This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
This circuit uses an audio output transformer found in old transistor radios. Power output is...
This temperature compensated circuit was found in a Popular Electronics of the 1990s. The circuit...
The presented circuit generates a pulse whose delay in relation to the input depends on RC. These...