Cursed circuits #6: reverse avalanche oscillator

Last year, I published an article titled “It’s hard to build an oscillator”:The title alluded to the fact that there’s no shortage of oscillator circuits on the internet, but many of them use unusual parts, need weird supply voltages, or don’t work well (if at all).But sometimes, bad rises to an art form. Here’s probably the most puzzling bad oscillator you can assemble today with the parts you have at hand:Reverse avalanche oscillator. Other small NPN transistors should also work.At first blush, nothing here makes sense. The transistor is upside down and its base terminal is not connected. And yet, the circuit works: hook it to a supply of about 14-20 V and watch the LED blink.If you connect an oscilloscope to the terminals of the capacitor, you’ll see that the cap is repeatedly charging to about 10 V, then rapidly dumping some of the charge, all the way down to 9.1 V:Capacitor charge state with a 14 V supply (5.8 Hz oscillation). By author.It’s no mystery that the capacitor must be…