I recent did a switch in my 1979 Marshall 2203 JMP amp which was a US model one with 6550s and had it modded to take el34s which I just bought the JJ E34L tubes here as well and I am happy with there sound as well. I play a lot of AC/DC so hence why I switched to El34s. I ordered one Mullard CV4004 12ax7 along with the power tubes to try something new. I currently have the mullard in V1 and it sounds great. I know a lot of sites say this tube is the highest gain 12ax7 you can get right now but that is far from true. This tube is an average gain tube which I think most people want but the thing I loved about it compared to a few others I tried in V1 was the tube is clear and warm with a bit of that fat cream to it. It didn't sound as brittle or harsh compared to a few other GT and JJs I have tried in V1 and it still packs a great punch. I would buy this tube again for sure!