This lockable two-position servo control system was found in documentation from the 1990s. The error amplifier can be an operational amplifier and the sensors are phototransistors.
Using the well-known 2N107, one of the first commercial transistors, this circuit produces a 100...
Found in a Hands On Electronics from the 90s, this circuit can be easily assembled today, as the...
This simple MW radio was found in a 1975 publication, but it can be mounted with BC548...