One thing that has been enjoyable for me as I research different amplifier heads each week is learning what tube or valve options are out there. Some amplifiers have 6L6 tubes, some have EL34 tubes and some have the KT66 tubes. What does someone like me (with limited understanding of the tube types) do with this information?  Perhaps someone like me needs to get themselves an amplifier head like the THD Univalve that lets you switch the tubes quickly and easily without a need to re-bias the amp. Cool right? … 52 Amplifier Heads, week 14—THD Univalve