[Collins] Service Bulletin 303?

[Gerald Johnson]

http://www.amwindow.org/tech/htm/r390man.htm
discusses the conclusions of the bulletin. That same discussion shows up one other place according to my recent google search.

IERC shields lengthen tube life, shiny nickle plated shields shorten tube life. No shields is a better codition than the shiny shields unless the radio is being used mobile in rough terrain where the vibration and shock might eject the tubes from their sockets.

IERC shields make the tube envelopes run cooler and so probably keep the pin seals sealed better. The shiny shields reflect heat back to the tube and make the envelope run hotter which stresses the metal to glass seals more and probably makes them leak more rapidly.

73, Jerry, K0CQ, Technical Advisor to the CRA