This diagram was found in the November 1972 issue of Radio Electronics magazine in an article describing benchtop equipment. The transistors are of the time and the frequencies are given by the coils.
This circuit was obtained in the Linear Applications Handbook of the National Semiconductor of...
This circuit is indicated for audio tests, the tracks being selected by the capacitors. The...
This circuit can be implemented with more modern operational amplifiers like the 741 and its...