[R-390] Black Tube Shields, IERC and cooling fans

[2002tii]

Roy wrote:

>- The military folks had relatively unlimited supplies of spare
>tubes.  Most of us do not.
>- The military had a regular schedule of operational checks and
>maintenance - radio overall performance was checked periodically, as
>were the tubes.
>- For most operational radios, there was a ready maintenance
>capability - folks trained and experienced to make the things work
>right quickly.
>- If a radio quit, there was likely another one to use in its place
>upon patching of the antenna and output.   Not all of us R-39x owners
>are lucky enough to have ready spare radios handy.
>- Some installations (as in aboard many ships) had lots of air
>conditioning running and the spaces were quite cold.

Also, many -- perhaps most -- 390s and 390As were mounted in 
fan-cooled racks with other receivers and equipment.

It is just good practice to keep electronics cool.  The rule of thumb 
is that each 10 degree C rise in operating temperature cuts the 
MTBF50 time of electronic equipment in half.  (MBTF50 is the average 
time it takes for half of all units to fail.)  This is especially 
true of equipment that is already well beyond its MTBF50, like most 
tube boatanchors.

Best regards,

Don