Also known as a variable autotransformer. This type of dimmer
is now virtually obsolete. It consists of a single winding autotransformer and a carbon brush on a rotating shaft. This allows dimming the input voltage
while maintaining the sine wave
of the line
. These devices are bulky and heavy, and not suited to remote control except via cumbersome fixed-speed motor drives.
A common variant of autotransformer, the Variac
, also allows boosting the input line voltage to about 140V by placing the input tap on the transformer
between the maximum end-of-travel of the carbon brush and the 0V neutral
tap. This type of device was used on the 1975 Broadway production of A Chorus Line
to boost the voltage to the 1000W FEL lamps in the Strong Trouperette
III followspots, to gain
(Luxtrol) and Ward-Leonard were the primary manufacturers of autotransformer dimmers for the theatre
The model shown below, a Luxtrol "six pack," contains six 10A dimmers, which could be either electrically mastered by a 60A dimmer, OR the 10A dimmers and the 60A could be independent from one another.
The model below contains six dimmers of 10A-60A capacity. The handle on the far right (without a breaker
), is a mechanical master. The Tee Handles are rotated 90° horizontal to lock into the master, or vertical to be independent. The oval plastic Tee handles identify this unit
as one manufactured by Altman
, using Superior Electric Luxtrol autotransformers. Complete units manufactured by Superior Electric had tubular plastic handles.
Director & Designer Series: MICHAEL BOLL- Cleveland Lighting Designer