Found in an English publication from the 1980s, this circuit can be built with equivalent transistors such as the BC549. The signal must be applied to an external amplifier.
This circuit was found in a 1969 Mullard publication. The transistor may be the modern equivalent...
This circuit uses an operational like to the 741 having been found in a 2001 documentation. The...
Found in English documentation, this timer produces an audio signal at the end of the timing. The...