Recently I recieved a new Budda amp that was damaged in shipping. Budda sent me a replacment amp while I kept the damaged one. In the meantime...I was able to get the damaged one working well enough to gig with it until the new one arrived by replacing the broken Electro Harmonix 5U4 rectifier tube with a Groove Tubes 5U4. When the replacment amp came, with a EH 5U4 installed, out of curiosity I tried both 5U4 rec tubes in the new amp. To my surpise..the GT sounded noticably better. It gave a more detailed sound and a bit crisper. It surprised me by how much difference there was. I managed to break my GT tube last night and called a "very reputable vintage dealer" for a replacment. The dealer, somewhat rudely I thought, told me I must be hearing things as there is no way that a tube rectifier can effect your tone because no signal passes through it. Other than making me feel like a fool....it got me wondering if anyone else has experienced hearing differences in brands of rectifier tubes. I know that theoretically there isnt supposed to be a difference...but I SWORE I heard a difference between the GT and the EH 5U4.