This circuit was found in a 1924 Gernsback publication. The variable capacitors are dual. Listening is through a high-impedance phone.
This simple alarm circuit was found in the May 1990 issue of Radio Electronics magazine. The...
With this circuit, obtained from an American publication for radio amateurs in 1976, it is...
This peak indicator for stereo amplifiers uses a CA3130. The 80's circuit does not need a...