Best clean headroom: 12AT7 or 5751?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by prof2915, Jun 17, 2005.

  1. prof2915

    prof2915 Guest

    Which tube has the best clean headroom:

    - 12AT7

    - 5751

    I´ve got a 12AT7 in V1 right now (sounds very good) but have never tried a 5751.

  2. Swarty

    Swarty Member

    Dec 16, 2003
    The headroom is negligable, to me the 5751 is a much more musical/vocal sounding tube.
  3. Pedro58

    Pedro58 Member

    Dec 9, 2003
    North Texas
    Depends on amp design, prolly, but my preference is also for the 5751.
  4. prof2915

    prof2915 Guest

    Just tried a JAN 5751.

    Great sound but the tube was extremly michrophonic :eek: was quite surprised with that :( (If I had gain on "zero" an raised the master volume it started feeding back at 7-8... with gain on "zero"!!!)
    when I tapped the amp lightly it went "PIIINNNGGG" :mad:

    My 12AT7 is back delivering great "clean dirt sounds" :D

  5. CAFeathers

    CAFeathers Member

    Apr 17, 2003
    Vacaville, CA USA
    I prefer a GE 5751.
  6. TheAmpNerd

    TheAmpNerd Member

    Sep 23, 2004
    My Fave is Raytheon labeled
    JAN CRP 5751, 63-48
    black plates.

    I've got a small stash of these
    from a military bulk Pack.

    These test out far hotter than
    most "new" 12AX7s.

    And the lot has matched triode
    sections w/in 5 percent!

    These and my Sperry 6V6s
    which are very special RCA
    clear glass Black plates from
    1962 are some of the prized
    tubes in my possession.

    :dude They Rawk

    The Sperry tubes acutally sand blasted
    the RCA octogon off the tubes. I'm sure
    Uncle Sam payed a super premium for these
  7. Rollie

    Rollie Guest

    Yeah, I agree that a 5751 is a great tube, but unless I've misunderstood the question, you want to know what tube will give more clean headroom. 12AT7 has a gain level of 60, and a 5751 has a gain level of 70.

    In my experience a 12AT7 will give me more clean headroom every time. Just try swapping a 12AX7, 5751, 12AT7 and for extremes try a 12AU7 (which has a gain level of 20) in a champ and see what it does to clean the amp up.
  8. TheAmpNerd

    TheAmpNerd Member

    Sep 23, 2004

    And if the 12AU7 it too low, plug in a 12AY7, which has
    a gain of 40 - 44.
  9. prof2915

    prof2915 Guest

    I´ve heard some people say:
    - Less gain= more clean headroom.

    at the same time someone also have said that:
    - the 12AU7 (gain=20) doesn´t have a great clean headroom...

    What is the "truth"?

    Personally I´m very pleased with the 12AT7! (The 12AU7 sounded nice but a bit TOO quiet)

  10. JohnK24

    JohnK24 Supporting Member

    Dec 9, 2004
    North of Pittsburgh, PA
    I don't like the 12AT7 in the V1 spot, as someone said, it's a different type of tube and I find it sounds very constricting, the tone sounds boxed and lacks depth. I use one in my PI slot (Blue Jr. amp).

    I've tried other tubes in V1...12DW7 (a hybrid of 12AX7 and 12AU7) - sort of mellower, lacking some bit compared to a full 12AX7. 12AY7...great for jazz tones, mellow and full bodied tone, but it kills the dynamics of single coil Fenders.

    I do want to try a good 5751 soon.

  11. Blue Strat

    Blue Strat Member

    Aug 2, 2002
    Sterling, VA (not far from Washington DC)
    What OTM said. Due to the much different internal resistance of the 12AT7 you actually get LESS headroom when it's used in a 12AX7 circuit (due to the bias resistor). If you don't believe this, compare plate voltages between the 2 tube types in a 12AX7 circuit.

    This is not to say that you won't like a 12AT7, just that you're liking it for different technical reasons that what you believe.
  12. hustist1

    hustist1 Member

    Mar 4, 2005
    I have a DeVille with a GE 5751 in V1. I tried a 12at7 there and it sucked the life out of the amp. The 5751 sounds great, doesn't distort, and is very responsive. As soon as I find some more I'll be putting them in V2 and V3 and see how that sounds. I tried at7's in V2 and V3 and ended up with _less_ clean headroom than with the Phillips ax7's that were in there before.
  13. prof2915

    prof2915 Guest

    This is what has happened:
    When I had a 12AX7 in V1, my amp went into (preamp) with volume set at "4".

    I then inserted a 12AU7 which stayed clean up to "10", but the loss of volume was to great...

    I then put in a 12AT7 an the sound was great! Punchy, clear and much cleaner than the 12AX7 (breakup comes in at about "7") Didn´t notice ant loss of volume.

    Always use 12AX7´s when I can.

  14. monkmiles

    monkmiles Supporting Member

    Aug 24, 2005
    Greater Boston, MA
    Reviving this topic as I was researching the archives here for info on tube swapping to get more clean headroom...

    I'm looking to swap my v1 preamp tube from a 12ax7 to something for more clean headroom. Ideally I'm looking for a warm yet very clean jazz tone in the clean channel, while also the ability to get a Zeppelin-esque drive in the drive channel. But, I do not want to lose much volume. I'm currently trying a 12au7, but noticing significant volume loss. I have a JJ 12at7 lying around that I might try, but from reading up it sounds like a NOS 5751 might be better as its constructed more like a 12ax7? Thinking/hoping I'll get a little more clean headroom than the 12ax7 and virtually no noticable volume lose. Yet still be able to get the drive I'd like on channel 2.

    So I found what looks to be a good deal for some lightly used GE JAN 5751 tubes on Ebay from TejasTubes and already ordeded a couple to try:

    Right now my preamp tubes (Carvin Nomad) are:
    v1: 12au7
    v2: Sylvania 12ax7
    v3-v5: EHX 12ax7
  15. mmorse

    mmorse Member

    May 12, 2005
    I've tried AT7s and 5751s (RCA smooth blackplates) in my Marshalls and my little plexi clone. I get more clean headroom with an AT7 than a 5751. Having said that, I prefer the 5751 to the AT7. I've tried both tubes in both V1 and V3. I didn't like the AT7 in either position in any of my Marshalls. I liked it in my plexi clone in V1 as it cleaned up the amp a little. El84s can get a little too gainy when pushed IMO. However, I think the overall tone of the 5751 is more like an ax7 and that is what I use in that amp now in V1. It stripped just enough gain yet sounds better than the AT7 to me. Very smooth and sweet top end.

    I also use an RCA 5751 in V3 of my 2204. It takes just enough edge off to tame the last bit of harshness in that amp. I tried GE 5751s but didn't like them much. I think the RCAs are much better. Raytheons are good too.

    Choose wisely with 5751s. Some of them can be very microphonic. The triple mica Sylvanias are supposed to be the bees knees but I've had very good luck with the RCA smooth blackplate double micas. YMMV

    Actually, one of my RCA red labels says Made in Great Britain on it.
  16. twangbanger

    twangbanger Member

    Nov 26, 2005
    Rockford Il USA
    ge5751 5 star sounded sweeter than a rca 12at7 in v1 to my ears.cleaner? dont know but warmer and rounder sounding for sure.Try a couple of each and you decide which you like better!!!!!!!!!!!!!

Share This Page