Old superheterodyne (T1611E)

Found in a 1949 Radio Electronics, this commercial circuit was found in many countries, including Brazil.

Larger Current CMOS Doubler (CB4634E)
In this circuit, the current capacity doubles, but is still of the order of microamps. The...
Voltage Controlled Oscillator LM3900 (CB19124E)
We found this oscillator in an integrated circuit manual from the 90's. The circuit shows how to...
78xx regulator with logic control (CB21215E)
This regulator can be controlled by a logic signal. The circuit is from an Electronics Now from...