Active audio filter (CB21770E)

This circuit was found in a 1977 documentation for radio amateurs. Integrated circuits are common operational amplifiers.

M 204 Ibrape preamp (CB15082E)
In the 70s, Ibrape launched an excellent audio pre-amplifier kit to be used in amplifiers of the...
Impedance Adapter (CB18282E)
This amplifier stage was found in a 1956 Sylvania manual and has an unusual configuration with a...
1200 W power supply for 144 MHz transceiver (CB7429E)
Found in a QST magazine from the 90s, this powerful unit is intended to supply a VHF transceiver for...