This simple step of low power audio is from a 1975 documentation. The transistor can be a BC548, and the transformer of the type found in small transistor radios and recorders of the time.
This circuit was published in an English magazine from 1980. The magazine no longer exists, but...
Found in a 1990s Motorola documentation, this high voltage circuit uses a PUT that is not a common...
This proximity sensor was found in a 90s Popular Electronics. The base is a PLL567 that operates...