About two years after I got my first tube amp - a #Marshall JCM 2000 DSL 401 - I decided for no good reason that I need to replace all the stock tubes - stupid! I'm not 100% sure, but I think the stock tubes were all #Marshall branded Svetlana tubes. They sounded great and I had no problems with the amp at all...
So, I read some reviews, talked to some dudes and I purchased a matched quartet of JJ EL84s for the power section and four Tung-Sol 12AX7 for the preamp section.
From what I heard from many people, I was always under the impression that when it comes to headroom and tone shaping, power tubes are more significant than preamp tubes and although it never made much sense to me, I just accepted it.
When I replaced the tubes, the idiot that I was, replaced them all together, power and preamp tubes, so I couldn't tell what was making the difference. Again, stupid! I immediately noticed a difference. The amp was noticeably brighter and had more gain and I liked it, because at the time I barely used the clean channel and more gain was always good for me...
Years later, my amp started making annoying noises. I noticed that the noises come from the clean channel only, so I figured that maybe the clean channel's preamp tube is the source of the problem. So I found the amp's schematics, figured that the clean channel preamp tube is the one that's the closest to the input jack and the one next to it is the dirt channel preamp tube. I swapped them and checked for noise and noticed that the noise was now on the dirt channel only! Problem found, time to change tube!
Tung Sol 12AX7
The tubes I got used to were, as I mentioned before, Tung Sol 12AX7s. For all I know, I considered them good sounding tubes and I still consider them to be great preamp tubes for grittier crunch sounds. However, what I learned from this experience is that they break very early and with my Les Paul or any humbacker equipped guitar, I couldn't really play clean. Setting the gain anywhere below 3 on that #Marshall, sounded dull and lifeless and anything above that was breaking up like crazy...
Anyways, I grew up with this amp, so I learned to love it the way it was and I never thought it had anything to do with the preamp tubes.
Groove Tubes Sovtek 12AX7
When it was time for me to replace that preamp tube, I didn't think too much. I went to my tube stash, pulled one of the 12AX7 that came with my Blues Junior - a Groove Tubes Sovtek 12AX7 tube - and replaced the dead Tung Sol. I turned on the amp and started playing my Telecaster. I noticed a change, but it wasn't very dramatic, so I thought that it's just because that tube it pretty new and the old one really worn out.
One day later I plugged in my Les Paul and started playing clean and I couldn't believe how clean and loud the amp was with the gain dialed to 4! Even when I increased the gain all the way up to 5 and not playing very hard, it was still clean.
I left that tube in the amp for a couple of days until I realized that as amazing as the headroom is, I just don't like the sound of the amp with that tube as much as I did before.. something about it's frequency response changed. The lower mids got muddier and the highs less pronounced and I just couldn't keep it the way it was, so I pulled that tube out and replaced it with one of the JJ 12AX7 from my Blues Junior.
JJ 12AX7
Gain wise, the JJs are between the Tung Sol and the Sovtek, closer to the Tung Sol. And tone wise, they are a touch darker than the Tung Sol, but much more open, even and natural sounding than the Groove Tubes Sovtek.
I ended up with the JJs for ,good several years. I also replaced the dirty channel Tung Sol with a JJ and was happy with the result.
Mullard 12AX7 (current production)
The next tube I tried was the Mullard 12AX7. These have some serious character to them. They are cleaner and warmer comparing to the JJs and Tung-Sols. Have much softer breakup and to my ear sound much richer and three dimensional clean.
It's hard to describe these things with words, so I will just say that the Mullard is my favourite clean channel tube and the Tung-Sol is my favourite dirt channel tube.
you don't necessarily have to replace all the tubes
This experience totally changed the way I approach preamp tubes, and I think that any tube amp owner, should experiment with tubes at some point and the sooner the better.
When experimenting with preamp tubes for tone purposes, remember that you don't necessarily have to replace all the tubes, especially in multi-channel amps.
I would recommend to leave the tube in the amp for some time, play different tunes, with different settings and instruments and only then switch again.
Another important thing that's worth repeating is that if your amp has more than one channel, you might want to consider different tubes to better match the character of each channel.
That's it... now go play some music!
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