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!  

My late 70's Ampeg V4 is losing volume; help!

Discussion in 'Amps and Cabs [BG]' started by GreaserMatt, Sep 26, 2010.


  1. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    So, I picked this thing up as a project for $200 a couple of years ago; It had a blown output trans IIRC, and needed a few little things here & there; The tech said the tubes were good, and replaced the caps. All was well until about a month ago, when right in the middle of playing it, the volume dropped off to nothig. Huh!? Then, to make it even weirder, when you crank the midrange knob on the eq, it gets louder. It's possessed, I think, LOL. I don't have any dough to get it fixed right now, is there anything that I can do to try to pinpoint the problem??? I shoulda held out for an early 70's I think... grr... Matt
     
  2. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    100_4594.gif


    zzzz100_4621.gif




    The culprit...
     
  3. KramerBassFan

    KramerBassFan

    Jan 3, 2009
    I don't get it?

    You say its a V4, but i only see two 7027 tubes?

    Or is it the fact it isn't plugged in.... :bag:
     
  4. Get the knobs that go to 11.
     
  5. Soverntear

    Soverntear

    Mar 17, 2008
    Toronto
    hey man ill gladly give you the $200 you invested so you can hold out for that early 70's one :p
     
  6. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    No, theres 4 tubes there...
     
  7. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    What a bunch of jokers on here... LOL
     
  8. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    zzzanimalhouse19.gif



    LOL
     
  9. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    try tapping the tubes when it's on with a chopstick and listen for signs of problems like microphonics or cutting out.
     
  10. mikeldtl

    mikeldtl

    Oct 23, 2005
    Portland, OR
    Anything after noon on the EQ of a V4 is a boost. So I'd expect it to increase in volume. As the tubes are mounted in a hanging fashion gravity tends to work them slowly out of the socket. Try to push and seat all of the tubes (esp. the preamp tubes which have no retainer) back in to place gently first. Give that a whirl and report back.
     
  11. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    The tubes are spread out in the later models. If you're looking at the back there are two on the left, two on the right versus all four on the left like in the earlier models.
     
  12. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    Thanks guys! I'll let you know...
     
  13. KramerBassFan

    KramerBassFan

    Jan 3, 2009
    Oh! I was not aware. Mines a 70', So thats why the confusion sprung up... thanks. Mine was also a Dollar per watt, and still doesn't work :bag:
     
  14. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    as long as all the tubes are lighting up properly, i'd start troubleshooting by replacing preamp tubes one at a time.
     
  15. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    ok
     
  16. rllefebv

    rllefebv

    Oct 17, 2000
    Newberg, Oregon
    Badass rig BTW... Bummer about the problems, but well worth getting fixed. I'll never let mine go!

    -robert
     
  17. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    Hey GreaserMatt, does it act up on both input channels or only 1?
     
  18. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    Both; here's a quote form a local tech:

    I've had similar issues with other late 70s v4s. The issue is likely in the screen/bias supply.
     
  19. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    Ok bros, when I tapped on the tubes, 2 of the power tubes made an audible noise (like through the speakers), & one of the pre amp tubes did the same thing; also, I forgot to mention that there is a low hum going on the whole time its on... I said earlier that the OT trans was replaced, but now I'm thinking it was the power trans; if you look at the back of the amp, it's the one on the left side. Thanks in advance! Matt
     
  20. GreaserMatt

    GreaserMatt

    Sep 4, 2004
    Seattle, WA
    Ok, yeah, they are all lighting up, so I just need to locate some of these weird pre-amp tubes that they use, LOL...
     
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Mar 8, 2021

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.