This circuit was obtained in a Popular Electronics of the 90s. The circuit uses integrated from the time, uncommon today. Note that the speaker has a higher impedance than ordinary speakers.
Published in an old Popular Electronics, this circuit makes use of components that are still...
Suggested for the control of photographic enlargers, this 1967 General Electric circuit uses still...
Found in old documentation, this oscillator operates with high voltage. The diode must be of the...