Nope, but I have not heard a bad Marshall set to 70% though
. I usually set it by ear and play for a little while to see if I like how it sounds. If I do, I then check to make sure it is within safe operating range. I fried my Fluke meter a few years ago, so I just use a bias rite to 70%. I do not know if the bias rite can handle the voltages that are being put out when is actually playing vs. idle...so I dont risk finding out. I just hit 70% and colse the amp back up.
