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 is basically the same circuit as the previous one, but using PNP transistors. In the original...
This microcontrolled null adjustment for operational amplifiers was obtained in a Linear...
This circuit is from a documentation from the 50's. The transistors are made of germanium. The...