This Vox circuit uses a specific Motorola component. We found the circuit in the 1990 Linear Databook of the same company. The transistor must be in accordance with the switched load.
This electronic Morse Key for telegraph message transmission was found in an American 1980s...
This PWM control circuit was found in an old documentation, but appears elsewhere on this site...
Found in a 90s Radio Electronics, this circuit uses an AD590 or AD592 for remote temperature...