I put the jj el34l's in my roadkingII with the jj6l6's. To me the el34l's definitely have more low end than a regular el34. I decided to compare the el34l's directly with the 6l6's. Since the roadking has progressive linkage, i put it on one pair of 6l6's and played then i put it on the pair of el34l's and played. Same channel, same settings, same guitar. The 6l6's have more highs and have more low end. The el34ls have more mids, upper mids, lower mids. The 6l6's are tighter, el34l's are crunchier. For my main high gain rhythm i stick with 2x 6l6's, for my clean i use the 2 x 6l6's. I use the el34l's for my lead tone. I've tried mixing one pair of 6l6 and the el34l's but it takes away some low end and tightness as well. WHen i use all the power tubes 2x 6l6 and 1x el34l still doesnt have the tightness or low end of just running the 6l6's. Just my two cents.