This QST circuit generates 4 frequency signals according to the crystals used. Transistors admit equivalents although the indicated types can still be found with some ease.
This circuit was obtained in a 1991 Electronics Handbook. The publication no longer exists, but...
This crystal radio version using a detector diode was found in documentation from the 90s. The...
This circuit, from a documentation from the 1970s, produces two sinusoidal signals given by C2 and...