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12 AX7s Please explain

Discussion in 'Amps and Cabs [BG]' started by Dan Muller, Nov 16, 2002.

  1. Dan Muller

    Dan Muller Guest

    Sep 28, 2001
    Baltimore, Maryland
    Can someone please explain the differences between 12 ax7's, 12ax7A's and 12 ax7C's, etc. I have an Ampeg SVP Pro and i think it could use new tubes. It is only a few months old and it has never been gigged. When it is turned on, a sound comes through my speakers like rustling or wind almost, even when the preamp is muted. It is NOT the poweramp and is NOT the speakers or cables. (Perhaps it could be something with my house's electrical system?) Anyone who can help please give me your input.

    Thank you

  2. Pre EB

    Pre EB

    Mar 15, 2002
    Denton, Tx
    My F-1X is having the same problem! only I compared the sound to the ocean.
    SOMEONE HELP US BOTH!!!! I'm on my 3rd tube and this thing sees LIGHT use.:( :confused:
  3. Do a search for preamp tubes. Lots has been said on this topic, especially this past summer. Look for comments by Chuck Moses or swappin' preamp tubes in Mesa M-2000 amps. Some bottles rock, some don't don't. Many dig the JAN 12AX7WA's, I liked my Mesa labelled Sovtek 12AX7EH's for their toothy snarl...you might not.Keep looking, detailed descriptions you will find!

  4. jobu3

    jobu3 Artist formerly known as Big Joe

    Feb 17, 2002
    Mountain Top, PA
    as long as it says 12ax7 it will work for you.
    don't worry about the letters after it, they are mostly just to say where it was manufactured.
    (r=russia, c=china, a=america etc.)

    as for the differences btw. each model use the search as mad subwoofer has stated...
  5. Pre EB

    Pre EB

    Mar 15, 2002
    Denton, Tx
    Yeah but what about the problems Dan and me described? Is the tube the problem? I'm on my third one in about five hours of use:confused:
  6. Try re-wording your original thread title and see if you get some more specific hits?
  7. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    The sound you are describing could be caused by a noisy tube.

    12AX7-The original designation for that tube type.

    12AX7A-Same tube with a spec for lower microphonics.

    ECC83-European nomenclature for the 12AX7(A)

    7025-Low noise version of the 12AX7A.

    6881-12AX7A designed for mobile use-a bit more sturdy construction.

    5751-Pin for pin replacement for the 12AX7 but has a spec of 70% of the gain of a 12AX7. These tubes were designed for avionics and use in tanks. Usually have subdued highs.

    Through the years many companies have used different designations on tubes. Groove Tubes used to sell NOS USA made tubes marked "GT 12AX7A". In this case "A" meant American. GT has used similar markings on other tubes-"R" means Russian.

    Another problem that can make tube identification difficult is that manufacturers frequently bought tubes from other manufacturers and marked them with their own name. A tube marked "RCA" may actually be a Sylvania. A tube marked "GE" may be a Mullard.

    When manufacturing of tubes was phased out in most countries due to the heavy metal polution, some tubes were remarked with fake markings to indicate a more desirable country of origin. If you see a tube marked "Made in England", it is almost certainly a fake as the real GB made tubes are marked "Made in Great Britain".

    Many players balk at spending $50 for a NOS tube. They will, however, off their preamp for another brand and spend a lot more $$ in the process. Some preamp designs can go from almost unusable to wonderful sounding with the change of the tube(s). Tubes are the cheapest wonderful tone you can buy. Think about it.

    Feel free to email me if I can be of help.


  8. Big String

    Big String Supporting Member

    Apr 22, 2000
    Northwest Indiana
    What would you think of Sovtek 5751 in a Demeter VTBP201s? Still subdude high...?? I bought some on a recommendation but have not installed yet.
    Thanks for your oppinion.
  9. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    I have not tried the Sovtek 5751. I recommend you try them and see what you think. That is what really counts, your opinion formed with your ears.

    FWIW, I have 5751's made by Sylvania, RCA and GE and have tried them in my preamps but prefer other tubes to the tone I get with the 5751's. If anybody is looking for some NOS 5751's I'll sell mine for less than what dealers charge for them.

    The only Sovtek tube I've tried that sounded good to me was the 12AX7LPS. The 12AX7LPS has nice detail in the highs and lacks the harshness of most recently manufactured tubes. The EI 12AX7 is also a nice sounding tube.

  10. ebozzz

    ebozzz Supporting Member

    May 17, 2001
    I like them also but I don't have a wide range of tube experience. I sent you email earlier today Chuck. The quote above helps me regarding the question that I posed to you in my message. Thanks!
  11. Paul A

    Paul A

    Dec 13, 1999
    Hertfordshire U.K!
    The sound you describe sounds like a tube going "microphonic".
    Pretty simple to check which one.
    Open the amp, switch on and gently tap each tube in turn with the end of a pencil or something similar.
    You'll hear the "tapping" clearly through the speaker when you find the culprit.
    Oh......DONT stick your fingers (or any other part of your anatomy!) in there, it'll hurt ....lots.

  12. cjlbass


    Nov 15, 2002
    I have been hearing a lot of good things about the Electro-Harmonix tubes lately, one of the guys I work with retubed his Marshall TSL100 head with them, and proceeded to geek out, and his head did sound a lot better than the stock tubes that Marshall used. He did pre- and power tubes so take that for what its worth.
  13. Yeah what about Pre EB being on his third tube? I don't get that one...something in the circuit toasting his bottles??
  14. Paul A

    Paul A

    Dec 13, 1999
    Hertfordshire U.K!
    "Yeah what about Pre EB being on his third tube? I don't get that one...something in the circuit toasting his bottles??"

    I just got through FIVE tubes (EH,Sovtek) trying to find a decent non microphonic one...... I guess the quality control isn't there these days.....
  15. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    I swapped out the stock 12ax7 in my Eden Navigato preamp with a Sylvania 5751, and it made a WORLD of difference in the tone, much, much better, and the tube gain knob now adds more of what I would describe as punch instead of grit.
  16. Pre EB

    Pre EB

    Mar 15, 2002
    Denton, Tx
    Still haven't gotten a new tube for my F-1X; I've been practicing through my Bassman that mysteriously "healed" and now sounds great again:confused:
    Is the 12AT7 another version of a 12AX7? What's the difference? I found a JAN 12AT7 at a shop here and was wondering if it would work. I like the concept of Joint Army Navy thing. More durable, right?
  17. iammr2


    Jun 10, 2002
    Here's a copy of a reply I received from GT about a tube in an SWR:

    Yes, the 12AX7 and the 7025 are technically, and electronically the same part. However so are any two 12" 8 ohm speakers...and we know how different two speakers can sound. The same is true with preamp tubes... However, we offer at least 5 interchangable 12AX7 type tubes, each will have it's own sound and tone for you to choose between. Since there is only a single tube in your preamp, this is easily accomplished by just changing and listening to the result. Look at our web site for a brief description of the following options available to you:
    12AX7A (old USA Stock, solid tone and long life)
    12AX7C (a new offering from China, warm round and fat tone, not too bright)
    12AX7R (lder style Russian type, strong tone but a little edgy)
    ECC83 (European, very linear, or true, tone...might be best bet for bass)
    7025 (Yugo made, big bottom, high gain nice top end too, also good for Bass)

    Used to have a document describing each tubes' gain and sonic character. I'll see if I can find it.

    As far as the amp making unwanted noise, why don't you just take it to a tech and have it repaired?
  18. Pre EB

    Pre EB

    Mar 15, 2002
    Denton, Tx
    Thanks for all the help, guys.
    As far as taking it to a tech, I'm hoping that it is just a rash of bad tubes. $$$ is pretty short right now and if it is just a tube then I save some. I'll try ONE more tube and if it does the same thing, I will take it to someone qualified to work on it.
    On a side note, has anyone ever forwarded a thread like this to a manufacturer? Think if this was forwarded to Alembic, they might help or have suggestions other than the fine advice I have recieved here?
    PS I hope dan got some help too!:)
  19. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    I once called Alembic about a problem I had with a preamp and they connected me to Ron Wickersham. He was very helpful.

    Email me and I'll send you a tube that I know is good.


  20. PJR


    Jun 20, 2001
    N.E. PA
    Listen to Chuck......he knows his '****e' when it comes to tubes !!!

    I replaced the stock Preamp tube in my SWR Mo-Bass.....with a Telefunken (sp) ECC83 ( model # I think...)

    Big , Big difference to my ears......Tone fuller , richer......yea, the 1 tube cost about $90 shipped, but a small price in my book for the improvement !!


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