I'd STRONGLY recommend changing your tubes the way I did. Wow.

For those curious about what I'm running through this:

Cab: Fender supersonic 212 w/Vintage 30s.
Guitar: Les Paul Goldtop w/57 Classics
Pedals: Boss TU-2, Boss BF-2 Flanger, MXR Phase 90, Boss Chorus, TC Electronics Nova Delay.

Old Tubes: JJ EL34 Power Tubes and Electro Harmonix 12AX7 Preamp Tubes.
New Tubes: Groove Tubes Mullard Reissue EL34 (Rating of 7) Power Tubes and Tung Sol standard 12AX7 Preamp Tubes.

I found that I wasn't overly happy with the tone of my amp anymore. My distortion was just a tad shrill for my liking, the clean channel broke up just a bit too harshly, and the clean channel was also really sterile. Also, I gig about 3-6 times a month, and jam twice as much, so over the last year this amp has really gotten some hours into it. I just bought a new guitar so I didn't want to shell out the dough to buy a new amp just yet. I decided to completely retube the amp instead and hope for the best.

Cost of power tubes: 100 bucks for a matched quad
Cost of preamp tubes: 80 bucks for 4 tubes.
Cost of bias: 40 bucks.
Grand total: 220. Sounds expensive at first...

I had the tech set my bias at 39, which is right in the middle of the recommended range. He told me it was set on the hotter side originally.

Interesting note about Groove Tubes: They have a rating system for their power tubes, from 1 (early breakup) to 10 (late breakup). I play in a ska band, but I like to dig in a bit so I bought a set of 7's.

Improvements in tone:
-I never used to be able to put the bass above 6 without it getting flabby or overwhelming. At jam tonight I was able to put it up to 9 without any issues.
-My clean channel is SO MUCH WARMER. The break up is more gradual and creamier.
-Crunch channel sounds a bit more Marshall-y, but without the uncontrollable icepicks that I tend to hear when playing JCM800's.
-Ultra channel, while still a tad fizzly (just a design flaw, I think), has a lot more meat to it. I am, however, able to up the gain a little more without it fuzzing out on me.
-The attack on this amp is so much smoother and reactive to my playing. It actually feels just a bit slower. I would have thought that to be a bad thing, but it makes my playing sound cleaner and my leads more fluid.

Bottom Line: I may have spent 1/4 of what I paid for this head (1000, and only 2 weeks used at the time!) but I was able to put a HUGE breath of air into my dull and tired amp. I cannot wait to take this out to the clubs this week.

If anybody is feeling the same way about their JSX, I would strongly recommend trying this out. Like I said, I'm in a ska band, but I can hear how these changes would benefit all sorts of styles, particularly classic rock/blues.
Last edited by guitarinchris at Oct 19, 2009,
Sounds good man...I have a 3120 and swapped out preamp tubes for Tung Sols and really, really like them. Amazing what a tube swap can do.
tung sols are my choice of preamp tube because they are so damn musical.

for power tubes I can't say I am a fan of the groove tubes, but the electro harmonix really did me well
My Gear
-Gibson Les Paul Tribute (Bare Knuckle Nailbombs)
-Ibanez "lawsuit" Les Paul (Seymour Duncan Pegasus and Sentinent)
-Ibanez S470 (Dimarzio D-sonic and Humbucker from Hell)
-PRS SE Custom (Guitarforce Black Diamond and Lord of the Blues)

Marshall TSL100
EVH 5150III EL-34 50w
Marshall 1960a cab

Dunlop 535q wah
Boss Super Chorus
Bogner Uberschall
Ibanez DE7 Delay
Electro-Harmonix Power Booster
Fender PT100 Pedal Tuner

Ernie Ball Skinny Top/Heavy Bottom 10-52
EH preamp tubes do not sound good in these amps. Most of the changes you are hearing in your tone are a direct result of the preamp tube swap.
MESA 412