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How to tell if a tube is microphonic

Discussion in 'Amps and Cabs [BG]' started by Ralphdaddy, Mar 31, 2005.


  1. Ralphdaddy

    Ralphdaddy Supporting Member

    Nov 6, 2003
    Chicago, Illinois
    First, I did a search and looked through all ten pages and didn't see anything which answered this question. I recently received a Musicman Audiophile HD-500 amp from our very own Planet Boulder, thanks John, and while the amp is the SHIZNIT it has an interesting property or two to it. First, if I tap the outside of the amp, the casing, my cabinet makes a tapping sound. If I hit it harder it makes a louder tapping sound. Sometimes it makes a rattling type sound even though I have the amp sitting on top of my BAM as opposed to my Avatar so it's isolated pretty well from the cab's vibrations... is my poor 12AU7 microphonic? I have an Ei I can replace it with and check it out but I'm just curious what you guys have to say. Also, figure I'll just replace the tube with a few options and see which I like best since they're so cheap... anyone got a favorite 12AU7 for a bottom and midrange heavy tone? I figured I'd try a JJ and an EH, maybe an old RCA... the one in it now is a JAN and I really like its tone but if its microphonic it gots to go. Maybe another JAN then... so many decisions so little money.
     
  2. Ralphdaddy

    Ralphdaddy Supporting Member

    Nov 6, 2003
    Chicago, Illinois
    No thoughts? I know about tapping it with pencil but it's the tapping on the case that has me thrown for a loop, I figured someone would have some thoughts. Where are all of the resident tube geniuses who always help my ingnoramus self out?
     
  3. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    Every time something like that happens to one of my amps, I just take it to a tech :smug:
     
  4. Ralphdaddy

    Ralphdaddy Supporting Member

    Nov 6, 2003
    Chicago, Illinois
    Sheee-it boy! Haven't you ever heard of being "poor" or "attempting to conserve funds"? I'm suffering a bit of both and if I can fix it myself without paying some character 100 bucks I'll do it!! But it's not a bad idea.... :)
     
  5. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    Well... maybe you should suck up to your local tech? :p
    I have known the tech around here for a long time so he fixes all my amps for real cheap.
     
  6. 43% burnt

    43% burnt an actor who wants to run the whole show

    May 4, 2004
    Bridgeport, CT
    I would bring it to a tech. But, I used to work at a guitar store and the tech would test for microphonic tubes by tapping the tubes with his fingernail. With amp on and plugged into a cabinet, tap on each tube. A good tube will have a fuller sound to it. A microphonic tube will have an empty ping sound to it, like tapping on an empty glass bottle.
     
  7. Ralphdaddy

    Ralphdaddy Supporting Member

    Nov 6, 2003
    Chicago, Illinois
    Why do you torment me sir???? Man, if I thought suckin up to the tech would do me any good I'd do it but I don't think I'm his type... too hairy and too manly :smug:

     
  8. Ralphdaddy

    Ralphdaddy Supporting Member

    Nov 6, 2003
    Chicago, Illinois
    That's what I'm talking about brother, I'll just give the old girl the tap test then swap in the Ei and see if anything changes. Thanks guys!
     
  9. Ben Clarke

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

    Jan 6, 2005
    Western NY
    Telefunken and Amperex would probably be exactly what you're after, but are spendy. The good ole $10 RCA clear-top is the bang-for-buck king.
     
  10. Ralphdaddy

    Ralphdaddy Supporting Member

    Nov 6, 2003
    Chicago, Illinois
    Cool, thanks Ben. I'm going to try to go midrange on this one, I swapped in an Ei and it seems to have cleared up all the issues so that JAN went microphonic on me sadly... I figure I'll buy 2-3 different brands and see which I like best. The Ei's not bad, I liked the JAN a lot so I figure I'll try an EH, a JJ/Tesla and maybe an old RCA if I can swing it. Thanks for the advice but the Telefunken's out of the price range right now.
     
  11. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD
    The EH 12AT7s i've tried have all been microphonic, I dunno about the 12AU7s though.
     
  12. Ralphdaddy

    Ralphdaddy Supporting Member

    Nov 6, 2003
    Chicago, Illinois
    Hmmm... perhaps no EH then. I'm not a huge fan of Russian tubes anyways!
     
  13. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    sing into it............................