This circuit generates the busy tone of ordinary telephones. The transistors can be the BC548 and the components of the T filter and the multivibrator can be changed to obtain the exact tone.
Found in a publication from the 50's, this circuit uses a germanium transistor of the time. The...
This circuit was found in an English publication from1979. The circuit can be assembled with a...
The circuit shown in the figure uses general purpose NPN transistors and can be used to generate...