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.
This circuit is from a Popular Electronics from the 90's. It can be implemented with equivalent...
This two-transistor preamplifier was found in a 1960 Sylvania transistor manual. The output...
The gated oscillator shown here turns on when a “1" Iogic Ievel is applied to the input. The...