After playing around with the little siren circuit here. https://forum.allaboutcircuits.com/threads/siren-schematic.181313/ I noticed that germanium transistors where mentioned. At the bottom of my parts bin I found two OC71 and five OC77. Judging from the leads (straggled with loops) I think I took these out of some old valve radio in my teens. Just out of curiosity, I wonder if they still work? Can anyone suggest a small circuit to test them with? Maybe get these 70 year old transistors to blink a modern day LED or something.