This circuit generates short pulses. The transistor can be a 2N2222 or BC548 and the frequency is given by the resistors and the capacitor that can be changed.
This stethoscope or hearing aid amplifier has excellent gain. It was found in Popular Electronics from...
We found this circuit in the National Semiconductor's Linear Applications Handbook of 1994. The...
Found in a 1979 documentation, this circuit measures resistances on 5 linear scales. The precision is...