This circuit synchronized by the power grid can be used as a shield. We found it in an 80's Electronic Engineering. R1 can typically be 4k7.
This configuration appears elsewhere on this site. We obtained it from a 90s Radio Electronics, based...
This circuit is from a Fairchild digital clock module shown in the March 1977 issue of Radio...
This good power amplifier, a few tens of watts, is part of an article in the December 1972 Radio...