This circuit was found in documentation from the 1970s. However, it can be implemented with modern transistors such as 2N2222 for Q1 and BF494 for Q2. The crystal depends on the desired frequency.
We found this circuit in the National Semiconductor Audio Handbook of 1977. The circuit produces...
Found in American documentation from 1968 this circuit is based on discrete components in addition...
This circuit used in instrumentation is suggested by National Semiconductor, now Texas Instruments and...