Hi, I'm guessing that your i/c is longer than 3m. That would be the reason it would not have adjustments. If so, there would be a shrink-marker on the dowmstream end saying HIGH, MEDIUM, or LOW. If you let me know, I can tell how optimum a match this might be to your amp. The question of whether Magnum is good match for Tube amp concerns the SPEAKER CABLE, not the interconnect.
ATB,
Joe
ATB,
Joe