Vertical Variable Autotransformer

Radiotone Single Layer Roller Contact Vertical Variable Autotransformer (colloquially known as Variac) construction looks like a conventional 3 phase transformer as can be seen from the picture.

Speciality of this Variable Autotransformer lies in winding Cu strip of appropriate cross section edgewise. This reduces the length of the column to 1/4 as compared to winding widthwise, thus making it compact. This column is then polished & roller carbons are made to make contact with winding for current collection. Due to circular column construction, a Double Carbon assembly can be provided giving two outputs 180 degrees out of phase (or as it is known + and - type).