Some versions of the 4-125, 250, 400 etc have silver plated pins - certainly
the tubes made by Philips/Mullard and possibly Amperex. Using Goddard's
'Silver Dip' (I believe it's available in the US) as intended for silver
jewellery/trays etc is a good easy way to clean those pins. The
Mullard/Philips variants don't have the metal ring base of the Eimac's -
there are/were Eimac variants without the metal ring base listed as
equivalents, but I don't know about the pin material on those.
Although the silver oxide is supposed to be a conductor, I'm not sure about
the black silver sulphide. The pins appear to run cooler after cleaning, as
far as I can tell with a few minutes testing. Silver Dip works for switches,
too.
73
Peter G3RZP
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