This two-digit circuit was found in the 1999 Radio Experimenter Handbook. It uses the CA3161 and CA3162 A/D converter pair common at the time.
This timebase was found in a European 1980s documentation. The circuit uses well-known components...
This amplifier stage with 1 power transistor was found in the Radio Electronics magazine of...
The basic idea of this 1989 circuit is to trigger a relay for a while when a call signal occurs on...