/z30.htm
The IC10 - a horrible IC power amplifier that mostly didn't work (mine never made any sound at all 
)
The calculators: https://oldwww.nvg.ntnu.no/sinclair/calculators/cambridge.htm
The Black Watch (did you never wonder where Apple got the idea ) https://oldwww.nvg.ntnu.no/sinclair/calculators/cambridge.htm
The C5 - not that much less practical than current electric cars https://oldwww.nvg.ntnu.no/sinclair/vehicles/c5.htm
There's a nice website for all things Sinclair https://oldwww.nvg.ntnu.no/sinclair/contents.htm
MK
Clive SInclair did a lot more than the ZX81 - not all of it very good but often very innovative if not very reliable:
I remember:
The X10 - a switching audio amplifier round about 1965 - never owned one: sinclairX10
The Z30 and Z50 amplifiers https://oldwww.nvg.ntnu.no/sinclair/audio/z30.htm
The IC10 - a horrible IC power amplifier that mostly didn't work (mine never made any sound at all )
The calculators: https://oldwww.nvg.ntnu.no/sinclair/calculators/cambridge.htm
The Black Watch (did you never wonder where Apple got the idea ) https://oldwww.nvg.ntnu.no/sinclair/calculators/cambridge.htm
The C5 - not that much less practical than current electric cars https://oldwww.nvg.ntnu.no/sinclair/vehicles/c5.htm
There's a nice website for all things Sinclair https://oldwww.nvg.ntnu.no/sinclair/contents.htm
MK
... The X10 - a switching audio amplifier round about 1965 - never owned one: sinclairX10...
"add your own choice of tone control circuit." 
