This notch filter was found in National Semiconductor documentation from the 1980s. Operational amplifiers are from that era. The configuration can be adapted to use modern operational amplifiers.
Found in a 1969’s Electronic Design, this circuit operates in a narrow range of voltages....
This power stage with two counterphase transistors and coupling transformers was shown in Radio...
Found in old documentation, this circuit uses special discharge lamps (neon) of the time. The...