For the past 6 decades Western Electric, Bell Labs and more recently NASA have studied part failures that were brought on by "tin whiskers". These tin whiskers are hair-Like crystal structures that sometimes grow from surfaces coated by mostly pure tin or zinc or cadmium finishes. These are rarely found in audio gear but are more often found in relays, connector pins, IC leads in satellite and miltary electrical gear. Although these whiskers have been studied for years there is still no firm theory as to why they grow and how fast they grow? NASA has had a number of their satellites go down because of this problem. Ok - This is not really Dynaco audio related but it is maybe something you "solder slingers" might find interesting? A 2006 NASA service bulletin about the tin whiskers is at the link below ..
NASA tin whiskers study - 2006
Bob
NASA tin whiskers study - 2006
Bob
