I'm attempting my first bias on my EL34 Shiva. I purchased a dual bias tester, $20 DMM and a pair of SED winged "C" EL34's. I put the new tubes in, let them get real hot and the closest I can get them adjusting the bias pot is within 5mv of each other. One tube measures 30mv and the other 35mv. Is this much mismatch acceptable or should I tell the guy I bought the tubes from they're not a matched set?