This circuit was obtained in an American publication of 1970, making use of components of the time. Components may be replaced by equivalents.
This circuit was found in English documentation from 1995. The circuit uses a period sensor and...
This circuit for frequencies of 20 to 2 kHz was obtained in English documentation from 1966. The...
This rarity is from a 1926 publication. The galena detector (D) can be replaced in a modern...