I don't post here much, but I happened to notice a thread from a short while back about cleaning up tube pins. Good idea, but someone suggested using Tarn-X.
As an ex-Fab-rat at Motorola, Intel, and Hitachi, I know a few things about cleaning metals. Tarn-X is designed for cleaning precious metals...platinum, gold, silver and the like (and also is OK to use on copper). BUT, this stuff contains sulfuric acid (H2S04), and will be bad news on the pins of vacuum tubes (usually nickel-steel). It will start a chemical reaction in the metal of the pins that will be difficult to halt (and inserting the tube in the socket can potentially transfer some of the sulfuric to the female side of the pins, adding insult to injury). I can just see a nice quad of vintage EL34 Mullards getting ruined by this stuff. Urg...
Indeed, I've fixed a lot of connection problems by cleaning pins, but I use the old-fashioned Brasso and a Q-Tip. Does a great job and will do absolutely no harm to the metal pins (Brasso is basically ammonia, IPA, some fine polishing talc [silica?], and a tiny bit of oxalic acid). I much prefer this method over any other since it is not only safe, it removes none of the metal of the pin, or at least so little you'd need an SEM to measure it. Since many sockets are already sloppy, the last thing one really wants to do is to reduce the diameter of the pins any further with something like sandpaper or even a Scotchbrite pad (or eat the metal away with sulfuric). A good polishing with Brasso does the job and is actually easier.
Rock on, gentlemen.