The 65-in-1 kit was one of my treasured childhood experiences (circa 1974). I ended up with a degree in electrical engineering, though I was probably on that path anyway.

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 wrote down that wiring diagram so I wouldn't lose it. One of my brothers had built a 9V variable power supply in a high school shop class, so we made use of that to create a pain game: hold the two leads and turn up the 9V supply output until you gave up. Whoever got the voltage knob the highest won. Our arm muscles would be involuntarily twitching, like a TENS unit.

The other game was one person would hide it in the house somewhere, say a closet, and the other person would use an AM radio to locate it, as the spike would release broadband RF energy which could be picked up by the radio. The closer one was the louder the clicking would come out of the speaker.