I am also amazed that you can buy a replacement ZX80 keyboard. This required someone out there to know what it was and to bother to put it on ebay etc. for someone else to find. This is trade at its most obscure, yet this is also our key survival skill - trade. It is what enabled our variation of the human form to survive ice ages where other human varieties perished. We could trade, they could not. Once we traded in things like salt, nowadays it can be in anything including a ZX80 keyboard.
The UHF modulator was replaced in this article, the original modulator was ubiquitous and found in all computers of the era that needed a TV for the monitor. At the time this part was taken for granted, however, it was the component that enabled the home computing revolution, without it and screens would have been an extra £400 or so (as per BBC/Acorn monitor). There must be more information out there on how these UHF modulators came into being.
There's a thriving scene for retro computing in the UK - looks like that is the primary business of the creator. I assume that the (non-test) keyboard, ULA and case all came from a donor machine. After all, there's the link to "Send me something interesting to repair / review / reuse / recycle"
The "expansion" to 16 Kb (and later to a whopping 64 Kb!) was an extremely costly "add on", it was a small "vertical box" attached to the rear end connector (and the connection was - to say the least - flaky):
An image of a ZX81 with the expansion box mounted is here:
But in 1980/1981 kibibytes didn't exist, all we had was good ol' fat Kilobytes made out of 1024 bytes, and WE LIKED IT.
Caveat: I've only ever had them build an unpopulated through-hole board for my one hardware project.
I have an EE degree myself, but soldering has never been terribly enjoyable.
I mean really, you press a key and the screen blanked out as I recall.
Didn't stop me from getting the far superior Vic-20 the following xmas.
More modern TVs have a composite video input which makes the RF modulator redundant. The quality of the picture is much better via composite video.
In fact that is how I used to use my ZX80 back in the day with a wire clipped onto the input to the RF modulator connected to a 9 inch monitor my dad liberated from work!
Tangentially related: The Jupiter Ace was a relative of the ZX81 (same designers, different company) which ran FORTH instead of BASIC. If anyone has one they are worth a lot of money because it seems fairly few were made and/or survived.
I had a 2068.