12V or 24V heater for RepRap build stage

A heater for the build stage of a RepRap 3D printer which can be made by the standard home etch technique used for making PCBs
This heater has two parallel tracks and can be wired with them in parallel for use on a 12V supply, or wired in series for a 24V supply. The resistance of 1.6 Ohms per track allows quicker heating than the commonly available types..
Two types are provided, the first, HeaterA, was designed for my own printer and has holes for spring supports and locating pins while fo