My HT-5 has recently been acting weird. The volume is beginning to flutter a bit, and it is sounding a tad muddier by the day. I'm thinking it probably needs new tubes. The amp was manufactured in 2009, and I think it is running the original ECC83 and 12BH7 tubes. I've heard some tubes lower the gain, some increase the gain, some give the clean channel more headroom, etc.. This will be my first experience with this process, and I wish to get tubes that will get me as close to metal as this particular amp can get. Anyway, I'm open to suggestions other than "get a new amp".