Good Day, I just picked up an Ampeg PF-50T and ordered their PF-112HLF cab which should be arriving tomorrow. I've read through all the product material referencing tube biasing. I'm wondering, how does one know when to bias the tubes? Ampeg's owner's manual indicates this is to be done when changing tubes and also as they age. I understand the reason for biasing new tubes but how should one rebias the tubes as they age? What are the signs to look for and sounds to pay attention to? The literature also indicates that for the best tone but shorter tube life one should "under bias" the tubes. On the PF-50T this would occur just before the red light comes on. Is their any tonally perceptible difference in doing this? Best Regards, -Greg P P.S. I'm super excited to get this amp up and running. It's the perfect small venue/recording amp i've been waiting for someone to make.