The BU10 is clearly a Barretter or current stabiliser but no operating details have been located. The very thin iron wire suggests that this was for stabilising HT rather than heater chains.
With the exposure increased the very clear glass balloon envelope can just be seen.
The fine wire festooned around the supports.
The balloon envelope is 57 mm in diameter and, excluding the B4 base pins, is 116 mm tall.
