This circuit was found in Mullard's transistor application manual from 1960. More modern transistors can be used. The zener diodes used have the indicated voltages.
This transistor source was found in a 1990 documentation. 2N3055 transistors must be equipped with...
This tube circuit is from an 80's documentation. The filter is of the selective type and the...
This general-purpose two-transistor circuit was found in the November 1993 issue of Electronics Now. The...