We find this circuit in American documentation from the 1980s. It consists of a frequency folder using a varicap. The capacitors and coils depend on the frequency of operation.
This is one of many possible circuits for the LM3914 IC as an audio indicator. The trim pot has...
This elementary receiver with a crystal earphone was found in Japanese documentation from the...
This circuit was suggested by National Semiconductor in one of its manuals. The LM108 integrated...