just picked a used one and i think the tubes are bad. I’m getting alot of distortion from the unit even on my clean channel and volume seems to be jumping up or down all over the place. Am i on the right track? the 12ax7wb is the stock tube per the ehx description anybody have suggestions on brand or replacement? Anything I should be aware of when changing the tubes as the instructions were one peice of paper with nothing about replacing the tubes when needed. Thanks for you help.