The purpose of this circuit is to limit the noise of an audio signal. Diodes are made of germanium. The circuit is from an old American manual.
An interesting timer is shown in the figure, using one of the 4 NAND gates of the integrated 4001....
General Electric suggests this circuit in a 1980s documentation. The operational of the time is...
This simple adjustable source uses a PNP transistor that can be the BD136 for even slightly higher...