This circuit is from an English documentation from 1969. The circuit can be designed based on modern equivalent transistors. Diodes are general purpose types.
This circuit was published in an English magazine from 1980. The magazine no longer exists, but...
We found this circuit in an old American documentation, from 1971, but the component used is still...
This circuit is from a 1991 publication, but it can be assembled with more modern components. We...