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  1. #1
    Eruption smme5150's Avatar
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    04.08.16 @ 04:20 PM
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    Default 5150 Combo problem- calling all amp guru's

    I have a 5150 combo that all of a sudden one day when I turned it on it suddenly had the volume level of it set on the lead post at 1. It comes on fine, you can play it but if you try to turn it up on either channel it never gets any louder than about 1?

    I just retubed the preamp tubes with JJ's and that didn't help. The power amp tubes are also JJ's and are relatively new. Now all tubes light up and get warm as always. The fuse is fine. Is this a transformer issue or something like that? Not exactly an amp tech but know my way around the basics and can't get the beast to roar~!

    MRJ? somebody please help a brotha out!

  2. #2
    Hot For Teacher dtuner317's Avatar
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    10.29.13 @ 08:27 PM
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    Output transformer. Same thing happened to me on my 5150 II head. No volume, could barely hear it. Good news is that I replaced it with a Mercury, and it never sounded better!

    As always, I have not looked at your amp, so I cant be for sure. But, it sure does sound like your output transformer is fried.

    good luck!

  3. #3
    Eruption smme5150's Avatar
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    Default Follow up to OP...

    Thanks for the reply. I have since done a few tests as suggested but I'm not sure exactly what they mean?

    1.) plugged guitar straight into effects return and the guitar was loaud as hell. Not distorted as I believe this is after preamp but loud clean breakup sound.

    2.) I plugged an extra cord from effects send to return and plugged guitar in high gain and the results where the same as always with the problem: comes on at low volume about 1 and won't go any higher.

    3.) I cleaned the High gain input, low gain input and both the effects send and returns with contact cleaner. No change

    Just wanted to add more pieces to help diagnos...

  4. #4
    Hot For Teacher dtuner317's Avatar
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    Yep, cords could be the problem as well but I look at those as no brainers. When I lost my transformer it was scratchy and I had low volume that would not adjust.

    It is a pricey repair though. Preamp tubes would not be the problem, and you say the power tubes are new. Best bet is to take it to your amp guy and have him diagnose. I would bet output transformer though.

    If you do replace, replace with a Mercury. It gave me alot more bottom end. I was pissed for the hit in the wallet, but in the end I won. It sounds better than ever. Good luck!

  5. #5
    Eruption smme5150's Avatar
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    Quote Originally Posted by dtuner317 View Post
    Yep, cords could be the problem as well but I look at those as no brainers. When I lost my transformer it was scratchy and I had low volume that would not adjust.

    It is a pricey repair though. Preamp tubes would not be the problem, and you say the power tubes are new. Best bet is to take it to your amp guy and have him diagnose. I would bet output transformer though.

    If you do replace, replace with a Mercury. It gave me alot more bottom end. I was pissed for the hit in the wallet, but in the end I won. It sounds better than ever. Good luck!
    How much is that going to set me back? Is it an easy repair?

  6. #6
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    10.26.16 @ 03:37 PM
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    Quote Originally Posted by smme5150 View Post
    Thanks for the reply. I have since done a few tests as suggested but I'm not sure exactly what they mean?

    1.) plugged guitar straight into effects return and the guitar was loaud as hell. Not distorted as I believe this is after preamp but loud clean breakup sound.

    2.) I plugged an extra cord from effects send to return and plugged guitar in high gain and the results where the same as always with the problem: comes on at low volume about 1 and won't go any higher.

    3.) I cleaned the High gain input, low gain input and both the effects send and returns with contact cleaner. No change

    Just wanted to add more pieces to help diagnos...
    It's probably not the output transformer, since you did the effects return test and it was loud. The original symptoms you were having can be that of a blow OT, but if that was the case, it wouldn't work plugging straight into the Effects return either -- and yours does. That means the amp's power section seems to be functioning properly.

    Try swapping preamp tubes around -- switch which ones are in which sockets and see if you notice a change in certain configurations. I would be willing to bet you have either a bad preamp tube (yes, new ones come defective from time to time), or a bad input jack.

    Let us know what you find.

  7. #7
    Baluchitherium
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    04.02.15 @ 07:26 AM
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    Could also be a dead cap somewhere in the amp. Check the preamp tubes first though and never touch anything inside the amp unless you know exactly what you're doing, even turned off there are huge voltages that kill you. Take it to a tech.
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  8. #8
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    10.26.16 @ 03:37 PM
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    Quote Originally Posted by tommywho5150 View Post
    Could also be a dead cap somewhere in the amp. Check the preamp tubes first though and never touch anything inside the amp unless you know exactly what you're doing, even turned off there are huge voltages that kill you. Take it to a tech.
    Yep, Tommy is right. It could also be a bad connection or cap somewhere in the preamp in addition to the things I already mentioned. But unless you are extremely familiar working on tube amps, there's nothing you yourself should do about that, so there are some other things we can check first to eliminate possible problems before you'd need to take it in to a tech.

    Your guitar direct into the effects return tests the power amp section of the amp, and a clean loud signal means it's not causing the volume loss -- which means your power tubes, surrounding circuitry, output transformer, and output jacks, etc., all are probably just fine.

    Swap the preamp tubes around like I described above, and see if certain configurations change the volume problem. (Make sure the amp is unplugged and the tubes are fairly cool when you swap them)

    After than, plug your guitar into the input jack, and push the plug side to side a little while it's plugged in. Wiggle it slowly around in the jack, and see if it cuts back to full volume, or cuts completely out. I've had 2 different 5150 combo's get back input jacks.

    The next thing to try is punch the top of the amp with the bottom of your fist while playing thru it. Don't go crazy with it, but give a few firm smacks on the tolex and see if it cuts back in, or out completely. I know this sounds like totally bogus advice -- but if your input jack is bad, the way it is secured to the chassis and PCB, giving the amp a smack on the top of it can make it cut back in temporarily, and then you'll pretty much know what the problem is.

    Again, let me know what you find.
    Last edited by mrjstudios; 02.16.12 at 05:53 PM.

  9. #9
    Hot For Teacher dtuner317's Avatar
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    10.29.13 @ 08:27 PM
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    I think I would just take it in. Just my opinion....

  10. #10
    Eruption smme5150's Avatar
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    04.08.16 @ 04:20 PM
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    Default MRJ tried everything you said...

    Ok so here is my latest update after trying the following:

    1.) As you suggested I tried wiggling around the input with my cord and trying to see if a louder volume or any crackle noises would happen. Nothing on either of the inputs. No cracks, no changes in volume etc

    2.) I tried pounding the butt end of my fist on top the amp cab while playing the guitar. Once again, nothing. No crackles, no change in the one constant volume.

    3.) I tried changing tube positions with tubes that I know are good within the new tubes from JJ's and some chinese tubes I have that I know work. Nothing! I even wiggled each tube in its socket while playing to see if I could find any cracking, popping etc. Nothing.

    4.) While doing the tube swap I also sprayed the tube input pins with contact cleaner and worked them in and out several times to insure I don't have a bad contact. Nothing-no improvement or change.


    Finally, I did notice one thing interesting: When playing the guitar during this time I noticed that the post on either channel not only when turned up produced no volume increase but conversely when I would turn both posts to 0 I still got the same volume. In other words the two posts have no effect in the 1 volume whether they are turned up or in this instance turned completely to zero. So essentially I get 1 volume level no matter what I do with the post gains! Weird!

    What next? And by the way thanks for all the suggestions thus far guys but no luck at all!

  11. #11
    Eruption smme5150's Avatar
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    Quote Originally Posted by dtuner317 View Post
    I think I would just take it in. Just my opinion....
    Probably will but I want to eliminate everything I can be sure of before I haul the 100lbs beast up from the basement and down the road. I'd hate to get it to the shop and the guy wiggle this or that and go " there you go, done!" I'm sure you know what I mean. I used to haul this fucker all over town when I used to play out and I literally don't want to haul it ever if possible! Just so damn heavy and awkward and bulky. It's brutal on my forty-something back now days!

  12. #12
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    10.26.16 @ 03:37 PM
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    Quote Originally Posted by smme5150 View Post
    Ok so here is my latest update after trying the following:

    1.) As you suggested I tried wiggling around the input with my cord and trying to see if a louder volume or any crackle noises would happen. Nothing on either of the inputs. No cracks, no changes in volume etc

    2.) I tried pounding the butt end of my fist on top the amp cab while playing the guitar. Once again, nothing. No crackles, no change in the one constant volume.

    3.) I tried changing tube positions with tubes that I know are good within the new tubes from JJ's and some chinese tubes I have that I know work. Nothing! I even wiggled each tube in its socket while playing to see if I could find any cracking, popping etc. Nothing.

    4.) While doing the tube swap I also sprayed the tube input pins with contact cleaner and worked them in and out several times to insure I don't have a bad contact. Nothing-no improvement or change.


    Finally, I did notice one thing interesting: When playing the guitar during this time I noticed that the post on either channel not only when turned up produced no volume increase but conversely when I would turn both posts to 0 I still got the same volume. In other words the two posts have no effect in the 1 volume whether they are turned up or in this instance turned completely to zero. So essentially I get 1 volume level no matter what I do with the post gains! Weird!

    What next? And by the way thanks for all the suggestions thus far guys but no luck at all!
    Ok, well now we know a few things: your power amp section is fine, your input jack is probably just fine, and it's not your preamp tubes that are bad. Unfortunately, something is wrong somewhere in the preamp section (or possibly in the reverb section... I don't recall where that is in the 5150 Combo's circuit off the top of my head), and anything more that I could tell you to do to troubleshoot it would involve opening up the amp and testing the circuit at various points -- which is NOT something you should try unless you have experience working on and building high-wattage tube amps. There are a lot of things that can zap you in tube amps, so safety first!

    At this point, you've done everything you can to eliminate any obvious/common problems, so definitely take it to a tech (if you have a good one locally), or contact Peavey to find a repair center/ship it in. If you know a good local tech, but he needs the schematics for the Combo, let me know and I can send them along. I don't know about any more, but a few years ago it was EXTREMELY hard to find schematics for the combo version online. Anyway, he will likely have to trace through the components in the preamp and check everything to find the problem, unless there is an obvious leaking busted capacitor, or something is burnt. The good news is that they will probably not have to replace any expensive components -- even the huge power filter caps in those amps are only like $5 to replace. The possibly bad news is that it may take a lot of labor hours to track down the faulty component(s), and with the way the guts of the 5150 combo are laid out, they aren't exactly easy to work on (my only complaint about the entire 5150 line of amps).

    Good luck getting it back in good shape!
    Last edited by mrjstudios; 02.16.12 at 08:50 PM.

 

 

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