|The Telefunken EVN171 tube
was introduced early in WW-I, and was used extensively by the German
military. It was a triode, intended for use as a low frequency
amplifier. A note that was with the tube when I found it indicated
that it had been removed from a captured German U-Boat at the
Philadelphia Navy Yard. The paper label on the base shows
September 18, 1917 as its date of manufacture.
The internal structure is very unusual. The filament is a length of tungsten wire which droops down close to the grid. The grid is a piece of wire wound into a spiral shape, and the plate is a metal disk just below it. The metal parts are supported by a beautifully made glass arbor. It is a very well made tube and, in that sense, it is very typical of early German tubes. Contrast this tube with the rather crude DeForest CF-185, also from 1917.