This Schmitt trigger was found in old documentation. The transistors can be of the general-purpose type like BC548 or even 2N2222.
Found in na 1970 EDN this circuit has a parallel regulation providing a symmetrical output of 15 V....
This circuit is from an American documentation from the 50's. The transistor is the CK721, and the...
The figure shows how to use an operational circuit as a voltage divider. The circuit is from a...