This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
In the figure we have the way to make the three-phase control of a motor using opto-diacs. The circuit is...
We find this simple musical instrument in a 1977 Radio Shack documentation. The key resistors must be...
This circuit was found in General Electric documentation from 1966. The circuit is suitable for any...