This 4-tube counter was found in Radio Electronics magazine from December 1959. The circuit uses a coil as a sensor to detect the passage of metallic parts or magnets.
We found this 4W transmitter in a Mullard transistor manual from 1960. The circuit is powered by...
This circuit was found in a 1977 Radio Handbook. The MOSFET supports an equivalent. Capacitor C must...
This simple alarm was found in a 1982 documentation, but uses components that are still common,...