can i ask about repairs on this board?
looking for some ideas on what could be causing this horrid sound coming from my randall rg100es guitar amp head. when i turn the master past 4 the amp starts howling. not the high pitched positive feedback sound but a low midrangybassy hollow 'howl" that drives the speaker crazy. the speaker starts to vibrate real hard like its gonna blow up. i all i have plugged in is a guitar. kinda lost on this one

thanks for any responses.