[R-390] Tube Cooling

[2002tii]

The original research was published in a Technical Report by the Rome 
Air Development Center, "Extending Electron Tube Life with Tube 
Shields" (A. Coppola, 1958).

Also see MIL-DTL-24251 (2008) and its predecessor, MIL-S-24251.

Some data points:

A bare tube will run cooler than the same tube with ANY non-contact 
tube shield (silver, black, open top, cutaway, whatever).  So, if you 
do nothing else, remove all non-contact tube shields except the very 
few where electromagnetic shielding is important.  Older 390/390A 
manuals give explicit instructions in this regard.

Contact-type tube shields (e.g., IERC) reduce tube temperature 
dramatically below the bare-tube temperature, and increase tube 
life.  NOTE that these tube shields depend on conduction to sink the 
heat removed from the tube, so they need to be used with tube sockets 
that have collars at least 1/2" tall.  If there is no 1/2" collar, do 
NOT use a contact-type tube shield.

Best regards,

Don


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