The original was plated brass and used on very early wireless sets, along with "Watch, Non-Magnetic, W/T" (which was actually cheaper than the standard pocket watch and had an iron instead of brass case). It ended up with with a stores code when they got around to numbering stuff, but was replaced by the bakelite version (which kept the same designation & code), presumably when they realised they would need them in large quantities and it was quicker and cheaper to use plastic.
Chris.
|