This circuit, found in a 1977 documentation, indicates when the grid voltage goes through zero. Under these conditions, it produces an output pulse whose duration depends on the capacitor.
The presented circuit is suggested by National Semicondictor in its 1994 Linear Applications...
The circuit shown in the figure generates a rectangular signal whose frequency depends on C1. For...
This circuit is from a Radio Electronics from March 1970. The integrated circuit used is one of...