RCA 12AX7 short plate revisited

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by rockon1, Sep 8, 2006.

  1. rockon1

    rockon1 Member

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    Sometimes notions(ill concieved as they might be) get stuck in my head-even though I know its not true. One with pre amp tubes is that "long plates sound better than short plates" Often this might be the case but with that thought in my head I often over look a short plate in favor of its taller brother. Case in point -the RCA short plate 12AX7. Recently took out my collection of these and rounded up a few strong testing,low microphonic ones and plugged them in. In the V-1 of my Palomino they produced a nice "round " tone with relaxed highs and big mids. In the V-2 they seemed to have less hair overdriven and produced a nice fat (not fizzy) OD. Threw a set into my JSX and prefered them to the long plate Tung Sols they replaced! Of coarse different tubes/different amps but,hey, these short plate RCA's are a great choice and probably often overlooked in favor of a lot of other tubes. Bob
     
  2. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Funny, I was just re-visiting my RCA 12AX7A in my collection... 'cause I was considering selling them. I wouldn't agree with the "relaxed highs" notion, from my experience, but I suppose it is all relative. The main thing that sticks out in my mind, for these 12AX7A, is the super-fat lows they produce. I'm talking lardaciously tubby.

    I used to think that the RCA "7025"-labeled short-plates were the exact same tube, just noise-selected. But when I actually tried some 7025, I was surprised to find that they're not the same. The 7025 seem more lean in the lows, more clear in the upper-mids, and less harsh in the highs. Nice and steely. Maybe these are the ones you're referring to? Definitely my preferred version.

    Cheers!

    - Thom
     
  3. rockon1

    rockon1 Member

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    Nope 12AX7A . Different amps/different results? They definately made the high end in both the JSX and Palomino smoother. Maybe not relaxed so much as less extended high frequencies would be a better description? Kind of like turning down a presence control.... As usual my observations are from a high gain standpoint. They really give the JSX a ballsy grind(strong mids) without the sizzle and "high" high end I dont like so much.The description that you give the 7025(which I own a few of) sounds closer to what Im hearing in the 12AX7a's. They definately are leaner in the low end. (I rarely notice or worry about that though as its a guitar and I concentrate on the mids and high end.) The highs are smooth.However mids are stronger.... Im going to leave them in a while. Actually Im running them in all 3 positions in the JSX and a long plate RCA in the PI. Something I rarely seem to do. - Bob
     
  4. Sparky6string

    Sparky6string Member

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    My findings agree with yours rockon1. I can't really tell a difference bewteen the lp RCAs and the sp ones. I have a couple 7025s too but haven't really run them through their paces. They definitely are bassy though. I like 'em, and they used to be my favorites.
     
  5. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Yeah, must be different amp responses. I thought the "mids" were relatively scooped, but that is the upper-mids, not lower-mids. Lows were solid, but fat; highs were definitely bright and less clear than long gray-plate RCA (or 7025). This was mostly in V1 of my Mesa Triaxis, and run from clean through high-gain settings.

    I liked 'em a lot, at first, because of the solid lows. But then I discovered others that were more to my taste.

    By the way, notice the shape of the mica "disks" - they are not circular, but have two opposite sides lopped off, to make parallel lines as you look down on them. That's a good characteristic to identify these tubes by, even if they're branded differently.

    - Thom
     
  6. rockon1

    rockon1 Member

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