This circuit was found in a 80s American documentation. The zener diodes determine the points of action of each stage and the transistors can be general purpose types.
This experimental circuit was found in a technical publication from 1976. The diode can be of...
Using the LM3909 this circuit was found in the January 1992 issue of Radio Electronics magazine....
This circuit can shift the phase of a signal from 0 to 360º. FETs admit equivalents and the...