The difference between this circuit and the previous one is that it uses PNP transistors. The circuit is from Radio Electronics magazine from July 1968. The frequency depends on R1 and C1.
This article was obtained in a French magazine Nouvelle Electronique from 1994. It can be easily...
Suggested by Sprague in the 1980s documentation, this circuit can control three-phase AC motors....
Figure 1 shows a low-pass filter using a 741 operational amplifier but other ICs can be used. The...