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  1. #1
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    05.24.16 @ 04:02 AM
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    Default 5150 combo problem

    Hey guys

    I have a problem with my 5150 combo I just bought off EBAY. After about 20 minutes of playing it starts with an ungodly crackling sound. Sound like the tubes are bad? Loose? Anyone with similar problems. I paid $600 for this amp too and the seller claimed mint condition with little useage.

    [EDIT]: I forgot to mention I tried different guitar cords and guitars. It also doesn't matter if its on clean channel or dirty or whether or not even any guitar is plugged in. Doesn't matter if crunch or bright is on as well.
    Last edited by Dave King; 02.23.05 at 02:18 PM. Reason: Forgot info

  2. #2
    Eruption mk5's Avatar
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    5150 & 1984
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    04.30.16 @ 02:52 PM
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    First off, check the ground switch and see if that works. Are you playing the amp near neon or flourescent lights? If not and its almost like an "ocean waves crashing" sound, sounds like you have a bad preamp tube. In this case, I'd find the schematic that tells you what preamp tubes go to what and swap each preamp tube with the reverb one (with amp on and reverb off) until you can tell which one is bad. This will require taking the back top section off where the cord wrap is.

    That's my best guess.
    How open-minded do I have to be before my brains start spilling out?

  3. #3
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    03.30.13 @ 08:28 AM
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    Dave, it sounds like a bad preamp tube, or loose tube socket, but it could be a power tube.
    Because you say it starts after about 20 minutes you can pretty much rule out ground or tranny problems. A tranny can heat up and produce a faulty ground or bad connection as it heats up, but there's usually other problems associated with that happening so lets assume it's not that at the moment.

    Here's a an easy check you can do.
    Take the back off the head, and wait till it starts crackling.
    At that point, with the amp still on, use a wooden pencil or wooden chopstick(a chopstick is an amp techs best friend), and lightly, and I do mean lightly, tap each tube a couple of times. That includes power tubes, but start with the preamp tubes. Tap as lightly as you would an eggshell, and tap near the top of the tube.
    Listen for the crackling after tapping each tube in turn.
    If there's no crackling or other odd noise after tapping each tube lightly, then use your pencil or chopstick to gently push the tube, again while the amp is still on. You don't want to really move it, but just push it slightly from side to side to see if it's a bad tube socket.
    If it is, a very slight bit of pressure will produce the noise you talked about.
    As long as you work carefully there's no chance of damage to you or the amp.
    Just be careful not to physically touch anything with you hands because those tubes can get hot.



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