Found in an 1868 Mullard documentation this circuit has a dynamic range of 10 Hz to 25,000 Hz. Modern equivalent transistors can be used.
This circuit goes into operation producing a sound on a small speaker when the supply voltage...
In the figure we have two simple configurations of voltage doublers. Resistors and diodes are...
This timer was found in an English publication from 1979. The circuit can be powered with voltages...