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.
This preamplifier appears elsewhere in this section and this version was found in American...
This 2000 circuit, found in the documentation of the time, is intended for charging this type of...
Based on the well-known LM3909, this LED pulser circuit was found in American documentation from...