Ampeg V4 Help! Squealing feedback

Discussion in 'Amps and Cabs' started by battlethesun, Feb 24, 2015.

  1. battlethesun

    battlethesun Member

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    Hey guys, I hope someone here can help this is my first post on TGP. Unfortunately, I'm having some issues with a 70-71 Ampeg V4. I just picked it up a couple weeks ago. Worked fine for the first couple hours I played on it. Sounded great. Still sounds great.. but there seems to be some feedback or interference happening. I power it up, play.. 5 mins in and it just starts squealing, almost popping and the best way I can describe it is a feedback kind of sound. If I tap on the top of the head, it goes away, sometimes. Also, the reverb knob makes a lot of noise.. I just leave it at 0. Sounds goes away. But ultimately over the course of an hour playing this noise happens 5-10 times. Sometimes I can tap the head and it stops, sometimes I have to turn it to standby and back on. That usually does the trick, temporarily. Does anyone have experience with this issue? Any help or advice would be greatly appreciated! Thanks!
     
  2. X–Ray

    X–Ray Member

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    Had four of them back in the early '70s but never experienced this problem and ran them hot and loud...

    Good luck!
     
  3. amphog

    amphog Silver Supporting Member

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    Most likely a tube issue, could be something going on with the reverb, is it unlocked?
     
  4. battlethesun

    battlethesun Member

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    Sorry, I'm actually fairly new to tube amps. I don't really want to open this thing up! haha. What do you mean by unlocked?
     
  5. amphog

    amphog Silver Supporting Member

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    There is a lever like thing on the back of the amp that is used to lock the reverb springs during transit.
     
  6. battlethesun

    battlethesun Member

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    Oh okay I see what you're saying. It was unlocked. But I tapped the tubes and ended up finding out its the 6cg7 tube. I yanked it and it sounded great. I played it for 10-20 minutes and no feedback or any extra noise.. just my sweet tele :D. Ok, so I'll try a new tube. Is it safe to run the amp without that tube?
     
  7. DGDGBD

    DGDGBD Member

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    If the reverb works great once you replace the 6CG7 does the trick, that's great.

    If not...

    I have an early 70s V4 and at one time had a problem with the reverb. It would be intermittent sometimes working sometimes not. Didn't get squeal or feedback though. It turned out to be a faulty cap in the reverb circuit.
     
  8. sharpshooter

    sharpshooter Member

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    Glad that you found the culprit, V4s are finicky amps, complicated curcuit,
    high voltages, and a chassis that traps internal heat,, ideal circumstances for stressed-out parts.
    When they are on their game, they are the greatest, when they have problems they can be a real PITA.
     
  9. DaveKS

    DaveKS Member

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    Now you know what a microphonic tube sounds like, it was probably fixing to go belly up to.

    If I remember it's just used for reverb send, don't quote me on that. Even nos replacements are cheap. I'd pick up a couple those and some 12dw7/7247 and extra power tubes ect to have around for emergency, you more than likely ain't gonna find any of that amps tubes at guitar center.
     

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