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The 253 is a directly heated battery pentode. So far we have found no information on this brand or this valve Type.
It is a true pentode with three wire grids. At the top are two filament tension springs.
The oval anode seen side on. The support for the tension springs is held in both mica sheets.
The grid wire is just visible above the lower mica.
The suppressor grid follows the anode shape whereas the inner grids pass flat across the filament wires. The filament can be seen to be pulled into the V slot in the top mica and thus the path through the grids is clearly defined.
Another view of the top of the envelope.
The wide glass tube envelope is 28 mm in diameter, and excluding the IO base pins is 85 mm tall.
Reference: Observation.


Updated March 09, 2019.
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