The Balanced ECC83S is located closest to the power tubes in V4.Combo amps are very hard on power tubes because of all the vibrations and these will very often cause tube rattle at certain frequencies. If you have chosen to use the JJ 6L6GC's then we will ship your kit with the special Double Mica 6L6GC’s at no extra charge which will greatly reduce any tube rattle. JJ Electronic started building us a proprietary version of their 6L6GC (the 6L6GC-DM) in 2005 with extra layers of mica. This reinforces the plate structure and all but eliminates tube rattle symptoms. For all other tubes such as EL34’s, KT77's and 6CA7's, we recommend using our EuroDamper rings. These will greatly decrease tube rattle.