The Balanced ECC81 is located in V6 closest to the power tubes and the standard ECC81 is located in V5. The three High gain ECC83S's are located in V1, V3 and V4.Combo amps are very hard on tubes because of vibrations which can cause tube rattle with any brand of tube. If you play by yourself in a quiet environment or record with your amp you may want to consider using the EuroDamper tube damper rings for the two 6V6S’s. These are available in the "Related Products” tab as a set of four and will greatly decrease tube rattle.