Looking for the smoothest richest tone possible from your Mark IV Simulclass amp? This is our Gold Pin Option Retube Kit and it contains four Gold Pin ECC83S's for V1 through V4 and a balanced Gold Pin ECC83S for the phase inverter in V5. Very smooth! The default power tube selection is a matched pair of JJ 6L6GC's and a matched pair of the JJ E34L's in a warmer grade to accommodate the fixed bias power section. With the customize option you can configure this kit to use straight 6L6GC's or 5881's and different EL34 variants for the outside sockets. If your Mark IV is a combo amp then please let us know in the comments section and we will ship your kit with the special Double Mica 6L6GC’s which will greatly reduce any tube rattle.