This circuit was obtained from HAM Radio magazine in an 80's issue. The FETs are types of the time and the frequency is determined by the crystal. The circuit operates at voltages from 3 to 9 V.
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...