so i have a kustom HV65. this is my 1st high end amp, well, it may not actually be high end or anything but its my 1st amp that didn't come with a guitar. anyways, i bought her used off ebay. when i play thru the rhythm channel, why does it get all fuzzy and dirty? shouldn't it be clean? also, i was thinking about replacing the preamp tubes 12AX7 with 12AU7. my church lead guitarist told me it would sound better and less overdriven. should i go about doing that? or should i keep the 12AX7? also, i'm considering a speaker changed, the previous owner changed the speaker once to a celestion rocket. i was thinking about the Electro-Harmonix 12VR8, the same church friend told me that it sounds like a broken in vintage 30, just cheaper. anyways, any helpful advice would be great.