Mastertone M-12 Tube

Mastertone was one of the hundreds of small, independent tube manufacturers that flourished briefly during the 1920's.  This company, like many others, was located in Newark, NJ.  Shown here is their type M-12, which was equivalent to the RCA WD-12.  It was probably made around 1925.

The WD-11 and WD-12 tubes were electrically the same, but they used different bases, with different diameters (the WD-12 was larger).  To save production costs, some tube companies used bulbs appropriate for the smaller WD-11, and used oversize Bakelite bases for the WD-12 equivalents to compensate.  The Mastertone was one such tube.

What truly sets it apart, though, is the cobalt blue glass bulb, the colorful decal, and the evacuation tip at the top.  It is, without a doubt, one of the prettiest tubes ever made.