This circuit was found in Ferranti's 1974 transistor manual. The transistors are from the period and the frequencies generated are between 50 Hz and 2 kHz.
In the figure we have the adapter circuit for connecting a headphone to the output of a stereo...
Found in the June 1972 issue of Radio Electronics magazine, this circuit generates signals that...
The output of this circuit must be connected to the input of an audio amplifier. The microphone is a small...