This 1 MHz oscillator was found in an Electronics World of 1969. The circuit uses a general-purpose FET and the output circuit must be resonant at the generated frequency.
The transistor can be the BD135 and this circuit, found in a 1978 publication, can be powered by...
This second-order filter was found in a 1978 publication and can use common operational amplifiers like...
This circuit has a sensitivity of 2uW. We found it in documentation from the 1980s. The integrated...