This electronic rheostat with SCR was found in the June 1964 Radio Electronics magazine. The SCR may be a modern type and the 2W potentiometer may be 470 ohms.
This circuit consists of a small inverter that can generate a few hundred volts of DC voltage...
The use of a detector bridge instead of a single diode, as is normally done in common galena...
The LM150, 250 and 350 series of 3 A are manufactured by several semiconductor industries that...