Found in an American 1980s documentation, this circuit compares signals from two TTL sources, providing an output that depends on the frequency difference. The circuit can be used as a shield.
This touch sensor, found in an American documentation on transistors, has gained 8 million times...
This power stage with two counterphase transistors and coupling transformers was shown in Radio...
This instrumentation circuit was found in the 1960 transistor application manual. More modern...