[Amps] Paint it black

[Ken Brown]

> Working this in the reverse, I replaced a transformer in a 32V2, where the 
> rectifier as I recall is directly adjacent the (black) power transformer. 
> The transformer got very warm during operation. I put a thin Al sheet in 
> between the transformer and the tube and the transformer was notably 
> cooler  (Tubes being cheaper than transformers to replace).
>   
Only worked because the tube is at a higher temperature than the 
transformer. The separating plate stopped the direct radiation from the 
tube to the transformer, reflected some of the heat back in the 
direction of the tube, absorbed some of it and reradiated it over a 
larger area, and maybe lost some small amount of the heat due to 
convection. Due to the reflected heat and the portion re-radiated back 
to the tube, the tube no doubt ran hotter than before. As you say, 
easier to replace the tube when it fails sooner due to running at a 
higher temperature, than to replace the transformer. So you accomplished 
something worthwhile.

In the case of two tubes dissipating nearly identical amounts of power, 
and running at nearly identical temperatures, there would be very little 
advantage to having the plate between them, as far as stopping radiant 
heat from one tube to the other. The heat from tube A stopped from 
getting to tube B by the plate, would be offset by tube B's own heat 
being reflected back to tube B. The net advantage, as far as radiant 
heat transfer goes, would be zero, so it would not matter whether it is 
black or shiny aluminum.

The control of the air flow might be useful. The color only effects how 
the absorption and radiation works.

DE N6KB