Could have been oxidation on the tube / socket contacts, just like any other connection.
New Tube Owner
Hello, I am a proud owner of a new Music Angel KT88 Amp bought from Ebay... Upon first starting up, there were some distortion coming from the left channel (it wasn't the source, as I changed source and still distortion)... While trying to locate the problem tube, I swapped tubes around then all of sudden, the distortion was gone. What could have happened? Do tubes have distortion until they are burned in? Many thanks...