This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
This circuit was published in a 1979 magazine, but it can still be easily assembled as the...
This circuit was found in a documentation of the 80's having characteristics of high overvoltage given by...
Here we show how a Constant Current Source can be created in the Multisim Blue using a common BJT...