I am also interested in this subject.  Especially tonal/dynamic differences between 6L6 and 6V6.  There are just some gigs where the 6L6's are just too much - especially with 212's.  And I don't want to add another moving part (power attenuator). 

Thanks!

EL-34's are the way to go IMO

The first thing i noticed about them is that the low end sounded much tighter. Before the low notes were very mushy. Now instead of a big mushy mess on the low E string i get a nice warm twang.

to me the EL34's can put out a wider frequency range but the frequencies are more balanced giving a nice even tone without harshness but still get a nice bright sparkle on the high end. Where as the 6L6 has a narrower freq range but it has more of the highs and lows it can produce, which is why lots of people find them more sparkly (I find it harsh compared to EL34's) but also the lows are more boomy and muddy.


this weekend i got to crank my amp up with the 34's and it sounded perfect. To me with the 6L6's they sound worse as you turn them up because that loose flabby bas becomes much more pronounced and the sponginess of the 6L6 attack becomes too spongy. The EL34's have a snappier and faster attack especially at low volumes, which is why when you crank them up they sound perfect IMO


Just as a side note the EL34's im using are run of the mill Chinese branded sino/shuguang. biased at about 50ma
The 6L6's i tried were JJ's, A set of mesa 6l6GC's and also tungsol 5881's. IMO the EL34's blew them all away with stock bias (around 37ma)

I use 5881's (so does LC). I lioke the sound (not a specialist though)
 Unfortunatly it seems I have fried mine cause I blew my HT fuse.
I do have a pair of Winged C's lying around, but I felt they sounded a bit cold. Might try them again though

I think they may have been mistaken. The power tubes certainly matter. I think the point the poster was trying to make is that you generally want the power section to stay clean (so your clean channel stays clean) Youre not really going to want to get power tube overdrive with this settup due to the two channel settup, which is probably why they said that. where as on something like an old Plexi you need the power tube overdrive to get that signature sound.
That being said each power tube has different characteristics when their clean too (although the differences between the tubes become more pronounced when you overdrive them. ex. 6L6 Looseness)

Not only is it the sound that changes but tubes can also change the "feel" of the amp. And IMO the "feel" and tone of an amp can sometimes change how the player plays, which will (again) change the tone to some degree since 75% of tone is in the fingers

Noob question.
Is the structure of the OTS such that you can interchange just 6L6's with just EL34's at will or is this a decision that is made at the time of building the amplfier?

Eg I can't put EL34's in my Bassman as it is structured to only use 6L6's.

Thanks

They are swappable on both amps with a rebias. This can be done on most amps provided that the plate voltages are high enough for the EL34's but low enough that the 6L6's wont melt.

you'd probably have to swap thetube rectifier for a SS rectifier on the bassman which will bring the voltages up. Weber and a few other copanies sell plug in replacements