Who is recommended for doing repair work on B-15 heads? The tubes in my B-15 have a slight red hue on the plates which makes me think they are drawing too much current. I would adjust the bias current myself but I do not know how this is done on a B-15 (mine's 1972 era). I'm assuming this involves changing a resistor. The main reason I ask is i'm considering replacing the no-name chinese tubes in my amp with some NOS Sylvania 6L6GC or 7581A/STR387 and believe I will need to rebias the tubes. I emailed Jess Oliver but have not heard a reply back. I could take the amp to a local guitar store (the techs there apparently are reputable) but I really don't want to spend hundreds of dollars to change a resistor.