I noticed a high pitched constant squeal in my 1974x 18 watt amp and discovered the culprit was my vintage Mullard in V3. It's a shame because the tube sounds fantastic in that position otherwise. The squeal goes away when I turn the TMB channel volume down to about 11 O'Clock, but I like it at about 3 O'Clock for the music I play. The high pitched squeal is most noticeable when I'm not playing and very faint in the background when I am playing. I've just swapped in an old GE 12ax7 and an old RCA 7025 into V3 and the squeal is gone, so I know it's this Mullard. Any hope here or is this tube now trash?