The ECC81's are located in V4 and V5 in the back row. The Balanced ECC83S is located in V6 in the back row farthest away from the input jack.Combo amps are very hard on tubes because of vibrations which can cause tube rattle with any brand of tube. If your amp is the combo version and 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 power tubes. These are available in the "Related Products” tab as a set of four. These will greatly decrease tube rattle.