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 simple photometer circuit uses an LDR as a sensor and the indicator is a sensitive...
This circuit generates sinusoidal signals between 300 and 3000 Hz. We find a 303 Circuits from the 90's....
This oscillator uses germanium transistor avaialble in 1958 when the project was published....