This step of good gain was obtained in an American publication of the 1980s. The circuit can be powered by voltages from 3 to 9 V and the FET can be of almost any type.
This 3 and-a-half digit circuit was found in a Teledyne documentation from the 90s. The circuit uses...
Found in a 1990s Popular Electronics, this circuit produces a tone on a small speaker. The keyer...
This series sensor circuit is from 1995 Popular Electronics. The circuit can use any SCR and the...