This circuit was found in the March 1997 Electronics Now magazine. It uses a common analog indicator and the transistor is a general purpose one.
We found this amplifier for hearing aids or hearing aid using only transistors in a documentation from the...
Found in an English publication from 1977, this circuit uses only 1 LED. Unlit means heads and lit...
We found this circuit in an old documentation. The indicated solenoid is of low current type,...