Jeff Dunsmore

Preamp Tubes - Guitar Amplifier

Mesa Boogie Trem o verb preamp tube slots

Well, I just got off the phone with one of the best mesa boogie techs in the United States and came up with some interesting preamp tube options. I find it profound that when you talk directly with mesa boogie, they push all thier tubes on us. OK, there is a good reason for it, but mainly for the mesa boogie power tubes because they use a fixed bias. Anyway, when It comes to preamp tubes I find it profound that most of the mesa boogie techs outside of mesa booge always tell us to use different preamp tubes besides the ones stamped mesa boogie on them. Hey, after all, there are only so many tube manufacturers in the world and most of the secondary companies buy them from the same place and test them for specific qualities and stamp there name on them and possibly stamp it with a type or grade. Every guitar amplifier is a little different and for sure, the same preamp tube can sound different in different tube amplifiers, but is based on many other factors. Anyway, we talked specifically about the mesa boogie trem o verb which is the amp I am currently using. Long story short, I have tried a lot of different preamp tubes in my mesa trem. The one he mentioned was Tesla and I have never tried a Tesla Preamp tube in my mesa, so that is what I am going to try next. By the way, I am currently using a combination of preamp tubes ranging from mesa boogie custom SPAX7, JJ 12AX7, and old stock 12AX7 Telefunken.

Mesa Boogie Trem o verb preamp slot task chartThe mesa trem o verb has 6 preamp slots. If you take a look at the mesa trem o verb manual, you will see that each slot has a specific task, or 2 for that matter, because each 12AX7 contains 2 separate triodes. Add to the equation that I am running my V4 effects return and send and use my effects loop master and I have to contend with yet 1 more tube slot that alters my sound. It is very common for me to swap preamp tubes into different slots and try to find the best combination of tubes for all functions of the amplifier. I must note, that for starters, I always test the amp with just the guitar and a cable with no effects upfront or in the loop. After that I proceed to checking out the loop and any effects pedals and cables that I use in front of the amp.

Slot 1

Just a note to self: Tech note - Slot 1 shares the first gain stage and reverb return and mesa said that if you have any type of crossover on the triode, it can cause havoc. For Example: I was getting phase cancellation or some type of mid range sweep sound when I turned my reverb up. The mesa boogie trem preamp tube task chart above even shows you how the V1 B is used for the reverb return. The tech from mesa mumbled something about crossfeedback or crosstalk or something, and I think he was saying that the preamp tube (triode) which functions for two duties was somehow bleeding thru to each other and not doing there job! It is strange to think about a little preamp tube causing such a drastic sounding problem! It was even more of a bummer that it was a brand new mesa 12SPX7 which is suppose to have so much extensive testing done on it.

Preamp tube analysis

Ok, I just got done talking with mesa boogies tech department. I wanted to get some specs on different 12AX7's and other compatible 12A*7 type preamp tubes that I can try with my mesa trem. The trem's input or input gain can be a little tricky. For instance, if you run a guitar with single coil pickups that don't have as much output, you can get a great clean sound out of the amp. Well, for those of us that run humbucker pickups, once again it becomes a little challenging to find ways to clean up the gain stage but find preamp tubes that work for all the channels and options that the trem offers. Here is what mesa told me: They said I could use a preamp tube with less gain and it would calm the amp down a little. Mesa said that the 12AY falls right between teh 12AT and the 12AU. Any of these type of preamp tubes can be used in the mesa trem.

So in conclusion: If I wanted to calm my amp down a bit, I could try putting a 12 AT in my first V1 slot and I am thinking it could be used in the V6 phase inverter slot as well. After looking at the gain chart, I guess it would be safe to say that a 12AU7 in a couple slots could really render a great clean tone while still allowing alot of control of the gain knob on the trem. For me, I concentrate more on HIGH GAIN, but at the same time, I am trying to calm my clean channel down a little, so I will probably experiment a little with the 12AT7 next and hope that I don't loose much gain for my main overdrive/distortion channel and settings. I don't run my gain all the way up on my amp on the distortion/overdrive channel, so I might have to increase it a little and at the same time I am hoping to clean up the little bit of grit that is on my clean channel and still have have it keep the "playability" feel and sound. Don't get me wrong, I like a little bit of grit!! But I hope with a very slight roll off of my guitars volume knob, I can get it ever so slightly cleaner!!!

*worth a mention: I bought 6 mesa SPX7 tubes and stuck them in my amp. Well, mesa says it is just a tube that has had some extensive testing done on it and should be a very reliable tube. My point is this: I played for a while, then took those 6 tubes out and swapped positions around and mercy, I am telling you, my amp sounded different. All the same 12SPX7 tubes with extensive testing, so every tube should sound the same right??? LOL, well personally, I don't think they do!

So, for those of you who use tube amps and just buy preamp tubes and stick them in, maybe this will help you on your endless journey and quest for tone!!!! I will tell you about the experiment my brother and I did with Power Tubes next week!

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