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 oscillator, from an old Argentine publication from 1973, uses the inductance of the 500 ohms...
Found in Popular Elecronics, this configuration also appears in this section, but obtained from other...
The operational ones used in this project are old types from National Semiconductor, since the...