This circuit doubles the frequency of an audio signal, thus changing its timbre. The circuit was found in an Elektor from the 90s. The components are common today.
Below are two frequency filters for receivers using crystals. The crystals must have the frequency of...
We found this circuit in a Radio Electronics from December 1963. The circuit combines valves and...
This circuit published in the November 1964 Radio Electronics magazine powers a light bulb but can...