Hey, I recently switched the tubes in my VH4 from Electro Harmonix EL34s (they were in the amp when I bought it) to SED 6L6s, and the differences are subtle, but noticable. I definitely like channels 1 and 2 much more with the 6L6s, it seems like 6L6s suit them better (a bit more "blue" sounding- sorry, I tend to think of sound in terms of colours, not sure if this makes sense), though I liked channels 3 and 4 better with EL34s thanks to the extra crunch they added. Depends what you're looking for and which channels you use the most. I mainly use channels 1 and 3, and of the two setups right now I'd rather have 6L6s because of the way channel 1 sounds. However, if all you use on this amp are channels 3 and 4, go for the EL34s (just stay away from chinese tubes) and see what you think! Hope this helps. Cheers!