This circuit was found in an Electronics Now of the 80s applying to NiCad batteries of the time. The circuit is powered by a 12 VAC source, for example, the secondary of a transformer.
This circuit was found in Japanese documentation from the 1960s. It is a commercial circuit with...
This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The...
This simple receiver for listening on the phone was obtained in a 1960 documentation. The circuit is...