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.

Water-Activated Triac Switch (CB24054E)
This circuit is from a July 1970 Radio Electronics magazine. The sensors are metal probes. The 18 V...
Commercial Radio TR 62 (CB18370E)
This commercial medium and short-wave radio was manufactured in Japan in the 60s. The circuit has...
Variable Timing Ring Counter (CB6107E)
General Electric suggests this circuit in an 80's documentation. The circuit makes use of PUTs...