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Peavey TNT150 hum

Discussion in 'Amps [BG]' started by john42654, Dec 13, 2013.

  1. john42654

    john42654

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    Hi
    Just looking to see if anyone has encountered a persistent hum from a Peavey TNT150, not super loud but annoying. It happens when the bass isnt even plugged in. None of the controls make any difference
    If anyone has any ideas ona fix please let me know

    Thanks

    John
  2. BbbyBld

    BbbyBld

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    Disclosures:
    MI Amp Engineer: Peavey Electronics
    Most likely, one (or more) of the power supply filter caps needs replacing.

    If everything works, and the only problem is the hum, that's a really easy fix for a qualified tech. I'd suggest not using it until it's looked at.
  3. heynorm

    heynorm

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    When the 150 I had in the 80's & 90's began to hum my buddy and I pulled out the chassis, looked at it, blew out any dust, plugged in a bass and it was quiet, put it back together. Did that about every two years or so, whenever the hum would return. I've heard of others who "fixed" theirs the same way. Maybe it just needs a little stink-eye from you!
  4. john42654

    john42654

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    Hi Guys,
    Thanks for the replies. Ill try taking the chassis out and giving it a good cleaning. Do you think its ok to use that electronics cleaner, the stuff that comes in the spray can? Also is there a way to identify, check and possibly replace that filter cap?
  5. BassmanPaul

    BassmanPaul Gold Supporting Member

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    If you have experience with repairing amps it would be a fairly simple job. If you have not get a tech to do the work.
  6. B-string

    B-string Supporting Member

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    If you are talking about something like "Dust-off" that is okay. Don't use a "cleaner".
    It is always possible to replace filter caps, the test equipment to check them with relative accuracy is much more expensive that the replacements will be. Unless the unit is less than 10 or 15 years old just replace them.
  7. gerryjazzman

    gerryjazzman Supporting Member

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    I had this exact problem with a TNT160 (basically the same amp) that I used to have. The hum was 120 Hz (full wave rectifier output frequency) and was independent of any volume / gain control settings. What I found was that the screws on the top of the amp that hold the chassis in could be loosened and the hum would go away. I took out the chassis to try to trace the problem. What I figured was that there was a bad connection somewhere that was associated with one of the filter caps or bypass caps on the PC board.

    With the chassis out of the cabinet it was as quiet as anything. Could never find the problem. Put the chassis back in and it was good for awhile, then it started again. Same thing with loosening the screws. I think there was some kind of microscopic break in a PCB trace or solder joint somewhere that the PCB flexing would exacerbate and cause the hum to re-appear. The way the chassis mounting is designed with the rear lip screwed to the top of the speaker cabinet and the main part of the chassis bolted to the top of the cabinet I think that the fact that the single handle on the top which has to support 75-80 lbs of cabinet causes the top of the cabinet to flex and in turn stressing and flexing the thin aluminum chassis and ultimately the PC board.

    Unfortunately I never did find the problem (it was maddening, the only issue with an amp that ever beat me). I sold the amp cheap with the disclaimer about the hum and how to "fix" it. It would be really interesting if someone actually found the issue with these.
  8. TommyKnocker

    TommyKnocker Supporting Member

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    Thanks, John for posting this thread. I have a TNT150 as well and it has a hum exactly as you described.
    I got the amp as a freebie along with the Peavey 215D that I bought from a CL ad. Until now I thought it wasn't worth trying to fix.
    It's pretty rough and appears to have been cut down from what was a TNT150 combo.
    The front panel is caved in a bit at the right end and what's left of the plywood is beat up.
    It looks like it survived a tumble from a moving vehicle.
    It does work OK, just has that hum, which really isn't noticeable when playing at what would be bar gig volumes.
    So it's good enough to be a backup.

    I'm now motivated to ask our computer tech at the office to replace the filter caps.
    He has the proper training and experience such that I'm OK with him having a go at it.
    I know he enjoys rescuing old guitar amps and stereo receivers from the trash and repairing them.

    Let us know if you do get your amp repaired and how it works out.
    And I think I'm going to look into the symptoms that gerryjazzman just described above.

    Attached Files:

  9. john42654

    john42654

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    Hi Guys

    Once again thanks for the responses. I took the amp apart over the weekend. I have to say it looks like it is really well built. No wonder it ways a ton. It didn't appear to be dusty inside but I blew it out anyway. I checked all the components by eye and checked all the hardware to make sure nothing was loose. Everything appeared to be OK. am not really familiar with the components that you guys mentioned ( filter caps ) so I cant tell if they are OK. I checked the speaker as well and that looked OK too.
    I will try Jazzmans fix and loosen the top holding screws to see if it makes any difference.
    TK, if you are able to replace those filter caps let me know
    I have a feeling bringing the amp in for repair would probably not be worth it

    On a side note Id like to know your opinions on what would be a good amp to get if I decide to replace the TNT
    Id like something loud enough to gig, mostly bars that hold maybe 200 people.
    Something that really puts out a real deep bass
    And preferably something that doesn't way a ton

    I haven't tried these amps yet but has anyone played through one of these
    Workingman SWR,
    TC Electronic.
    The new Peavey amps

    Thanks again and looking forward to your replies
  10. B-string

    B-string Supporting Member

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    Try the G-K MB200, don't let the size fool you ;).
  11. cwsbass

    cwsbass

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    Try remelting the solder joints where the input jack is mounted on the circuit board.
    Used to get a bit of a hum from my TNT150 and that turned out to be the problem.
    It's a bit of a pain as you have to remove all the knobs from the controls etc to get to the nuts behind ,undo all of them plus a few screws on the front panel. Think there's only a couple if screws hold the pcb to the chassis. Disconnect the wiring plug, then wiggle it free.
    Takes longer to take it apart than it does to remelt the joints.
    Had to do this a few times over the 25 years I've had mine.
    Hope this does the trick.

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