It's hard to build an oscillator

Two things not mentioned - hey maybe I should blog about these myself and post them up?

The first being the "Two Transistor Metronome" that I can't even remember where I saw first - possibly Electronics Today International or Hobby Electronics, although Practical Electronics was a contender - we didn't get that one much though. I remember my dad and I building this when I was probably about seven or eight, and I've built loads since.

https://tinyurl.com/22qjecj7

It's a relaxation oscillator where the two transistors form more-or-less an SCR, which fires when its (negative-going) gate voltage exceeds its anode voltage. Kind of.

A similar circuit using three transistors and a diode is used in the oscillators in the Roland TB303 and Korg MS10/20/50 series, with a current source used to set the capacitor charging time so you get a nice linear sawtooth. Conveniently the expo converter turns an incoming control voltage into an exponentially-rising current, which is just what you need!

I was thinking Astable Multivibrators. Probably the same as your Metronome. The circuit I usually see uses two NPN transistors instead of the PNP+NPN your metronome does: https://www.electronics-tutorials.ws/waveforms/astable.html

It's a different principle, although I have a Ladybird Book of Electronics that my dad gave me when I was just about the age my son is now, that shows how to make a thing that flashes two lightbulbs using that astable circuit (and a few other things).

The two-transistor metronome one really is working more like an SCR, that rapidly charges the capacitor and allows it to discharge again.