This is not much of a big project but it was a thing I did so I will include it. I found this old JCM 315 Spectra on Craigslist for $20. It was so cheap because it was not functioning and was unreliable. But I picked it up figuring that I could at the very least use the 15 inch speaker.
I took it apart and messed around a bit and got it back up and running. It sounds pretty good and is pretty loud for how small it is. And then, of course, the speaker blew on me. So what I was assuming would be its only value ended up being its only flaw.