Variable regulator with crowbar protection (CB21189E)

This circuit was found in a Popular Electronics from the 90's. The power transistors must be equipped with a heat sink.

Solar Robot (CB25993E)
This is a very simple motor drive circuit with an LDR. The circuit simply powers a small motor. We...
Speed control for electric tools (CB20780E)
This plug-in control was found in General Electric documentation from the 1970s. The SCR can be...
Water Alarm (CB12601E)
This circuit from an old 1978 publication uses germanium transistors but can be implemented with...