Heintz & Kaufman Type 5 Gridless Triode

Manufacturing tubes in the early days was complicated by an interlocking set of patents which made it impossible to legally produce a useful tube without paying royalties.  In an attempt to circumvent the DeForest grid patent, Heintz & Kaufman Ltd. of San Francisco developed a line of gridless tubes which they called "Gammatrons".

The pictured tube is the smallest of this line and was intended for receiving use (the other Gammatrons were transmitting types).  This is the type "5" from about 1930.  Internally, there are two plates with the filament between them.  The filament is significantly closer to one plate; presumably that is the control element.  The base is aluminum, with a ceramic insert. 

It is quite safe to assume that this approach did not work well.  This tube never went beyond the prototype stage, and this example is one of only 3 known to exist today.

This tube was a gift from the late Howard Schrader, noted pioneer tube collector.