Tube location info: The ECC83S replaces the 12AX7. These amps use a split-load phase inverter circuit so no balanced tube is necessary.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 and the GZ34. These are available in the "Related Products” tap as a set of three and will greatly decrease tube rattle.