The proper tube shields can easily identified.  They are anodized black (or deep purple), have an open top with a series of tabs folded over a thin, octagonal metal tube inserted longways inside the shield.  They are also plainly labeled "IERC."  There is a unique model number stamped on the outside of the shield denoting which size it is designed to fit.  Refer to this number when obtaining the shields.

Below is an inventory with individual quantities of the 5 different part number IERC tube shields used in the R390A:

      (1)     6025-B   Tall 9 Pin, used for the ballast tube
      (9)     6020-B   Medium 9 pin, used on 5814A's and 26Z5W's
      (2)     5015-B   Short 7 pin, used on the 5654's
    (13)     5020-B   Medium 7 pin, used on 6BA6's, 6C4, 6AK5, etc...
      (1)     5025-B   Tall 7 pin, used on the OA2

Black tube shields labeled "WPM" my also be found.  While I personally don't feel these are quite as effective as the IERC design, they are far and away better than the shiny types described below.

Radios which still have shiny, nickel-plated tube shields should have them replaced with the above IERC shields as soon as possible.  Even if they have been painted black on the outside, these shields have no provision to grip the tube bottle and sink the heat away from it.  Also, the bright internal surfaces of the shield actually reflect the heat back into tube and on to its dark internal plate structure which could then cause the tube to over dissipate and shorten its service life.

Page prepared by R. Charles Rippel

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URL: http://www.R390A.com
Revision: 03 March 18, 2001
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