The Balanced ECC83S is located in V5 which is located farthest from the input jack.If you choose to use the KT66's, 6550's or KT88's and your amp has the "Bear Trap" style tube retainers and you don't want to remove or flatten them out then you may want to swap these out for the "Spring and Cap" style retainers. These are 10.00 a quad or set of four and mount using the same screws as the stock retainers. These are also available under the "Related Products" tab as pairs.