> The highlight was when I was futzing with a slow oscillator and accidentally discovered that using using the speaker transformer as a voltage step up I could get the inductive voltage spike when the relay switched to give a painful shock.

I remember that! In some versions of the manual, this was specifically listed as an experiment, but I think they later removed it.

I just checked, if you go to page 51 (project #43, "High Voltage Generator") of the 160-in-1 manual and you'll find that exact experiment.