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This exhibit arrived with flaking zinc metal paint. The Osram logo was present on the paint but no Type designation was visible.
The B7 base indicates a valve from after 1933 and the presence of the top hat top cap puts the date in the mid 1930s.
The construction of this pentode includes a push-fit top mica, side plate anodes and a box suppressor grid. The latter is a bright outer box with wires wound round the box. The screen grid is a close wound and passes across the cathode. The control grid winding is squashed at the supports such that there is just a circular opening that fits close to the cathode.
With extra direct lighting the screen grid is a little easier to see.
The lower screening disc and pinch. The maker's code reads Z8259
The thin glass tube envelope is 44 mm in diameter, and excluding the B7 base pins is 123 mm tall.
Reference: Observation.


Updated December10, 2017.
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