This crystal configuration can be made with triggers of any logic. The frequency is given by the formula next to the diagram. This setting is specifically for TTL.
This circuit emits a sound whose frequency depends on the resistance of the circuit under test....
This circuit is from a 1975 documentation, but it can be implemented with more modern transistors like...
This circuit is from an 1977 American publication. The coil consists of 30 + 70 turns of 28 AWG...