1. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Silver Supporting Member

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    I don't know about the rest of whoever else is keeping up with this thread but, to me, the most amazing aspect of this forum is how, occasionally as now, you'll come across a discussion by a pair of forumites who both know their s- and you're digging it just being a "fly one the wall" and taking it in. :D
     
  2. John Phillips

    John Phillips Member

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    The interesting thing for me is that although I know what the numbers mean, I tend not to use them much - I prefer to just listen. The math is there as a backup to check that what you're doing is safe for the components (more important for power tubes than preamp) and as a very rough guide, but it can't tell the whole story about what something is going to sound like.

    Things like 'fatness', warmth', 'smoothness', 'grit', 'cut', 'chime' or any number of other terms that can be used to describe what a tube or circuit actually sounds like - in ways that most of us do agree on - can't be accurately (if at all) described or predicted by the cold facts of component specs.

    Or, ...what Mike said :).
     
  3. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Silver Supporting Member

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    Science! true daughter of Old Time thou art!
    Who alterest all things with thy peering eyes.
    Why preyest thou thus upon the poet's heart,
    Vulture, whose wings are dull realities?
    How should he love thee? or how deem thee wise,
    Who wouldst not leave him in his wandering
    To seek for treasure in the jewelled skies,
    Albeit he soared with an undaunted wing?
    Hast thou not dragged Diana from her car?
    And driven the Hamadryad from the wood
    To seek a shelter in some happier star?
    Hast thou not torn the Naiad from her flood,
    The Elfin from the green grass, and from me
    The summer dream beneath the tamarind tree?

    Sonnet to Science
    (1829)

    by Edgar Allan Poe
    (1809-1849)
     
  4. ToneGrail

    ToneGrail Member

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    Is it safe to do this? The folks at the thetubestore.com don't seem to think so.
     
  5. 73171

    73171 Member

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    "She Blinded me with Science!" - Eric Dolby

    The tech talk is fun..but........


    I gotta use my ears to try tubes...I'm 56 years old and my hearing is so bad, nobody else would like the EQ settings I use!

    P.S. I like 5751s in my Princeton Reverb instead of 12AX7s, but I leave the 12AT7 in there.................
     
  6. John Phillips

    John Phillips Member

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    Yes, it is completely safe in almost all cases. There may be slight differences in bias point, so the tubes may not run optimally, but it won't cause any harm to either the tubes or the amp - the power dissipations are too low to fry anything.

    The only exceptions I can think of are things like reverb drivers, where the tube is effectively being run as a mini power tube - it's not always safe (for the tube) to use a 12AX7 in place of a 12AT7, which is higher current- and dissipation-rated, there... although it's still safe the other way round, if the stock reverb tube is an AX7.
     
  7. Swarty

    Swarty Member

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    FWIW, I've never cared for a 12AT7 as an input tube. I find it to be harsh/hollow sounding.. I much prefer a 12AX7, 5751 or 12AY7.

    Also, a 12AT7 is not suitable for a cathode follower (V2 in tweed Bassman, HiPo Twins and 2 & 4 input Marshalls) due to higher than spec cathode voltage.
     
  8. Blue Strat

    Blue Strat Member

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    That's been the general consensus until the Mullard CV4024. Ever try one of these?
     
  9. ToneGrail

    ToneGrail Member

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    Thanks John! I'm planning on swapping out the 12ax7 for a 12au7 in my Valve Jr Head for more headroom. I just wanted to make sure it's safe to do so.
     
  10. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I agree completely about the '80s Mullard CV4024 - it is different than all other 12AT7 types I've tried (about 16 NOS types), including the older Mullard that Mike sells with the "copper getter support." I know of many guitarists who've discovered how musical it can be as a V1 sub for a 12AX7.

    - Thom
     
  11. Swarty

    Swarty Member

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    I'll have to give one a try.
     
  12. skylabfilmpop

    skylabfilmpop Silver Supporting Member

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    Correct me if I am wrong but isn't a 12aT7 dissimilar, ie the two halves are sloghtly different gain values. I always liked the 12ay7 for degaining my SIB Varidrive.
     
  13. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Okay, I will... ;)

    The 12AT7 is specified to have the same gain value (70, vs. 12AX7's 100) for each of its two triodes. I'll bet you're confusing it with the 12DW7 (aka 7247) which is designed to be like a 12AU7 on one side, and 12AX7 on the other.

    - Thom
     
  14. 73171

    73171 Member

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    ...just put a GE 12AU7 in socket 1 (farthest from the rectifier) in my Princeton Reverb....

    NICE!! Very fat sounding and smooooth.......just right for jazz playing...I'll throw a 12AX7 back in there (I've got a Raytheon blackplate coming from Mike K.) when I want to stomp on my Budda Phatman and annoy my neighbors!:dude


    man I love this board...I've learned so much just reading here.........
     
  15. muddy

    muddy Member

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    rather than start a new thread, i'll ask here. what about a pointed stick?

    hehehe... no, i mean howza 'bout using an at7 in place of a 5751 in an amp's fx loop (the loop is intended to run with the latter)? likewize, in a tube delay ped using an ax7 (guya's flip tube/tdx-1)?


    ml
     
  16. rockon1

    rockon1 Member

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    Its easier to try it and see if you like the results rather than give an opinion. In general 12AT7's in place of a 5751 or 12AX7 tends to thin out the sound a bit. Of coarse if this is a desired affect it could be just what your looking for. And also there seem to be exceptions to this like the previously mentioned '80s Mullard CV4024 . In the end let yours ears be the judge. Ive used 12AT7's to clean up somewhat muddy od sounds. Bob
     
  17. muddy

    muddy Member

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    forgot to mention; the fx loop was designed so that you can swap the 5751 for a 12ax7 (minus any fx in the loop), for extra gain, as in adding an extra gain stage (it has send & return vol pots).


    ml
     
  18. Oatman

    Oatman Member

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    This thread touches on a question I hadn't yet asked. (I wanted to read more first) but since it's here:

    If my goal is mostly output tube distortion and little pre-amp tube distortion:

    Is gain or pre-amp tube output (or something else) more important?
    (of course it's a combination, but how can I best understand this)

    I read somewhere that some lower gain tubes like 12AT7, 12AY7, 12AU7 though have lower gain, have much higher outputs (in terms of power or current or what?) and actually slam output tubes harder. This flys in the face of my understanding of the convention, higher gain pre-amp tubes give more pre-amp distortion and faster power tube saturation.

    Help?
     
  19. smolder

    smolder Gold Supporting Member

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    I'm always humbled a bit to have several questions answered in a single thread (by the same folks that i would ask) that predates my curiosity by years. Thanks guys ; )
     
  20. smolder

    smolder Gold Supporting Member

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    I'm short of 5751's and am encourage by the recommendations of the CV4024. I have a handful of 12dw7's, but that is apparently (why I found this old thread) not what I'm after.
     

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