High Power Alarm (CB20475E)

We found this circuit in a Popular Electronics from the 90's. The circuit uses three SCRs to trigger the loads.

General-Purpose Automatic Switch (CB13171E)
The circuit shown in the figure allows a load to be switched on and off (through a relay) at...
Analog Frequency Meter (CB12060E)
We found this simple frequency meter for low frequencies in an English publication from 1978. The...
1 kW power meter (CB9944E)
This circuit has a full scale of 1 kW, being indicated for the 110 V power grid. Adaptations can...