This elaborate mixer is from an Electronics Today International from the 80s. Operational amplifiers are common and resistors with no value determine the gain of the amplification steps.
In this amplifier, the supply voltage is 35 V and the input resistance is 2k2. Equivalent...
This high speed laser diode driver was found in a 1980s documentation. Power FETs can be replaced...
This instrumentation amplifier with differential inputs was found in documentation from the 90s....