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  1. #1
    Little Dreamer sixstringer's Avatar
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    06.20.17 @ 06:59 PM
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    Default 5150 III Problem

    Hope everyone is having a great holiday season....I am not much of an amp expert, but am hoping one of you can give me some advice before I take my 5150 III into the shop.

    Powered her up last night and channel 1 and 2 are sounding very weak and thin. Channel 3 seems normal. Getting a little distortion out of channel 1 at low volumes as well.

    Over the past few months, channel 1 was sounding a little weak and grainy after initially powering up the amp, but would be OK after switching to a different channel and coming back to it after the amp warmed up for a while.

    thanks for any advice you can give

  2. #2
    Eruption LeftyVanHalen's Avatar
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    Default

    Sounds like a bad tube. You might want to get some 12ax7 tubes and replace the ones in the amp. If that doesn't work...then it's power tubes and will require a tech to bias the amp.

    Hope that helps. Good luck

  3. #3
    Eruption donkost's Avatar
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    12.10.17 @ 08:16 PM
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    Default

    Yep, Lefty beat me to it... Regardless of tube amp, I think the first thing to try in situations like this is to insert a spare 12AX7 in the first V1 position (should be six 12AX7 tubes). That one usually has a metal cover on it. Since the other preamp tubes cascade off that one it can have the highest impact on sound if it's bad. If you have no spare 12AX7 tubes you can usually even swap the position V1 12AX7 tube with one from a different position, like V6. Once again, if the sound perks up it means the original V1 12AX7 tube was bad. I just looked up the preamp tube assignments on this amp and it actually looks like position V3 covers channels 1 and 2, so your best bet might be swapping V3 and V6. I saw on another forum where someone said they had 5150 III preamp tube problems and Fender said that a lot of 12AX7 tubes went into earlier production amps that should have been discarded.

    Great amp by the way... I used one in the backline of a benefit show I played in back in October. It was sitting on a Marshall 1960A cab and still sounded great. Very easy to dial in clean and classic gain tones I wanted with only a few minutes before our set (didn't need the red channel).

  4. #4
    Eruption
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    06.30.17 @ 01:26 AM
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    yep. check the preamp tubes. i had to replace 2 on mine.

  5. #5
    Little Dreamer sixstringer's Avatar
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    Default

    Thanks folks! Went out and bought 6 JJ ECC83-S's and replaced V1-V6.....didnt have the patience to swap out 2 and 3, but thanks for the tip, thats exactly what my local guitar guru suggested.

    Problem fixed - channel 2 defintely sounds grittier now, I never found it to be as good as everyone said, but it must have been a bad tube!

    Interesting to see what I found in the amp - two sovteks and 4 electro harmony 12AX7 EH's. I called Fender earlier and they told me I would find the JJ's in there, but not true.

    Thanks again for all your help!

  6. #6
    Hot For Teacher
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    Quote Originally Posted by sixstringer View Post
    Interesting to see what I found in the amp - two sovteks and 4 electro harmony 12AX7 EH's. I called Fender earlier and they told me I would find the JJ's in there, but not true.
    Uh oh...I thought Fender was "a company who GETS IT".

  7. #7
    Hot For Teacher 5150canuck's Avatar
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    12.20.12 @ 04:19 AM
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    Default

    I had the same kind of problem with my 5150 III, I had no gian or lack of balls on channel 2 & 3, I had a tech buddy look at the amp and my tubes were fine but he had to re sodder all the points under the socket that the tubes sit in....It is better now...

    I would buy a couple 12AX7 pre amp tubes (the amp takes 12 of them) and one by one try each one with a new one (trying your guitar after each switch out), if it turns out out to be the power tubes you will have to bias it to change those ones only.

    Good luck !
    Last edited by 5150canuck; 12.27.10 at 02:40 PM.
    [/SIGPIC]See Ya Derek !....5150canuck

  8. #8
    Hot For Teacher 5150canuck's Avatar
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    Sorry just saw that you fixed your problem after I posted..
    [/SIGPIC]See Ya Derek !....5150canuck

  9. #9
    Eruption
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    Quote Originally Posted by sixstringer View Post
    Thanks folks! Went out and bought 6 JJ ECC83-S's and replaced V1-V6.....didnt have the patience to swap out 2 and 3, but thanks for the tip, thats exactly what my local guitar guru suggested.

    Problem fixed - channel 2 defintely sounds grittier now, I never found it to be as good as everyone said, but it must have been a bad tube!

    Interesting to see what I found in the amp - two sovteks and 4 electro harmony 12AX7 EH's. I called Fender earlier and they told me I would find the JJ's in there, but not true.

    Thanks again for all your help!
    thats pathetic. a few of the very first ones came with the sovteks, but a mix? no excuse for that.

 

 

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