This circuit was found in an 80's Electronic Design. It amplifies TTL fast signals for a coaxial cable. TTL is from the S (Schottky) line and transistors are types of the time.
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...