We found this circuit in a Hands-On Electronics from the 90s. The circuit must be connected to an external amplifier. Frequency control is capacitive, using an antenna for this purpose
This is the commercial circuit for the TRF-44 amplifier sold in Japan in the 1960s. The circuit...
This circuit uses a common cathode display and TTL integrated circuits. We found it in a 2001...
This circuit was found in a 1992 publication, using an operational amplifier not very common...