That is a pretty preamp! What tubes does it use? I just glanced at Rogue's site and couldn't tell. My guess is that two of those tubes are for the phono preamp, so rolling them won't do any good unless you are using them (if you are listening to vinyl, rolling the phono preamp tubes will probably make a bigger difference than rolling the line stage tubes)! The other two tubes are probably the line level preamp. It would be typical if they are dual triodes where one tube is for each channel, and one triode of each tube provides gain and the other is the mu follower, which lowers the output impedance. Rolling won't matter much at all to the mu follower, as it is essentially a 100% feedback devices, and feedbacks very nature is to eliminate any distortion, and thus whatever sonic characteristics the part has. But, the other half of those tubes (if I am right about the topology) is the gain stage, and rolling it will make a difference (though the magnitude of that difference will depend on how much feedback is applied.) You can't swap half a tube, so you'll of course replace the whole thing.
So, the moral of the story is, ask Rogue which tubes do what (or see below). If you have four 12AX7's, you can't really guess without looking at the circuit or asking. If you have two 12AX7's and two 12AU7's (or some other lower gain tube), I'd bet that the X7's are the phono stage and the U7's are the line stage. So, figure out which tubes are providing the gain in the line stage, and swap those. When you know specifically what you are looking for, folks here and elsewhere will have all sorts of opinions about which particular type sounds best.
I just typed all that and realized that you could just pull tubes to figure out which ones do what. Don't pull them all at once, and don't run it for too long without a pair, as the voltages will likely be a little high due to the reduced load on the power transformer. But, pull tubes two at a time. When you've found two that you can pull and get no sound from either channel, those are the two to roll. You can, of course, plug something in to the phono stage and confirm the results, as pulling the other two should mean the line stage works but the phono input is silent.
that was ramble-y.
Paul
