This receiver was found in a Japanese publication in 1967. The circuit uses germanium transistors and details of the coils are not given. Power is supplied by a 9 V battery.
Using an operational amplifier, the figure shows how to convert the waveform to low frequency...
This high quality circuit with complementary symmetry was found in an Electronics World of 1966....
This circuit was obtained in an old 1983 magazine, but it can still be easily assembled. The...