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 consists of a switched mixer with digital touch control. The circuit was found in old...
This low noise, low frequency instrumentation circuit was found in a 1976 NASA circuit manual. The...
This is a circuit suggested by Linear Technology in a 1980s documentation. The integrated circuit is from...