2:90 retubing questions/thoughts

I bought a new to me 2:90 about a year and a half ago, retubed it when I got it, and I think it's time to be done again. I find that after she's been on for around half an hour, I start having to gradually increase volume, and that I'm losing crispness in tone. So, looking into doing this, I have a couple of thoughts, and would love input from anyone who has done any of these things (as much as I would like to buy three seperate sets of tubes and experiment myself, the bank would likely not approve of this)

1) Can I just retube one side of it? I never use both sides, and it seems like a waste to be burning new tubes that are never going to get used. I've read that it's not okay to just pull tubes from the other side, so I wondered if this would still work for me. (of course not wanting to have any associated tone loss from the older tubes running in the second channel)

2) I've read that it's possible to use el34s in place of 6l6s in the class A slots, which will give me more upper mids and a tights low end, although take away some of the characteristic mesa boom. If anyone has experience doing/hearing this, and could comment on how drastic of a change it is, that'd be fantastic. I find that I can get far more low end than I need with the 2:90 deep switch on, and love pronounced upper mids in my tone, so this could be good.

3) If I do have to replace both quads, can i have one split with el34s and one not? (giving myself a direct comparison option for basically the same money)

4) 5881 tubes. I had a marhsall 9200 poweramp running 5881 tubes, and it was the sweetest sounding thing I've ever heard in my life. Until something blew up 45 minutes after I got it. Had it fixed, but 6l6s were put in it, and she was never quite the same again. Hoping to get a smoother, slightly more compressed tone with those tubes. Again, thoughts/experiences.

Ideally I'd like to replace just one side of the amp with a set of 5881 and el34 tubes. Hoping to get a more present, tighter, smoother tone out of it. Also, enjoy having little things in there that make it sound different (as the gibson/triaxis/2:90/gsystem combo, while amazing, isnt really breaking down any borders in terms of unique tones). And of course buying four tubes instead of eight would be fantastic. I play hard rock, similar in style/tone to Black Stone Cherry.

Any input is appreciated! Thanks!

1) You can retube one side, but I wouldn't pull out the other tubes. Just keep that channel's input disconnected and turn the Level to 0 and Presence to max.

2) Mesa recently put out a letter saying they DON'T recommend mixing EL34s and 6L6s in these units anymore, since the filament current causes the EL34s to operate at a less-than-optimal level.

Mesa Engineering said:

Hi Michael,

Yes, those readings seem correct.

However, we are now recommending to not use EL34's in the 2:90 - as the filament current is higher than we would like to see for EL34's. We recommend ALL 6L6's...

Please let me know if you've got any questions or need assistance in any way. Thanks!

GN

Click to expand...

3) You could do that (if you mean one side EL34+EL34/6L6+6L6, the other just 4x6L6), but see above.

4) 5881 tubes are a drop-in replacement for 6L6s. The tonal difference was probably due to using a different brand of tubes. AFAIK Marshall 9200 used Sovtek 5881, so maybe try those and see if you like them?

You haven't mentioned anything about the preamp tubes inside the 2:90. I shelled out for an octet of =C= 6L6s because my tone was quiet and muddy, only to find out that the tube that actually needed replacing was the input driver. Try replacing the three preamp tubes inside the 2:90 and see what happens. Usually it's a good idea to also replace the PI when replacing the power tubes.

Thanks for the reply

Excellent news on being able to replace just one side of the amp. It's nice to have tubes in there to use as a backup, but I don't need it to sound spectacular, as I"ve never used in the 18 months I've had it (short of hooking it up every once in a while just to see if she still works)

As for the preamp tubes, I replaced all of those when I last did the power tubes, and from what I've read, pre ampers usually last quite a bit longer longer than the big bottles. And as I am at teh end of a typical service life for the power tubes, I think that's a relatively safe bet. But I will likely do the pre amp tubes at the same time as well.


Any thoughts on brands/types of preamp tubes to use? Is getting higher quality ones goingt o make much of a tonal difference? Higher gain vs lower? (I typically am running one side of the 2:90 around 12:00 with the triaxis volume at 4, and a 4-8db drop from the g system)

I have also noticed recently that the presence knob is making a large difference in volume. Moreso than I remember it doing. But that could be in my head.

http://mesaboogie.com/news/2010/08/6l6-vs-el-34-feel-the-power-of-your-amps-power-section/