This circuit is from a Ferranti publication of 1968. The circuit generates a signal according to the crystal. The transistor may be a modern equivalent.
This circuit is from 1977 documentation, but can be assembled with BC548 for Q1, Q2 and Q4, BC558...
Found in American documentation from the 90s, this circuit uses components that are still common...
This high impedance input amplifier is suitable for the use with piezoelectric sources such as...