Nebulous did this some time ago and posted some samples. Maybe search for his thread or PM him for his opinions.
Anyway, here are the samples he posted:
http://dl.getdropbox.com/u/437070/Nebulous JSX Tube Comparison.rar (32MB File)
Lol, thanks for posting that Hack. Saves me looking for it.
I really need to get onto some more clips when this album is finished in the coming weeks.
Ok, first up, I can like the El's and the 6L6's equally, depending on the day haha.
The EL's have a mid/ high mid voicing that is great in the room, but abit much under a mic. They are also a touch more grainy in the topend both in the room and under a mic.
The 6L6s are a touch scooped in that region, which is good for the JSX as it allows you more control over the general mid region.
Hoestly though, I would recommend spending your money on some smoother preamp tubes and some bias probes. I think the hotter bias on either of the tubes sounds better than what we get from factory.
A point to note about the JJ tubes: I put a full set (pre and power) into the JSX and the power amp tubes went bad after a year, so I put the old ones back in.
I will be trying another brand for the power amp next. I may go back to JJ one day, but I did find it odd that they gave me grief so quickly and I would like to see if I can get abit more agression in the mids.
Hope that helps.
