This QST circuit generates 4 frequency signals according to the crystals used. Transistors admit equivalents although the indicated types can still be found with some ease.
The circuit shown below is from the National Semiconductor's 1994 Linear Applications Handbook. The...
This metronome was found in a 1979 publication, but it can be assembled more easily with the BC548...
This circuit for a maximum current of 1 A is the most common version that uses the 78 and 7905...