Last week I went to see a customer of mine who bought a Consonance M99 tube amplifier. As I went, I took along some tubes I new would be fine in his amp bus also my tube tester Amplitrex AT1000 and some cleaning stuff like Deoxit.
When I arrived at his home, it was very hot but quickly I started Testing all his tubes wich where 6L6 tubes from Reflector and NOS Philips ECF82 (which I never have seen before). They all measured OK. After testing we put on his amplifier and listened to some music.
After about a half of an hour I heard some noise (crackling) from the left channel but also I noticed the left channel playing less loud than the right channnel. After some testing I decided to do some testing at home, where as I know, my loudspeakers are fine.