This is probably the earliest project for which I have a physical record. I was in high-school, and had enrolled in an electronics class. I was quite disappointed when it was announced that our project for the term would be the construction of a "digital clock" kit (premade circuit boards etc.), as I had already home-built such a device (*note). When I mentioned this to the instructor, he asked what I would like to build, and the first thing that came to my mind was "I've always wanted an oscilloscope.".
The following week, everyone arrived at class to find a tidy little kit of components, displays and a circuit board for a digital clock - except for me - at my station was a 3KP1 display tube, with a photocopy of the schematic from an Eico service manual wrapped around it.
Regretably I no longer have the machine, and the only photo I have is this artical which was published in the local paper. Inside are several twin-triode tubes mounted on the chassis, connected by point-to-point wiring. Power is supplied by a transformer scavanged from a television set with a 600v secondary winding for which I constructed a diode/capacitor voltage tripler to obtain the high-voltage for the display tube. The metal enclosure was generously custom built for me by the schools metalworking shop.
The result worked remarkably well, and was more precice and linear in operation that I think any of us really expected. I used this machine as a primary bench tool throughout the remainder of my student years. Later, after I had acquired a commercial scope, I advertised the machine on a local BBS and sold it.
(*note: Thankfully I don't have a photo of my digital clock which was constructed a few years earlier - it consisted of digital components glued upside down inside a wooden box, will all connections wired point to point between the exposed IC pins. The displays were tiny "MAN-7" board mount displays which had suspended in an opening in the front of the box by the solid wires used to connect to them. It worked - but some things are truly best forgotten!)