difference between different kinds of tubes

Archived from groups: rec.audio.pro (More info?)

I want to try different tubes for my tube mic-preamp. There are 4
tubes per channel: 2 12AX7 and 2 12AU7. What are the difference
between them and are 12AU7 simmilar to 12AT7. Can a 12AT7/ECC81 be
used in the place of a 12AU7?
14 answers Last reply
More about difference kinds tubes
  1. Archived from groups: rec.audio.pro (More info?)

    "cvsound" <cvrecordingservices@yahoo.com> wrote in message
    news:35de14cf.0407220216.5222b28e@posting.google.com

    > I want to try different tubes for my tube mic-preamp.

    Oh, boy.

    > There are 4 tubes per channel: 2 12AX7 and 2 12AU7. What are the
    difference
    > between them and are 12AU7 similar to 12AT7.

    These are all dual triodes, all have similar plate and filament voltages,
    all have the same pin-outs.

    They primarily differ in terms of gain or amplification factor.

    The 12AU7 has the lowest gain of the bunch.
    The 12AX7 has the highest gain of the bunch.
    The 12AT7 is somewhere in-between.

    > Can a 12AT7/ECC81 be used in the place of a 12AU7?

    With many pieces of tubed audio gear, you can mix and match any of the
    three, and not instantly completely break the piece of equipment, or quickly
    permanently damage the tube. ;-(

    However, the people who designed the equipment, may have actually had
    something in mind when they chose one over the other. ;-)

    Listening tests that don't provide close comparisons to a standard reference
    are often pretty non-critical. Tube swaps are almost never close comparisons
    because there is only one piece of equipment in the test and it has to be
    turned on and off to do the swap. There is often no standard reference,
    because there is only one piece of equipment being tested.

    People will no doubt say that a person has to be deaf to not hear the
    difference something makes, but I've heard that story before and seen it go
    "poof" before my very eyes.. I'm the guy who has done thousands of
    level-matched, time-synched listening tests, and organized hundreds of
    thousands more, and they are the people who have yet to do their first one,
    no matter how easy they can be to do.

    I've never done it, but I've often thought that I could probably mix and
    match these three tube types in some audiophile preamps, and nobody would
    ever reliably hear a difference, particularly if over-all gain was matched
    after the swap. I've never even seen where someone did technical
    measurements to see what technical changes swapping tubes makes.

    I observe from over 50 years of experience with tubes, that while tube
    swapping and tube wine-tasting sessions are popular, and people discuss the
    results of them like they were important truths, I've never seen one done
    using a listening test format that is worth the powder to blow it to...

    San Diego or Baghdad.
  2. Archived from groups: rec.audio.pro (More info?)

    In article <35de14cf.0407220216.5222b28e@posting.google.com>,
    cvsound <cvrecordingservices@yahoo.com> wrote:
    >I want to try different tubes for my tube mic-preamp. There are 4
    >tubes per channel: 2 12AX7 and 2 12AU7. What are the difference
    >between them and are 12AU7 simmilar to 12AT7. Can a 12AT7/ECC81 be
    >used in the place of a 12AU7?

    All of these are dual triodes with the same pinout, but with different
    bias points and different gains. If you substitute one for the other,
    it will not damage anything but it will also not sound very good. Same
    goes for the 12BH7 which is the next tube in that series.
    --scott
    --
    "C'est un Nagra. C'est suisse, et tres, tres precis."
  3. Archived from groups: rec.audio.pro (More info?)

    In article <35de14cf.0407220216.5222b28e@posting.google.com> cvrecordingservices@yahoo.com writes:

    > I want to try different tubes for my tube mic-preamp. There are 4
    > tubes per channel: 2 12AX7 and 2 12AU7. What are the difference
    > between them and are 12AU7 simmilar to 12AT7. Can a 12AT7/ECC81 be
    > used in the place of a 12AU7?

    The most apparent difference is in the gain of the tube. Simple tube
    amplifier circuits such as are likely to be typical of your mic preamp
    aren't like op-amps. In an op-amp circuit, the gain from input to
    output is determined almost entirely by the feedback around the gain
    stage. In a tube preamp, there's usually a little feedback, but the
    gain is more dependent on the gain (mu, or amplification factor) of
    the tube.

    There are other differences, but all of that series has the same
    pinout, so you probably won't blow anything up by substituting one for
    the other. It's not likely that you'll actually like what the "wrong"
    tube does, though.

    --
    I'm really Mike Rivers (mrivers@d-and-d.com)
    However, until the spam goes away or Hell freezes over,
    lots of IP addresses are blocked from this system. If
    you e-mail me and it bounces, use your secret decoder ring
    and reach me here: double-m-eleven-double-zero at yahoo
  4. Archived from groups: rec.audio.pro (More info?)

    Arny Krueger <arnyk@hotpop.com> wrote:
    > "cvsound" <cvrecordingservices@yahoo.com> wrote in message
    > news:35de14cf.0407220216.5222b28e@posting.google.com

    >> I want to try different tubes for my tube mic-preamp.

    > Oh, boy.

    >> There are 4 tubes per channel: 2 12AX7 and 2 12AU7. What are the
    > difference
    >> between them and are 12AU7 similar to 12AT7.

    > These are all dual triodes, all have similar plate and filament voltages,
    > all have the same pin-outs.

    > They primarily differ in terms of gain or amplification factor.

    > The 12AU7 has the lowest gain of the bunch.
    > The 12AX7 has the highest gain of the bunch.
    > The 12AT7 is somewhere in-between.

    I am reading a book on tube amplification design, which I have to say is
    really good since an idiot like me can understand it. Kudos to the
    author. Unfortunately, I am too stupid to remember his name, right
    now.

    Anyway, he has a section on tube model designation systems. The American
    system is very logical. The first number refers to the filament voltage,
    the next two letters to the application, the second number to the
    number of elements and then the last letters to something else.

    So a 12AX7WA is a dual triode (7 elements), with a 12 volt filament voltage.
    The AX refers to its use and the WA to whatever that means.

    (However, I remeber circuits where the filament voltage on the 12AX7s
    is specified at 6.3 volts, so can anyone explain this?)

    An "equivalent" to the 12AX7 is the 7025. Apparently this numbering system
    was a designation that began at 5500 for some reason and each tube was
    given a number in series as they were added to the system. This was an
    industrial grade system which specified a better quality tube. So,
    an old 7025 was actually superior to a 12AX7.

    Rob R.
  5. Archived from groups: rec.audio.pro (More info?)

    On 22 Jul 2004 13:44:22 GMT, Rob Reedijk
    <reedijk@hera.med.utoronto.ca> wrote:

    >So a 12AX7WA is a dual triode (7 elements), with a 12 volt filament voltage.
    >The AX refers to its use and the WA to whatever that means.

    "W" is usually ruggedized. "A" is a revision, often heater warmup
    time controlled, sometimes greater plate dissipation, etc.


    >(However, I remeber circuits where the filament voltage on the 12AX7s
    >is specified at 6.3 volts, so can anyone explain this?)

    The two filaments are brought out to three pins, so can be operated
    series or parallel.


    >An "equivalent" to the 12AX7 is the 7025. Apparently this numbering system
    >was a designation that began at 5500 for some reason and each tube was
    >given a number in series as they were added to the system. This was an
    >industrial grade system which specified a better quality tube. So,
    >an old 7025 was actually superior to a 12AX7.

    7025's had noise performance specified.

    Chris Hornbeck
    "Vote or Die" - P. Diddy
  6. Archived from groups: rec.audio.pro (More info?)

    On 22 Jul 2004 03:16:59 -0700, cvrecordingservices@yahoo.com (cvsound)
    wrote:

    >I want to try different tubes for my tube mic-preamp. There are 4
    >tubes per channel: 2 12AX7 and 2 12AU7. What are the difference
    >between them and are 12AU7 simmilar to 12AT7. Can a 12AT7/ECC81 be
    >used in the place of a 12AU7?

    You might also want to try the 12AY7/6072, a nice bottle but
    out of fashion. And if you want a half dozen 5965's email me
    an address.

    Chris Hornbeck
    "Vote or Die" - P. Diddy
  7. Archived from groups: rec.audio.pro (More info?)

    In article <fkmvf0p43gpr2cd264ptl8r9cqb2c2jsn7@4ax.com>,
    Chris Hornbeck <chrishornbeckremovethis@att.net> wrote:
    >On 22 Jul 2004 03:16:59 -0700, cvrecordingservices@yahoo.com (cvsound)
    >wrote:
    >
    >>I want to try different tubes for my tube mic-preamp. There are 4
    >>tubes per channel: 2 12AX7 and 2 12AU7. What are the difference
    >>between them and are 12AU7 simmilar to 12AT7. Can a 12AT7/ECC81 be
    >>used in the place of a 12AU7?
    >
    >You might also want to try the 12AY7/6072, a nice bottle but
    >out of fashion. And if you want a half dozen 5965's email me
    >an address.

    The problem is that there are a LOT of tubes on the market being sold
    as 12AY7s or 6072s, which don't come close to meeting the original
    specifications.

    I could actually use some 5965s, since I have a pulse generator that
    requires them and won't work reliably with tubes that aren't specified
    with the special grid.
    --scott

    --
    "C'est un Nagra. C'est suisse, et tres, tres precis."
  8. Archived from groups: rec.audio.pro (More info?)

    "Arny Krueger" <arnyk@hotpop.com> wrote in message
    news:3KKdnZlQDIxRBWLdRVn-vg@comcast.com...
    > "cvsound" <cvrecordingservices@yahoo.com> wrote in message
    > news:35de14cf.0407220216.5222b28e@posting.google.com

    > I've never done it, but I've often thought that I could probably mix and
    > match these three tube types in some audiophile preamps, and nobody would
    > ever reliably hear a difference, particularly if over-all gain was matched
    > after the swap. I've never even seen where someone did technical
    > measurements to see what technical changes swapping tubes makes.

    I've done them, although not published the results. In circuits with little
    feedback, changing from one tube type to another, keeping the associated
    components the same, changes the amount of distortion, typically in the
    direction of up, and changes the spectrum of the (harmonic) distortion,
    typically in a direction of uglier (more high harmonics). In other words,
    about what you'd expect from using Tube A in a circuit designed and
    optimized for Tube B. When there's more feedback around the circuit, the
    effects are less prominent. Also what you'd expect.

    Peace,
    Paul
  9. Archived from groups: rec.audio.pro (More info?)

    "Rob Reedijk" <reedijk@hera.med.utoronto.ca> wrote in message
    news:cdogbm$gjk$2@news1.chem.utoronto.ca...

    > So a 12AX7WA is a dual triode (7 elements), with a 12 volt filament
    voltage.
    > The AX refers to its use and the WA to whatever that means.
    >
    > (However, I remeber circuits where the filament voltage on the 12AX7s
    > is specified at 6.3 volts, so can anyone explain this?)

    The 12a*7 tubes all had 12.6V filaments that ran between pins 4 & 5; their
    center-point (these being dual triodes) was connected to pin 9. So you could
    run them from 12.6 volts, leaving pin 9 unconnected, or you could run the
    two halves in parallel, joining pins 4&5 and hooking the 6.3V supply to the
    joined pair and to pin 9. Depended what you had available.

    > An "equivalent" to the 12AX7 is the 7025. Apparently this numbering
    system
    > was a designation that began at 5500 for some reason and each tube was
    > given a number in series as they were added to the system. This was an
    > industrial grade system which specified a better quality tube. So,
    > an old 7025 was actually superior to a 12AX7.

    Better-quality tube in some respect, but not necessarily one which is useful
    in a particular application. Some, for example, were ruggedized versions of
    standard tubes, so they could survive being knocked about in airplanes,
    boats and missiles. Others, like the 7025, were less microphonic, something
    which might be useful to us. Others had controlled filament warm-up time,
    which is really useful only in series-string applications, which nobody uses
    anymore.

    Peace,
    Paul
  10. Archived from groups: rec.audio.pro (More info?)

    On 22 Jul 2004 11:47:41 -0400, kludge@panix.com (Scott Dorsey) wrote:

    >I could actually use some 5965s, since I have a pulse generator that
    >requires them and won't work reliably with tubes that aren't specified
    >with the special grid.

    I'll send you a dozen each GE's and GL-5965's marked GE but look
    like Sylvania construction. Should have your address somewhere here.
    I'd better check 'em first; there're from 1956 and pulls.

    Chris Hornbeck
    "Vote or Die" - P. Diddy
  11. Archived from groups: rec.audio.pro (More info?)

    What's the difference between "smooth plate" vs. "ribbed plate", for
    instance, for the 12AX7 tubes?

    Eric Chang
  12. Archived from groups: rec.audio.pro (More info?)

    cvrecordingservices@yahoo.com (cvsound) wrote in message news:<35de14cf.0407270834.7b393e70@posting.google.com>...
    > What's the difference between "smooth plate" vs. "ribbed plate", for
    > instance, for the 12AX7 tubes?
    >
    > Eric Chang

    It usually specifies an "era" when the tube was manufactured. For
    example, Telefunken "smooth" plates are older than "ribbed" plates and
    command a higher price on the used and NOS market (which is a lot like
    the vintage guitar/amp market). Some people think they sound better ,
    which I can't verify but even if it's true, it's probably not because
    of the smooth plate but because of a number of changes the
    manufacturer made at the time.

    Telefunken is a fine tube however despite all the voodoo surrounding
    it (and Mullard and Amperex too)

    bob
  13. Archived from groups: rec.audio.pro (More info?)

    I will add that I think the ladder plate Telefunkens sound considerably better than the smooth
    plates. But the Dutch Amperex's sound a lot better than either. YMMV.

    --
    Stephen Sank, Owner & Ribbon Mic Restorer
    Talking Dog Transducer Company
    http://stephensank.com
    5517 Carmelita Drive N.E.
    Albuquerque, New Mexico [87111]
    505-332-0336
    Auth. Nakamichi & McIntosh servicer
    Payments preferred through Paypal.com
    "Bob Chandler" <bassface@pacbell.net> wrote in message
    news:da316040.0407280252.3279d8de@posting.google.com...
    > cvrecordingservices@yahoo.com (cvsound) wrote in message
    news:<35de14cf.0407270834.7b393e70@posting.google.com>...
    > > What's the difference between "smooth plate" vs. "ribbed plate", for
    > > instance, for the 12AX7 tubes?
    > >
    > > Eric Chang
    >
    > It usually specifies an "era" when the tube was manufactured. For
    > example, Telefunken "smooth" plates are older than "ribbed" plates and
    > command a higher price on the used and NOS market (which is a lot like
    > the vintage guitar/amp market). Some people think they sound better ,
    > which I can't verify but even if it's true, it's probably not because
    > of the smooth plate but because of a number of changes the
    > manufacturer made at the time.
    >
    > Telefunken is a fine tube however despite all the voodoo surrounding
    > it (and Mullard and Amperex too)
    >
    > bob
  14. Archived from groups: rec.audio.pro (More info?)

    For those of you who have been asking, it is "How to service your own tube
    amp" by Tom Mitchell.

    Rob R.

    Rob Reedijk <reedijk@hera.med.utoronto.ca> wrote:

    > I am reading a book on tube amplification design, which I have to say is
    > really good since an idiot like me can understand it. Kudos to the
    > author. Unfortunately, I am too stupid to remember his name, right
    > now.

    > Anyway, he has a section on tube model designation systems. The American
    > system is very logical. The first number refers to the filament voltage,
    > the next two letters to the application, the second number to the
    > number of elements and then the last letters to something else.

    > So a 12AX7WA is a dual triode (7 elements), with a 12 volt filament voltage.
    > The AX refers to its use and the WA to whatever that means.

    > (However, I remeber circuits where the filament voltage on the 12AX7s
    > is specified at 6.3 volts, so can anyone explain this?)

    > An "equivalent" to the 12AX7 is the 7025. Apparently this numbering system
    > was a designation that began at 5500 for some reason and each tube was
    > given a number in series as they were added to the system. This was an
    > industrial grade system which specified a better quality tube. So,
    > an old 7025 was actually superior to a 12AX7.

    > Rob R.
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