The Balanced High Gain ECC83S is located in V4 farthest from the input jack.If your amp is the Combo version you may want to consider using the EuroDamper tube damper rings for the two power tubes. Combo amps are very hard on tubes because of vibrations which can cause tube rattle with any brand of tube. These are available in the "Related Products” tab as a set of four and will greatly decrease tube rattle.