I've made these before but they're fun. My objective is to eventually make a direct conversion receiver for 40m that is small enough to fit inside an Altoids tin, including the 9V battery. As you can see, I'm a long way from that objective:
This is the classic NE602 LM386 design from EMRFD except that I'm using a permeability tuned oscillator. I'm hunting for long brass machine screws (and the nuts to fit, probably about 3cm long and 3mm diameter. (If anyone can suggest a source I'd be most grateful). A steel screw works but quenches the oscillator as I screw it in. (Is that why brass is used?).
The other issue in miniaturisation is getting small components - some of my capacitors are huge, due to voltage rating, and I need to collect smaller ones.