This 4-tube circuit was found in an American publication from 1947. It is intended for audio distribution lines using a transformer source.
September 2017 - Broadcom's AEAT 8800 Q24 magnetic encoder can be obtained from Mouser...
This circuit uses a 555 (according to the diagram) to generate 50 ms tone bursts at a frequency of 1.5...
We found this mains-powered switch circuit in Electronics Now magazine from July 1994. It could be...