Found in a 1924 publication, this 2-valve receiver has a speaker output. Power comes from several batteries. Information about the coils is given.
This 16-second voice recording circuit was featured in a telephone answering machine circuit in...
The intensity of an audio signal can be controlled by a remote potentiometer on a DC circuit,...
This circuit was obtained from an old Signalite documentation. Neon lamps are special types of the...