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NOS RCA Blackplate 12AX7 vs. GT 12AX7M

Discussion in 'Amps and Cabs [BG]' started by LoveThatBass, Dec 30, 2004.

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  1. Mike Kropotkin suggested I try the NOS RCA 12AX7 in my SWR 350x amp. Here is how it compares to the 12AX7M.
    While the 12AX7M is a good tube for new stuff..the RCA Blackplate is superior in most ways. Very low noise level, excellent clarity, good tight low end...better mids and upper frequencies. This tube cost twice what the 12AX7M cost, however if it lasts half as long as many NOS RCA's are reported to it will have saved me approximately 4-6 of the newer Groove Tube M's. They are reported to last about a year before the tone starts to wane. When put in this light...it seems well worth the money...certainly does for tone and noise level.


  2. The trouble with NOS RCAs is that they are not consistent. A good one is superb, better than anything, but you take the risk of buying one that's mediocre. The GTs on the other hand have a minimal failure rate. If you can get a return policy on the RCA, then that's the way to go.
  3. Ummm NO.... Most RCA's ARE consistently great tubes. In all my years, I have YET to come across a bad RCA 12AX7 new or used. GT's Chinese "Mullard" OTOH, has a terrible reputation for reliability and build quality.
  4. Ostinato

    Ostinato Guest

    Feb 7, 2005
    Toronto ON
    The GT Mullard is a POS.

  5. Your right!!!
    And the RCA Blackplate is a POS +++
  6. Please explain... I meant what I said. In over 14 YEARS of fixing amps, I've NEVER encountered a bad RCA 12AX7.
  7. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    Y'know, outstanding NOS 12AX7 are really pretty affordable, considering their long life. One year? That seems short in my experience. Spend $40 on a Tele, and change it when you sell the amp. (Then put it in your next amp!)


    Nov 24, 2001
    New York,NY


    PS: I have a few NOS RCA 12AX7/7025's black plates that sound pretty damn good in my Trace V-8...
  9. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    Really? I've never heard of preamp tubes wearing out that quickly, many of them seem to outlast whatever amp they reside in.

  10. Maybe he misread ?

    Manufacturers usually say a year for an often played power amp tube, and is it not something like 4-5 years for the pre ?
  11. ...and they GREATLY exaggerate this need. Even modern produced tubes will last decades, preamp AND power tubes. If you play through your amp regularly for 30 or so years, you MIGHT have to replace a set of power tubes ONCE and the preamp tubes should be good for at LEAST another 30.
  12. Nightbass


    May 1, 2001
    Seattle, WA
    I bought two NOS, and one of them introduces a very loud 60Hz HUMMMMM into the pre. If you want a rare bad one for your collection, I'll send it to you in trade for a good one. :)

  13. Blue


    Jun 19, 2004
    Central NC
    The problem may be ... what is NOS. A snook can take a bad tube and call it what he wants. If you dealing with Mike K., I doubt you'll have a problem.. he's a pretty square guy.
  14. There are several counterfeit "RCA" 12AX7's out there. Some were made in Yugoslavia, some in China, some in "Jugoslavia" (no kidding- that's what they say) ect, ect. When I say "RCA" I mean made by the Radio Corporation of America IN America and verifiable as such.
  15. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    This seems like quite a sweeping generalization. That is, unless you are referring specifically to the SWR, and they have some magical physics-defying technology that no one else has. 60 years from any tube in any bass amp is very unlikely. Let's be realistic here.
  16. It seems like the fiftieth time I've had to say this. No, that is NOT some "sweeping generalization." It is bonafide fact. For all you people out there that swear tubes are just waiting to die any minute, can you please enlighten me as to what physical property that would have to be 'magically defied' or a tube "dies?" Aside from a short, or physical damage, or an amp malfunction, there is only ONE way a tube "expires." I know what that is. Do you?

    If you doubt my veracity, perhaps you could check with the myriad other posters here running various vintage amps on their original tubes. BTW regarding:

    I know it's ONLY 51 and 41 years respectively, but my Altec 342B is running its original tubes from 1954 sans a shorted rectifier and a cracked driver tube sustained in a fall, and my wife's 1964 Fender Vibrolux Reverb is chugging quite happily on its stock tubes. You want any more realism?

  17. Maybe I do not understand what you are trying to say.
    I meant the NOS RCA 12AX7 Blackplate was considerably better than the 12AX7M Mullard copy.
    Sorry for any confusion here.
  18. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    Congratulations. Your username suits you as well as mine does me. Back your info up, then. Why make me ask? I'm not saying that tubes are delicate flowers that must be handled with kid gloves, but c'mon...

    Folks with brains don't expect tube life that long even in my Mc30's, famous for being easy on them.

    Saying something fifty times doesn't make it true, Dorothy (there's no place like home...). Go ahead and school me, and I'll eat my words if you prove me wrong.
  19. You REALLY want to go that route? :rollno:

    Aside from the obvious implication that I'm lying about the age of the amps and the tubes in them I previously mentioned, I take it to mean you want to know what dies in a tube. Easy, but I'll get to that in a minute...

    You spoke with such resounding authority I figured you at least had a cockamamie theory as to why they die and I wanted to hear it. Sometimes, tube myths can be downright amusing, especially from those who "know better" than the truth.

    Believe what you like. You're entitled to it. Don't let the fact that the physical laws that you referred to previously contradict you completely have any bearing whatsoever.
    (Emphasis mine)

    Folks with brains don't have YOUR MC30's. ;)

    I quite agree. You're also quite misinformed and sadly seem to revel in your ignorance to the extent that you're forced to post stale insults rather than actually levy some sort of argument as to why tubes aren't as long lived as I've said. IOW, your bad jokes can't cover for the fact that you have no idea what you're talking about.

    OK, session's in: cathode wear- you know what that is, right? Most tubes are NEVER going to completely emit every free electron from their plates, so you're not going to see a tube completely neutralize its plates from use. Since the most of the other internal elements are of even lower emission, that lets the various grids off the hook as well (barring shorts of course). That leaves two things; the envelope's physical integrity; leaking air WILL literally burn a tube's insides but that falls under the category of damage and the cathode- which is our "villain."

    Since the cathode is the first element in a tube to see a voltage swing it will naturally emit quite a bit; how much depends on various factors (cathode resistor value, heater temperature, nature of input signal, etc). At the end of a tube's life, the cathode begins to run out of emission. It's just a coil of tungsten wire wound around a support post and is less than 1/1000th the size of the plate. Eventually, it simply cannot emmit. It's out of electrons, and even though the heater heats and the plates are full of free electrons, there's nothing to knock them into current. Takes about 60,000-100,000 hours full duty cycle.

    Since you're so proud of your MC30's, I'll tell you what 'kills' your 6L6's every few years: they're improperly biased. Those brown spots they have on the getters, those are oxidation burns where trapped gases from the tubes' manufacture have literally caught fire. That oxidation increases cathode wear by a large order of magnitude because the oxidized gas absorbs the emitted electrons and you have to turn the amp up to get the same level of previous volume. To compensate, you bias the tubes 'hotter' and their gain returns to normal, but the higher plate current wears the tube even faster.

    That's what goes on with power tubes anyway. If you're killing(and I mean dead- not BS audiophool 'they don't sound as good' dead) preamp tubes, you need a larger cathode resistor on them, but then your 30 watt amps wouldn't sound like 60 watt amps anymore.

    How would you like your words, medium-rare or well done?

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