Hello all! I'm having trouble EQ'ing my peavey 6505+, the main problem I have with it is the presence control. When the presence control is on 1-9 the amp sounds muddy/dark but when I put it on 10 the amp is too bright. I see a lot of my favorite bands playing this head and their presence control isn't near 10 and their tone sounds amazing! I got this head used a year ago and the guy said he changed the tubes about a year before that. He swapped out the stock ruby tubes for JJ preamp tubes and two different sets of GT power tubes (which I thought was kind of strange). So the tubes are about 1-2 years old. My setup is fairly simple I go from my Ibanez 7 string with emg's into a tc electronic tuner into a Maxon and then a boss NS-2 set up in an x connection between the fx loop and front of the amp. Then the peavey 6505+ goes into an orange 2x12 cab. I usually only run the heads volume knob on 1 or 2 at home and on 4 for gigs. I use all monster cables with the exception of the speaker cable and patch cables for the pedals So what do you guys think the EQ issue is? Could I have bad tubes, could the head be biased wrong, or is it because I run the amp at a low volume, or could it be something else? Much thanks everyone!