Advance Transformer 71a6091 Autotransformer Ballast

The Advance Transformer 71A6091 CW autotransformer ballast is a metal-halide ballast designed for a 400W ANSI M59 lamp. It uses a constant-wattage autotransformer (CW) topology and is compatible with 120/277V AC supply. The 71A6091 designation sits in the 400W M59 ballast family (MH BAL 400W M59) and is referenced alongside other 71A60x models in Philips/Signify’s Advance ballast catalogs, indicating interchangeability within the same specification family. This ballast supports a 400W metal-halide lamp and is intended for luminaires that require the CW autotransformer approach to regulate current and maintain light output across the applicable input voltage range. When sourcing a replacement, verify that the fixture’s ballast footprint, lamp type (M59), and electrical input (120/277V) match the 71A6091’s specifications to ensure compatibility and safe operation.