I ordered some more boards from this shop: they look the same as the one I described in my previous log entries. Spare "D882" transistors and TL431 chips are also at hand.

Now I need to figure out how to decouple the feedback path from ground in a way that's easy to do and that doesn't look to kludgy. I ordered small diamond cutting discs which might be the right tool for this job. Let's see what works best.

Edit: as of October 2020 boards are still available from the same shop above. If you're looking for alternative sources look for a blue board with a single push button, not two.