I think it's just a high power potentiometer. The "smoothing" may refer to being able to adjust 300V from 0V to 300V "smoothly." Harold --=20 FCC Rules Updated Daily at http://www.hallikainen.com Not sent from an iPhone. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .