Do Lower Gain Tubes V1+V2 Make It Squishy?

Discussion in 'Amps and Cabs' started by soundchaser59, Jan 16, 2015.

  1. soundchaser59

    soundchaser59 Supporting Member

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    55 watt EL34 Rivera amp, I have a 12AT7 in V1 and a 5751 in V2. Last night at a gig the amp seemed like it was squishy, not as crisp and articulate and "fast" as I wanted it to be. Not as crisp and fast and precise as the Mesa amp I used to have, for example.

    This is fast funk music with tight rhythms and precise parts. Is it possible the lower gain tubes made my amp not as precise and tight as I wanted? I need it to be just as crisp and fast as I can pick it. It just felt soggy or loose some how. Does cool or hot bias have any affect on this?

    I'll have to go get some new 12AX7's to test my theory......
     
    Last edited: Jan 17, 2015
  2. Bluewail

    Bluewail Silver Supporting Member

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    Personally I really dislike AT7's in a V1 slot. My impression is the same as your - kills the articulation.
     
  3. No457 Snowy

    No457 Snowy Member

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    Your ears are telling you the truth. From Billm's website re the 12AT7:

    "The 12AT7 is the wrong tube to use in a preamplifier stage, even though it’s pin-compatible. It has 60 percent of the gain of a 12AX7, but it’s designed with heavier plates and lower internal resistance to push large amounts of current. The lower internal resistance affects the frequency response of the preamp stage, dulling the highs. Some people like that, but it’s better to use the right tube and turn down the treble control!"
     
  4. soundchaser59

    soundchaser59 Supporting Member

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    Good to know it's not just me then. In fact I think I was trying to compensate for it with my pick hand and arm, and the physical stress and toll on my arm and hand was very noticeable.

    Man, that fits. WHen I had the Mesa with all 12AX7's in it, I almost always played every song with the guitar set on the neck pickup position. Love that sound! But last night I played every song in the bridge position, very unlike me because that position is usually way too bright. But there was no clarity and no presence to the neck position sound, it was just gone.
     
  5. pj1967

    pj1967 Member

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    In my experience 12AT7 works best in the PI position because of its high current output. I think the 5751 in V1 should be fine though...I've tried one in a 1987x RI with good results.
     
  6. Lucidology

    Lucidology Member

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    6L6s will give you what you are looking for regardless of preamp tube choice...
    Maybe a different amp all together ...
     
  7. Blue Strat

    Blue Strat Member

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    Try going back to 12AX7s and play the amp. Then, introduce one of the lower gain tubes at a time and play the amp again. Changing 2 variables at the same time often leads to confusion about what's doing what.
     
  8. Heady Jam Fan

    Heady Jam Fan Member

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    I also think Mesa's are the fastest, punchiest amps. When I want that, I use my Mark III. When I want soft and sweet, I pull out my Fender Deluxe Reverb.

    I use a 12AY7 in V2 of my DR...
     
  9. JB6464

    JB6464 Member

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    A fast and punchy amp to me would be a NMV Marshall (EL34's) about half way up.
     
  10. soundchaser59

    soundchaser59 Supporting Member

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    I will try that, and try the 5751 in V1, but any sign of soggy at the next rehearsal and the 12AX7's all go back in.

    I have no ida if my amp will take 6L6's or not, I'd have to find out from Rivera what the bias change would be. Don't want to do any more mods on this thing to alter voltages, etc. The adjustable boost mods were tedious enough for me.

    A different amp is in the plan, but that's several months away. I should say another amp, because I hope to keep the Rivera.
     
  11. soundchaser59

    soundchaser59 Supporting Member

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    I put all 12AX7's back in, re-dialed in all of my tones, and now I'm back to crisp, accurate, tight sound.

    Thanks!
     

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