This circuit for a digital module was found in the September 1989 Radio Electronics magazine. The source must be symmetrical to the operational amplifier.
This circuit is from 1995 documentation. The power depends on the transformer, which in this case...
This 1967 Electronics World circuit is suitable for frequencies up to 1 MHz. The setting applies...
We found this circuit in a 1983 English magazine, but it can be easily assembled with the BC548...