This circuit for frequencies of 20 to 2 kHz was obtained in English documentation from 1966. The transistor can be any general purpose and powered by batteries.
This headphone amplifier using a pickup coil can be used as an extension for devices such as TVs,...
This circuit uses common components activating a control relay for the water pumps. The sensors are...
We found this circuit in a 1967 El3ectronics World. The transistors are from the era but can be...