This converter for WWV time reference station signals was found at Popular Electronics. The 15 MHz signals are now received on a medium wave radio at 1 MHz.
This SCR circuit can operate on frequencies from 1 to 20 kHz. We found it in an American...
Here is a very useful circuit that can be expanded, including the use of more integrated circuits...
The same basic audio oscillator as the CIR15855E can be modulated automatically by a relaxation...