Hey Playa, first off I'd just like to say that I'm not very familar with the XXX, and also that anyone with enough time and money can make something work if they have too, having said that let's take a look at your situation, First off the swap to EL 84's would probaly be more expensive than you would be willing to pay, the EL 84's have a 9 pin base, 6L6's have a 8 pin base, so the tube sockets would have to be replaced and rewired to accomadate EL 84's, which leads to the next problem, the XXX being a modern high gain amp built to use 6L6's, it probably is running about 500 volts to the power tubes, way too much for EL 84's, so the power transformer, power supply, bias circuit and probably the output transformer would have to be replaced and redesigned, basically you would have to rebuild the amp, replace all the most costly components and pay someone to do it, I don't really believe you want to go that route, but their are some alternatives we can look at, but I think it is best to warn you now that you are probably not going to be able to get everything you want, first off, yes, different tube brands normally sound a bit different, and alot of manufacturers offer several different variations of the same tube with somewhat varied sound, also some tubes types can be swapped around to change tone, 6L6's, 5881's and KT 66's all fit the same base and wiring, the bias would have to be adjusted but they all work, probably your best bet is to try different pre-amp tubes, 12AX7's can sound very different, some cleaner, some alot dirtier, also pre-amp tubes can be swapped for diferent tubes, see 12AX 7's have a gain factor of 100, you can substitute a lower gain tube, 5751's (SRV favorite) have a gain factor of 70, 12AY7's a factor of 44, swapping in any of those would give a more bluesy tone, and if it was me I would give them a try but no matter what you do I think you are going to be wrestling with a major obstacle, Design, the XXX probably has a very high gain pre-amp design and the master volume circuit design is probably more suited to Metal than blues, you can work around this to a certain degree, try turning the master volume up and the channel volume down, that way you aren't driving the pre-amp so hard, if you drive the pre-amp hard you won't be able to control the crunch to milder distortion with the guitar volume like you want to be able to do and some pre-amp designs are so high gain that it's hard to get anything less than crunch out of them, I think the best advice would be to take the amp to a good shop that is familar with the XXX, tell them what you are trying to do, that you are willing to try different tubes, pre-amp tubes,etc, and see what they recommend, they may even let you try some different tube types to see what gets you closest to what you want, I would look for some one that runs a small shop, loves what they are doing and is good good at it, the larger "Guitar Mega-Store" type places don't usally want to give you the personalized service that you'll want for something like this, I hope I have given you enough information so that you be able to see the possibilities and choices that you have, if you need anything else just ask....................

[Edited by pstring on 09-03-2003 at 01:07 AM]