1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

Is there a tube that will yield higher gain than a 12ax7???

Discussion in 'Amps and Cabs [BG]' started by panic_striken, Dec 29, 2005.

  1. panic_striken


    Oct 13, 2005
    I read in a post on another forum that 12av7 will actually get higher gain.........any truth??? How are the Tung-Sol 12ax7's???
  2. Bob at Eurotubes can get you a JJ 12AX7 that has higher gain than normal. I thought about it myself to get more distortion from my hybrid, but laziness won out.
  3. Le Basseur

    Le Basseur

    Mar 26, 2002
    The short answer is no.This is for a given standard voltage gain stage,as founded in your Fender/Marshall/Eden/whatever amp.A 12AX7/ECC83 has a Mu (amplification factor) of 100,the biggest value in the small,noval double-triode world.
    The longer one is yes.There is a specific v-gain stage schematic that uses a non-standard configuration (a double-triode wich uses both halves in a rather non-conventional manner) wich gives a Mu of 200 or greater,depending of the used tube and/or specific passive components' values implied.However,this is more of a guitar amp tech's issue,as it requires advanced skills.
    The 12AV7 is a moderate current (9~18 mA), medium Mu (37~40) noval double-triode,as opposed to a 12AX7 (1,2mA/100 Mu).It can be used in a guitar/bass amp but due to it's characteristics,it's an entirely different flavour.
    Wich one of them?
    THE TungSol (only NOS samples,scarce and expensive) are great but they're out of production.
    The new TungSols are rebranded Russian copies of the US originals (not bad,sometimes really good) or Chinese stuff (still crap...maybe,in the future...).There were some rumours about some newly US-produced TungSol tubes but personally didn't see nothing original (US-made according to older specs),I mean REAL tubes,not Internet pics/hype.However,reviving a dead industry is a tough job nowadays due to the much higher environmental issues AND lack of highly-skilled,qualified personnel.
    EuroTubes is a great deal (very serious dealer,measures and matches stuff) but no one can pretend selling some 12AX7's,being JJ Tesla or anything else,with a gain higher of 100!!!
    What Bob says is that if you want the highest posible gain,he can sell you samples that really have Mu 100,as opposed to other 12AX7's wich have a slightly less gain (it happens all the time....these tubes are not defective,it's a mass production issue).
    If you want more distortion,simply go to an amp tech and ask him to build for you a multiple,cascaded gain stage preamp (e.g.as seen in Mesa Boogie guitar amps) or,if your existing amps permits,to lower the anode voltage(s) of a given tube.Or,use pentodes.Or,buy a stomp box.Or,... :)
    Le Basseur
  4. Trevorus


    Oct 18, 2002
    Urbana, IL
    A 12ax7wb I think tends to have a crunchier nature, but they tend to be microphonic. I had one in my tube guitar combo, and it did nothing but a constant whining tone. It didn't start out that way, and it sounded good at first, but all the tubes I have gotten from a local dealer have been crap. I haven't bought from them since.
  5. Yup, ive got them in my SVT-II's preamp :)
  6. zombywoof5050


    Dec 20, 2001
    I'm pretty sure that the 12AX7A is purported to be a 'higher gain/lower noise' version of the standard 12AX7.
  7. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Does the gain of the tube really affect the gain of the circuit? I thought that the overall voltage gain was largely determined by the ratio of the plate and cathode impedance in a typical Class-A circuit.
  8. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Nope, the equation for a typical (bypassed cathode resistor) common cathode Class A gain stage is: Av = (mu * Rp)/(Rp + ra) .

    Take a look here, in the "Advanced Tech Info" section: http://www.aikenamps.com/ .
  9. zombywoof5050


    Dec 20, 2001
    I don't know for sure, but it stands to reason (in my mind) that a higher gain tube will provide more gain. It doesn't neccessarily mean that all 12AX7A's will have higher gain than all 12AX7's. But perhaps the 12AX7A of a particular manufacturer will have more gain than a standard 12AX7 from the same manufacturer (who knows?)
  10. 7025 ?
  11. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    I've read in several separate places that the 7025 is a higher-gain version of the 12AX7.
  12. zombywoof5050


    Dec 20, 2001
    I've heard that the 12AX7A and 7025 are pretty much the same thing. In fact, I have some tubes that have 12AX7A/7025 stamped on them.
  13. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Hmmmm, OK, if the 12AX7A ia a higher gain version of the 12AX7, then I guess the 7025 would likewise be a higher gain version, eh?
  14. Kelly Lee

    Kelly Lee Yeah, I'm a guy! Supporting Member

    Feb 17, 2004
    Marana, AZ, USA
    So would the new Ruby STR 7025 'Silver Special' be considered a higher gain tube than standard 12ax7 tubes? If so, has anyone tried them?
  15. A 7025 is a low-noise 12AX7. It has no higher gain.


    Nov 24, 2001
    New York,NY
    ...I LOVE my Estey/Mullard 7025's...

  17. zombywoof5050


    Dec 20, 2001
    Thanks for the info, and sorry for giving misinformation. I was going by what Lord Valve told me over the phone. It's possible that he was only referring to the particular tube brand we were talking about, and that I erroneously took it that all 7025's were 'higher gain/lower noise' (or maybe he was just trying to sell me some tubes-lol).
    Thanks again.
  18. Lots of interesting (and not always correct) information in this thread.

    Concerning the question of a "higher gain" tube than a 12ax7, please check out this article:

    preamp tube article. The article is geared toward guitar amps, but the science/thought behind the discussion is very sound.

    The bottom line is that there is a VERY large variance in actual gain between tubes of the "same" type. Basically, the standard 12AX7 spec that applies to 12AX7 / ECC83 / 7025 tubes, has a reference of 1.2 mA at 250 volts with a -2 volt bias. However, within the same manufacturer and type batch, you will find tubes that may range from .8 to 1.4 mA at that current/voltage. This is a difference that you will hear immediately and makes a noticeable contribution (or subtraction) to or from your preamp/amplifier's sound.

    If you have the luxury of being near a reputable tube vendor, my advice is to have some tubes tested for mA and/or mU before you buy. If you know a reputable seller that will provide you with good reference numbers prior to a sale - count yourself lucky and go with a good high gain -AX7 tube if that's what you're seeking.

    Please remember that higher gain does not always equate to "better" sound - especially with a bass preamp/amp. Often higher gain preamp tubes will also have a higher noise floor amplified through both stages of the tube...this is also something you will hear (and probably not like). In many cases, a 12AT7 or a 5751 preamp tube works much better for bass preamplification (slightly less gain, but typically very clean and controlled). Different tubes sound better in different amplifiers - it takes some testing and "rolling" of tubes to find the best match. As an example - do a search for preamp tubes in this forum and you'll find several "show-downs" that members have done. Of note, Tombowlus did a very nice review of several tubes using his fine collection of preamps some while back.

  19. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Tubes are cool.