This circuit comes from a Gernsback Publications of the 90s. The circuit uses a general-purpose transistor as a sensor. The power supply must be symmetrical.
This circuit from a 1970s General Electric publication applies to motors of the series winding type....
This microphone preamplifier with output intensity adjustment is suitable for modulating...
This circuit is from a project published in the March 1996 Electronics Now magazine. The author used...