This circuit was obtained from Dutch documentation from 1967. It uses transistors of the time which can be the BFY50 and 51 for the output and the BC series for the others.
In the figure we have the simple way to obtain an integrator with an operational amplifier of type...
Found in 1980s documentation, this circuit uses a small transistor radio output transformer and a double...
Found in a 1969 EEE, this circuit is based on an operational amplifier of the time and on old type...