I've not been following this discussion in detail, but to me the issue seems
pretty straightforward. A black shield around tubes will radiate heat away
from the tubes, since the black absorbs radiation (hence the reason it looks
black). That's why the most desirable tube shields in vacuum tube radios are
the black IERC shields, for which collectors pay a premium price. On the
other hand, a shiny metal shield will reflect the radiation back to the tube
(which is why it looks shiny), so the tube envelope will run hotter.
I see no benefit at all to using a black shield as a partition between
parallel transmitting tubes. Each side of the shield will absorb the same
amount of radiation from its adjacent tube, so the shield will have no
temperature difference across it. With no temperature difference, there
will be no heat flow. Hence the shield neither helps nor hurts, insofar as
tube cooling is concerned (unless the shield is bonded to an external
heatsink which can conduct away the absorbed heat). The result will be the
same whether the shield is black, shiny, pink, or whatever.
73,
Jim W8ZR
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