76-79 Ampeg V4, Random Crackling, Drops in Volume

Discussion in 'Amps and Cabs [BG]' started by Slaplord88, Jul 30, 2013.

  1. Slaplord88

    Slaplord88 Supporting Member

    Jun 11, 2013
    Hey There,

    I've got a late 70's Ampeg V4. It runs ok, but is unpredictable in behavior. The two problems that seem to randomly appear are:

    1)Crackling/static that seems to be remedied by turning the amp off for a few seconds and back on again. The crackling is random not rhythmic, loud and intrusive on the sound. Once the amp really gets going after playing for 20 min or so, this doesn't usually happen. Often it will happen after initially firing it up for soundcheck. Sometimes I just flip it on and off again a few times and that solves the problem. However an annoying nuisance to stress about when going to flip off standby just before a performance.

    2)Random drops in volume. After playing for any given amount of time, I notice the amp will drop in volume, still playing fine, its like a 30% volume drop. Instantly remedied by turning off the amp and on again.

    Other Note: the amp was solid when i got it, although running very hot. Soo hot that a beer fell onstage and was misting cold beer into the air. The cold beer misted slightly through the grate in the back of the amp and caused a super hot quad of 6550s to immediately crack/blow. Brought to an emergency tech in South Carolina while on tour. He hooked me up with a used set of Sovtek 7027s (of which i have no idea how used they are) and tested himself for a while with no issues. Basically it was just to get through the rest of tour. The first crackling issue occurred on the third night of playing after visiting the tech. He also repaced the standby switch, which was a dinky replacement that was actually spitting sparks out. The power switch is now doing the same thing, I suppose its the same underrated replacement. He also cleaned all the pots.

    I will take this to a tech once I find someone reliable enough in NYC, as i just moved here a few months ago. My band mate tried first flight and was unhappy with the job. New Reverb tank in an old gemini seriously feeding back (any suggestions on a good tech in the city??)

    But just wanted to see if anyone here had any ideas before doing so. I'm not comfortable working inside of a tube amp like this myself.

    Thanks! Kevin
  2. bludog


    Apr 3, 2012
    Brooklyn 11217

    No suggestions for troubleshooting as I just don't have the know-how but if you're in Brooklyn (or even lower Manhattan), Main Drag Music in Williamsburg has a really fantastic repairs department with dedicated techs for amps. These guys really know their vintage tube amps. I've used them for a lot of stuff with great results, check them out. Best of luck!
  3. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    The 7027s if JJ are marginal, and you might have some caps failing.
  4. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    I'd have to think it's either a bad tube(s) or bad cap(s). Finding good techs in NYC shouldn't be a problem, though. It's kind of a music Mecca, after all ;)
  5. I'd start with the switches, sure sounds like bad power switch, based on the OP's report that cycling it off and on helps. (Which incidentally is not a good idea to do with tube amps, at least wait thirty seconds or so)

    A bad plate resistor can cause intermittent crackles. Or bad solder joints, even a cracked PCB trace. Or tube sockets that need retensioning.

    Bottom line, the amp needs to go to the doctor.

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