Using the 2N2646 this circuit was found in a Radio Electronics magazine from July 1968. The transistors are from the time and the lamp can be replaced by a high-power LED in a current version.
This circuit is originally recommended as hearing aid or stethoscope. The output transducer is a...
Originally suggested by Popular Electronics to control Christmas lights, this circuit can...
The purpose of this circuit is to detect output signals from a transmitter for the frequency range...