In the figure we have a stereo decoder from the 70's with pilot lamp for signal indication. The circuit employs a component of the time, which is uncommon today.
The transmitter can be that of CB9574E. This receiver uses a PLL to directly trigger a sensitive relay....
This circuit is from a 1997 publication, but it can be assembled with a BD136 for TR1. The...
Using an operational amplifier with FET, this circuit from a 1977 publication can generate...