[R-390] Black tube shields

[2002tii]

Barry wrote:

>Black Tube Shields - How about having the shiny tube shields coated with
>Black Oxide at a metal heat treat facility.  I have steel coated with Black
>Oxide frequently - it will also add a degree of corrosion protection.

Black tube shields aren't just fashion accessories -- IERC (and 
similar) tube shields lower both plate and envelope temperatures 
significantly, but not just because they are black. They have 
internal contact fingers that conduct heat from the tube envelope to 
the shield body, and they grip the shield base very tightly to 
conduct heat to the chassis.  Silver tube shields actually raise 
plate and glass temperatures compared to leaving the tubes 
bare.  Blackened, they may be marginally better than shiny, but the 
tubes would still run significantly hotter than bare tubes.

Also, shiny tube shields are generally plated -- to add a black oxide 
finish, you'd have to strip the plating off first.  Adding a coating 
over the plating (paint, powdercoat, teflon gun finish, etc.) would 
only increase the insulating properties and further raise tube temperatures.

Best regards,

Don