help - how to change eden tube???

Discussion in 'Amps and Cabs [BG]' started by Chad Michael, Apr 27, 2002.

  1. hi talkbassers. how do i change the tube in my eden wt-600?

    my amp works fine now except for the 'gain' knob is a little scratchy when i turn it.

    i wanted to bring a spare tube to gigs, i know i need a 12ax7 series.

    when i look at the amp's chassis, i see about 20 screws that hold the top cover on. is this how to access the tube / socket?? will the internal assembly fall apart if i remove the top (heatsinks, transformers, circuit boards, jackplates, etc)??

    thanks for any advice. (sorry if someone has already covered this in a previous thread)

    bimp (bass, backing vocals, sound system support with 'mister meaner')

  2. rllefebv


    Oct 17, 2000
    Newberg, Oregon
    On my old vt.40, the top panel came off with nothing attached... the tube was easily accessible. You should be fine...

  3. PJR


    Jun 20, 2001
    N.E. PA
    A preamp tube is not likely to just 'go bad' ..... at a gig situation....'s more of a gradual thing.....

  4. I'd be much more suspicious of the gain pot gone bad. I'd change that one first, or at least spray some contact fluid on it.

    A scratchy sound doesn't at all sound like worn out tube.
  5. thanks for the replies.

    i hear that groove tubes are available locally, as well as electro harmonix.

    also that a certain version of a 12ax7 (like a 12ax7R or something) will sound better than other versions.

    any thoughts, tube types??

    thanks -

  6. You'll have to open up the chassis on a WT-series amp. It's not a big deal--just make sure that the power switch is connected properly when you close it up.
  7. 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 think Eden uses 7025's. I just ordered a new one to have "just in case," and it's a Ruby Tube, Chinese. The one that's in there right now is the original (over 6 years old), and it says Eden on it. However, the guts look just like the new Ruby Tube.

    I have tried a Groove Tubes 12AX7 in it, and it worked fine, but didn't sound as "warm," whatever the hell that means. Also, the guts look different, but what the hey, they're all dual triodes.
  8. boogiebass


    Aug 16, 2000
    I agree with Joris. Leave it alone. The preamp tube should, by all practical standards, last the life of the amp.
  9. Yeah.. i mean.. i've got this old tube-powered radio on the attic, which is a mind-bogling 43 years old (!) and it STILL works perfect.

    bought it off a so-called ' yard sale ' for about $ 5.. turns out it's worth 300 times that ( collectors item :D )
  10. tornadobass

    tornadobass Supporting Member

    Nov 20, 2000
    Iowa City, Iowa
    Endorsing Artist: Black Diamond & SuperSensitive strings
    I recall the Eden manual suggests changing the tube yearly...not sure why, though. I tried a few different tubes in my WT-300 and they all sounded the same (not so for my SWR SM-400S, though).

    To change the tube, you need to remove the top cover, which has a bunch of screws. The tube is located close to the input jack and is easy to change.

    BTW, I had Eden go over my amp when I bought it and they added a shield plate by the tube and a new wiring harness with twisted leads that lowered the noise level quite a bit. They also reversed the fan direction to blow out the air rather than draw air in. All that made the amp quieter, for about $100. Worthwhile, I think.

    They didn't change the tube I had in there, though, which was likely the original.

  11. Depending on the circuit, a bad tube with high grid leakage current could cause a scratchy pot. Lots of times scratchy pots are a sign of DC current flowing throught the pot, not just bad contact.

    It may be worth changing the tube to see if the scratchiness goes away. Get yourself an old USA made 12AX7A, and it should outlast you.

  12. Rockbobmel

    Rockbobmel Supporting Member

    Edens like Sovtek 12AX7WA or WB's. I am pretty sure that is what comes stock in them.
    I have tried a number of different ones, but have gone back to the Sov. Currently I'm using a JJTesla. It sounds good. A little darker and lower output.
    I think it will keep the clicky sound down. Less highs.
  13. boogiebass


    Aug 16, 2000
    Maybe it does but I don't think so, amigo. Might wanna check that manual again.
  14. ?? and a non-USA made one will not last as long ?
    obviously you've never heard / used russian Sovtek's
  15. VicDamone


    Jun 25, 2000
    As others here have stated changing the preamp tube is fairly straight forward but for safty sake, unplug any devise your about to service, you knew that. Do not handle tubes with your bare hands.

    An alternative to the 12AX7 is the 5751 series such as the GE JG-5751 (5751 WA), Sylvania Gold Brand (GB 5751), RCA 5751.

    While your under the hood take a look at that gain pot if its anything like my WP100 its plastic and attached directly to a printed wire board (thrifty, very delicate, economical, cheep comes to mind). Be mindful of what you may be using as a solvent to clean with. If a replacement pot is needed I would suggest factory service and have any upgrades preformed at that time.
  16. Funkster


    Apr 6, 2000
    Wormtown, MA
    I had to replace the Vol pot on my WT400, I had it done here at Bose where work! The tech said it wasn't a hard job at all. I also replaced the tube while I was at it with a brand new 1951 GE 5751 and it sounds sweet!
  17. I've heard the Russian stuff. It sounds fine. I just think the old tubes, whether it be made in USA, Holland, England, or Germany, was built better and lasts longer. They were making tons of tubes back then, and they were very good at it.