Dark--I don't that many hours yet on my Twins, but I am quite pleased with them as is. Has anyone dealt with Brooklyn Audio? They quoted me a great price on the MGSi15--However, they do not have the standard model in stock. Evidently, there is an upgraded model with a Pentode/Triode switch, and an external bias adjustment--which costs $100 more. I have never purchased anything from a Canadian dealer--Are there Duty or Custom charges to pay? Thanks!