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.
The operational amplifier used in this application is uncommon today. This Raytheon circuit can be...
This conventional bistable power control circuit using triac was found in the June 1970 Radio...
This short-range experimental transmitter emits a signal with many harmonics, without modulation. It can...