Why a variac page?
To those that use them every day, variable autotransformers, usually described by General Radio’s brand name VARIAC, hardly require their own web page. Actually, the variac is a topic that comes up often and repeatedly on the tube-audio-hobby news and discussion groups. As a service to this audience, I’ve put together this humble page in hopes of dealing with some of these common questions. What does a variac look like? Two types are tyically seen; bench models and open frame types. The bench model (typical example to the left) contains the winding in a ventilated metal shield, with the control knob on top. The shield is usually cylindrical, and the variac sits on the bench top like a soda can sits on a counter top. The bench model typically has an on/off switch, a fuse, one or more AC outlets, a line cord and sometimes a current or voltage meter. Open frame types, like the one shown on the right, are intended for panel mounting in equipment racks or as a part of some larger piece of e
