I only recently learned the term "tube rolling"... I've recently purchase a 2 channel custom 20. I'm looking for a more compressed, more Marshall type of tone. (Please don't tell me to buy a Marshall I've owned and tried many but they have their downsides). I'm hoping that changing, if possible, the 5581's in the 2-channel 20 to EL34 which I'm guessing greatly contributes to that more Marshall type of tone? I like the 2-channel custom for it's feature set, the fact that it comes in a head (otherwise I might have bought an Archon), it's wattage, weight, etc. 1) is this possible? 2) what is the level of effort e.g. any modifications required Can anyone point me in the right direction? Links, etc. Thanks.