This circuit is from an American documentation from 1975. The single junction transistors can be 2N2646 and the signal must be applied to the input of a good amplifier.
This egg timer has been found in an English magazine that no longer exists in 1982. The...
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...
Found in Popular Electronics from the 1980s, this circuit uses two operational amplifiers from...