The selected circuit was found in GE's 1977 semiconductor manual. 3N84 is a controlled silicon switch and SCRs support equivalents. The transistor can be a BC558, depending on the supply voltage.
Based on Maxim documentation, this circuit can control a motor using a MAX295 class D audio...
This circuit was found in an Electronics Now from the 90s. The frequency depends on the crystal. The...
This simple experimental circuit, with a good external antenna can capture distant stations in the...