This traditional configuration found in a Radio Shack document can use 2N2646. More keys can be added, and the power can be supplied with voltages from 9 to 15 V.
This circuit is the factory version of the LM386 low-power amplifier. The sound quality is...
This circuit with transistors of the time was found in the magazine Radio Electroinics of June of...
This circuit charges a battery to power a flashlight at night. The circuit is from an English...