Old superheterodyne (T1611E)

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

Light alarm activating SCR (CB25481E)
This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based...
Timer (CB15603E)
This timer activates a relay after a time interval of up to 15 minutes has elapsed, starting from...
1 kHz tuning fork (CB14363E)
The circuit presented is based on a mechanical tuning fork. The circuit is suggested by National...