I just bought some 6L6 tubes to replace the EL34's in my JSX. Not familiar with biasing a tube amp ... are there hard and fast rules or do i need to bust out a multimeter to make the adjustment? Not sure if it's a switch (liek a mesa) or a POT I need to adjust. Tech's in my area want to hold the amp for over a week! It's like a 15 minute job to boot! I've some guys on another forum that basically are like pop them in and be done with them ... but that sounds plain wrong. Will ballparking the adjustment give me horrid results? I wish there was a local guy that could do this while I wait.