I got a Ampeg SVT Classic and recently replaced the power tubes with a new set of EHX 6550's. I replaced the tubes because it would cut off after a while of playing and the standby light would flash red and green. I also could not get the old tubes to bias up to get the green LED's to light up. So after I put the new power tubes in, I still cannot get the green bias LED's to light up. Has anyone ever had this problem? If so what can I do?! Got some gigs coming up and I need the amp working. Any help would be much appreciated!