Want all the gain you can get from your Mark IV? This is our High gain Option Retube Kit and it contains four Handpicked High Gain ECC83S's for V1 thru V4 and a balanced ECC83S for the phase inverter in V5. Rippin gain! The default power tubes are a matched quad of the JJ 6L6GC’s but you can configure this kit to use the JJ 5881’s by clicking on the "Customize" button! Either can be used in the Simulclass and Non-Simulclass amps. If your amp is the combo version and you choose to go with the 6L6GC's 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.