'73 Champ help needed

Discussion in 'Shock Brother's DIY Amps' started by String Tree, Mar 24, 2019.

  1. String Tree

    String Tree Doctor of Teleocity

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    image.jpeg it is making a horrible buzzing sound much like a shielding issue.
    The noise goes up and down with the Volume pot and, is affected by the tone pots.
    I have lots of pics from before and after the repairs.
    I had it capped and tubed a few years ago. Ran like a ... Champ.

    It was as stock as can be when I bought it.
    The guy that worked on it repaired it to keep the Stock specs going.

    One thing that happened was it once ran for a while with no speaker load.
    No idea it was.

    Any help would be appreciated, thanks in advance.

    -String Tree
     
  2. flyswatter

    flyswatter Friend of Leo's

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    Most likely a grounding issue, perhaps a ground connection to the filter caps or centre tap for the tube heaters has broken loose. Without detailed gut shots of the insides, there's no way to tell, though.

    It's unlikely the OT blew due to no-load, otherwise you'd have no output whatsoever -- and older Fenders can generally run for a while with no load if they are just idling with no signal passing through. If the amp has worked normally at all since the no load incident, I doubt that is the issue.

    One simple thing to try is swapping the preamp tube. … Problem may be located there if volume and tone are affecting it. I actually don't think the problem is tube-related, but it's always best to eliminate the simple solutions first.
     
  3. String Tree

    String Tree Doctor of Teleocity

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    The tube didn't help.
    I'll take it apart and get some pics.
     
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  4. Milspec

    Milspec Friend of Leo's

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    Did you try the other input jack....could just be a bad jack as well.
     
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  5. dan40

    dan40 Tele-Afflicted Silver Supporter

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    Since the volume and tone affect the noise level, the issue most likely lies in the input jack or the first triode of v1. As the fellas mentioned, good clear pics of those areas may help to spot the problem.
     
  6. Alamo

    Alamo Doctor of Teleocity Silver Supporter

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    That came to mind here aswell. I was watching Uncle Doug the other day
    (ok, there some major hick ups by the 1st. repair man)
    but great circling in on the probs by Uncle Doug.
    7:30 min

     
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  7. String Tree

    String Tree Doctor of Teleocity

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    Same effect on both input Jacks
     
  8. String Tree

    String Tree Doctor of Teleocity

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    image.jpeg image.jpeg
    Here we go.
    Happy to point the Camera anywhere you like.
     
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  9. String Tree

    String Tree Doctor of Teleocity

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    Two of the same pic, for some reason.
     
  10. flyswatter

    flyswatter Friend of Leo's

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    Check that grey filter cap closest in the photo (it would be the preamp fc if the three are wired in correct order). I cannot see any ground connection on the negative (the end without the detent) on that cap. If it's there, it's in a pretty weird position; it it's severed, that would def. be a source of major hum.

    I don't like at all how those caps are installed -- not professional work, IMO.

    Heaters appeared grounded so probably okay.

    Also, please train the camera in the other direction so we can see the jacks and pots -- in light of Milspec's suggestion.
     
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  11. Alamo

    Alamo Doctor of Teleocity Silver Supporter

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    Please point the cam at the two input jacks from the inside of the chassis
     
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  12. milocj

    milocj Friend of Leo's Ad Free Member

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    I'm surprised that after doing all of those filter caps a tech would have left the two original bypass caps installed, especially the bias cap.
     
  13. BigDaddy23

    BigDaddy23 Tele-Meister

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    I reckon Flyswatter is on the money - that cap looks like it has no ground.

    It would also be worthwhile reflow if the V1 socket ground. That looks a bit suspect too
     
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  14. Milspec

    Milspec Friend of Leo's

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    Cap orientation is strange and I don't like the look of the solder points either. It could have been done better....still think you need to look at those input jacks.
     
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  15. String Tree

    String Tree Doctor of Teleocity

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    Thanks everybody, I will have some more pics for you shortly.
     
  16. String Tree

    String Tree Doctor of Teleocity

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    image.jpeg image.jpeg image.jpeg image.jpeg
    V1 seems to be grounded, as does that gray Cap.
    Plus, gratuitous pics of the input Jacks.
     

    Attached Files:

    Last edited: Mar 25, 2019
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  17. String Tree

    String Tree Doctor of Teleocity

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    Always something to be learned from Uncle Doug!
     
  18. Milspec

    Milspec Friend of Leo's

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    At the input jacks, notice that pink wire....there is pinched area where the insulation is broken. What caused that to happen and can it be bleeding voltage?
     
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  19. String Tree

    String Tree Doctor of Teleocity

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    I don't know what caused it.
    I will remove both of the inputs and check it out.
     
  20. max_twang

    max_twang Tele-Afflicted

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    Not an expert at all, but here's my 0.02.

    1. Some really ugly solder joints in there. Reflow them.

    2. If the buzz is affected by the tone controls, then it arises from an issue before the tone controls. Search there first.

    3. Replace the white Mallory caps. I would do this regardless of whether they caused the buzz or not. They may or may not be causing the current issue.

    4. Have you poked around with a chopstick with the amp live. If you know how to do this safely, you might find the problem.

    5. Here's a link to Rob Robinette's website and the section on troubleshooting:

    https://robrobinette.com/Tube_Guitar_Amp_Troubleshooting.htm

    Good luck!
     
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