I just broke out an modern amp that had not been turned on for many months. the amp uses a quad of el84's and I had a nice set of NOS Mullards in there (thanks Mike/KCA many moons ago). While playing I did notice that the amp did not have the clean headroom that I always recalled it had in the past, but I thought nothing of it. When I was done playing I noticed that only 1 of the power tubes had a cloudy getter flashing -vaccume has been compromised. My questions, BEFORE I put another NOS Mullard in there are, 1. Could playing with only 3 of 4 power tubes working done any harm to my amp? 2. Is the fact that only 1 tube blew mean anything? 3. Is this soemthing that I should have a amp tech look at? Thanks.