Mark III preamp tubes

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roblowrie

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I should start with the disclaimer that what follows is not scripture; it is merely food for thought.

I have spent a great deal of my spare time in the last month: first researching, then ebaying, and finally trying some new tube concoctions in my Mark III. I may not (ever) be done tweaking and trying new stuff, but at this point I am happier than ever with my amp. I had honestly forgotten just how killer a dialed-in Boogie tone can be.

There is another reason I am sharing my findings here: I referenced this board so many times while in my research phase that I felt compelled to join - thanks all! :lol:

I will describe what I have learned by describing my process as briefly as possible.

I started gigging again recently - after some years of dormancy, my Mk III just wasn't sounding as awesome as I thought it should/could. I realized new power tubes were a no-brainer. So I decided on Winged C 6L6s, got a quartet of them and heard immediate results, especially in the Rhythm 1/2 modes. The lead tone was only slightly improved, however. It was a tad clearer and brighter, but it was still muddy and lifeless.

I was hoping at this point that new preamp tubes would also be a big step up tone-wise...I had no idea!

My decision to go with vintage preamp tubes was based mostly on the ideas that (1) the new ones are only produced in a handful of places and (2) none of them get consistently rave reviews across a range of different amps/guitars/playing styles, while a number of different vintage tubes do. Also, certain vintage tubes are known for producing certain tonal "colors" as well - i.e. RCAs and Mullards are known for their warmth. The new select tubes cost the same as used vintage ones, so...

I got a handful of 12AX7s from the early-mid 60s and a couple 12AT7s, also from the 60s.

The first thing I tried and learned was that I do not subscribe to the "try a 12AT7 in the 1st slot" approach. It takes away the ability to overdrive and compress the input signal, which is precisely what makes this amp so special. IMHO if you are on this road, you might want a different amp altogether.

The next thing I learned was that I would not suggest using any 12AX7s that are know for "coloring" the sound in the first three slots. An RCA in slot 2 sounded great in the Rhythm modes, but blurred the lead. I have found the conventional wisdom of using high-gain low-noise 12AX7s works perfectly in the first 3 slots. I tried a 12AT7 in the 4th slot (Reverb) and it sounds great. I put the RCA back in position 5, and I like its color there.

I have Dutch-made Amperex in 1 and 2, and a U.S.-made Tung Sol in 3 right now, and my amp sounds amazing. The pure Mesa lead tone is back! I would be interested to hear what other Mark III owners using vintage tubes are using.

Cheers!
 
Some of my favorites are:
Raytheon blackplate 12ax7 in v1
RFT 12ax7 in v3
Sylvania 12at7 in the PI slot
 
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