How do I know if a tube is blown?

Discussion in 'Amps and Cabs [BG]' started by Diggler, Mar 14, 2005.

  1. Diggler


    Mar 3, 2005
    Western PA
    Got my Hartke 7000 out of storage last week, and the tube amp sounds like crap. Very, very weak (unplayable) with lots of noise. When I turn it down the whole way and turn up the solid state amp, it sounds fine. I'm guessing the tube is blown?

    How can I verify this, and where can I get replacement parts for it if this is the case?
  2. basspro2

    basspro2 I'm seeing Gorillas...

    Apr 6, 2002
    Northbridge, Mass
    I believe the preamp tube is shot. It only has one tube and they are really cheap to replace. A 12ax7 is about tops $ 14.00 for a good brand.
    Go to or call Todd Richards at 310-838-3520 he has the best prices and ships so fast it will make your head spin. And no I do not have any affiliation with them just a satisfied customer
  3. jdombrow

    jdombrow Supporting Member

    Jan 16, 2002
    Colorado Springs, CO
    If there is a good music store in your area, you should be able to pick up a tube locally. Most stores carry 12AX7 preamp tubes, since they are very common in guitar amps.
  4. I have a new Hartke 3500 and was thinking of trying a 12ax7. Is it as somple as removing the top and replacing the tube? or is there more to it than that? Also I have seen a 12ax7C What do the letters mean? should I just stick with a 12ax7? Thanx..............
  5. jdombrow

    jdombrow Supporting Member

    Jan 16, 2002
    Colorado Springs, CO
    Yes, just remove the top and replace the tube. If there is a metal sleeve over the tube, push down on the sleeve and twist it. You should be able to see the detents on the bottom of the sleeve.

    A 12AX7C is a direct replacement for the 12AX7.
  6. basspro2

    basspro2 I'm seeing Gorillas...

    Apr 6, 2002
    Northbridge, Mass
    C is a Chinese version of a 12AX7 , Like 12AX7C or 12AX7R for Russian you also have a 12AX7M for a Mullard version which is direct replacement for the vintage Mullard Type tube. They all will work .. It's just the differant type tube and sound variations of each type . Some are warm and some are middey.. Go to the Groove Tube site and read what the differance is..
  7. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    ^^^I've often been told to make sure you hold the tube(s) with a piece of cloth, or thoroughly wipe them down after installing them. The reason being is that you don't want the oil/grease from your hands getting on the tube, and then being "cooked" on by the inherent heat involved with a tube.

    Not sure as to the validity of that, but its something I've gotten into the habit of doing when changing tubes.

    EDIT: To jdombrow
  8. BassGod


    Jan 21, 2004
    On average, how often to tubes get blown? (heh, don't mind the sexual connotations ;)) I was looking into possibly getting a tube amp, but I'd hate to have to replace the tubes often, and it would especially suck if one blew during a gig.

  9. basspro2

    basspro2 I'm seeing Gorillas...

    Apr 6, 2002
    Northbridge, Mass
    It is very true, You will crack the tube if there is oil or moisture from you fingers on the tube they get very hot. Same warning as if you are putting in a quartz lamp in a fixture they give you a wipe to install it so you don't touch it with your fingers.
  10. basspro2

    basspro2 I'm seeing Gorillas...

    Apr 6, 2002
    Northbridge, Mass
    Preamp tubes will last at least a 2 to 3-1/2 years on average or less depending on usage of the amp maybe more. Power amp tubes last about a 1 to 2-1/2 years also dependant on how hard you use it and how long.. like playing 4 times a week really hard etc etc .. Preamp tubes are cheap .. Poweramp tubes are not especially if you own an SVT. Tubes don't just blow up , they wear out from neglect or age or wrong biasing and start to fade in and out and sound like dog $hit, you can avoid alot of problems by just taking care of your equipment and keeping the bias of the amp adjusted right and other things. Just like a car a tube amp needs TLC too, you don't change the oil after awhile your in deep $hit.
  11. I just opened my new hartke 3500 to replacethe tube because someone here said Hartke uses cheapo offbrand tubes and the tube that is in it is a .... Sovter 7025/12ax7WA..... Is there a reson I need to change this tube or is this tube O.K? any suggestions on a better sounding tube? Thanx
  12. basspro2

    basspro2 I'm seeing Gorillas...

    Apr 6, 2002
    Northbridge, Mass
    Sovtek is a Russian tube .. Try a Groove Tube 12AX7M.
  13. protoz


    Nov 30, 2000
    I'm suprised that Hartke is using 12AX7's. I am putting in an EHX 12AX7 into my Hartke 5000 tomorrow evening so I guess I'll see whats in it now. The tube is probably 4 years old now
  14. Thanx for the tips on replacing and other tube types . I just ordered a 12ax7M after reading about it. Silly question you guy's keep different tubes around or just find the one you like and stick with it............
  15. Or it has a smile on it's face :)
  16. Turock

    Turock Supporting Member

    Apr 30, 2000
    and smoking a cigarette.
  17. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Tubes don't "blow", or at least if they do, its spectacular, with "fountains of white fire" inside the glass envelope......power tubes only, btw...

    I'd be more guessing that there is a problem in the plate supply, possibly filament supply.

    It could easily be as simple as needing to wiggle it in its socket....

    One mention.....the silvery stuff inside on the glass has to BE silvery.....if it's white powdery looking, the "getter" is kaput because there is a leak in the glass somewhere.
  18. Diggler


    Mar 3, 2005
    Western PA
    I haven't played the amp in several (more than 5) years.

    If I could ask, how do you neglect a tube? Do you mean dropping the amp and such? And could you explain biasing for me?

  19. Finger Blister

    Finger Blister

    Jul 8, 2003
    Only Power tubes need biasing.

    You don't need to even think about it with a preamp tube.