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This exhibit has the etched marking of 4 in a circle but is a 1920s R Type bright emitter derivative.
The filament is a single strand and the electrodes are co-axial within the cylindrical anode. The grid diameter is smaller than the R Type.
The strap across the grid adds extra rigidity.
Just below the anode the filament voltage is etched and reads 4V-0.7A.
The electrodes seen close-up. The tungsten filament is held in place by being crimped to its support. The $ of the identification is on the left.
The filament is still intact.
The balloon envelope is 56 mm in diameter, and excluding the B4 base pins is 81 mm tall.
References: exhibit.

 

Pin Connections
B4
1
2
3
4
a
g1
f
f

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
4.0V
0.7
Updated October 02, 2011.
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