Motorboating in 5E3 - that used to work

Discussion in 'Amp Tech Center' started by dragonfly66, May 9, 2019.

  1. dragonfly66

    dragonfly66 Friend of Leo's Silver Supporter

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    So I got a Tyler 20/20 in a trade. It sounds good, but when the volume is turned up I get motorboating. I called the manufacturer, who said motorboating is usually a ground issue or a filter cap issue. They offered to fix the issue at no charge if I sent the chassis to them. So I said, oh let me look around and see if I can fix it. I'll send it in if I can't find the issue easily. They told me to reflow the joints first because the F&T caps usually don't go bad.

    I reflowed some of the joints, marked in photo with yellow squares. That didn't fix it.
    tyler_2020_reflow_points.png

    So I looked on the internet and found out that to figure out which filter cap is causing the issue just take alligator clips and another cap and basically put it in parallel with each filter cap one by one. When the issue goes away that is the cap that needs replacing. So I did this and found that when I clipped the cap across the highlighted cap the issue went away. So I set out to replace that filter cap. Well after replacing that cap the motorboating didn't go away. I tested the cap once removed and it tested fine. Disappointing.

    Are there certain steps in a certain order I need to follow to find the real cause of this issue?

    5e3_layout_filtercap_hightlight.png
     
  2. Uncle Daddy

    Uncle Daddy Tele-Holic

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    Check the nuts are tight on the pots and Jack sockets too.
     
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  3. dragonfly66

    dragonfly66 Friend of Leo's Silver Supporter

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    Everything is good with the nuts on the pots and jacks. Also made sure the screws and nuts where they were used for grounding were good.

    When I tested again I noticed V3 (first power tube) seemed a bit bluer and than V4 (second power tube). So I dimmed the light so I could see the tubes better and I noticed when I turned either volume up the motorboating starts and V3's glow pulsed with the motorboating.

    I changed the power tubes to a new set and NO MOTORBOATING. Lesson learned, start with the simplest thing first.

    Even with the new tubes the first power tube seemed bluer than the second power tube. I swapped the two new power tubes and no matter which tube is in V3 position V3 is bluer than V4. Is this cause for me to check anything else?

    There is ALOT of white noise SHHHH/HISS when the volume is pass noon. With nothing plugged in. Is this just the amp or something else I need to check.
     
  4. BigDaddy23

    BigDaddy23 Tele-Meister

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    Also check the cathode bias connections - pin 8 on the 6v6's and their conection to the bias resistor and capacitor. Check their connection to ground as well....I cant quite see in the pic where that ground wire runs off to. It appears to have a bit of a weird grounding scheme....can you see where the bypass cap/resistor grounds go for V1/2? The blackmon black makes it hard to see!

    It's normal to have some hiss.Check the input jack grounds and the shunt connections there.
     
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  5. dragonfly66

    dragonfly66 Friend of Leo's Silver Supporter

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    Thank you @BigDaddy23, I will check the things you suggested.

    Here are some better photos of the filter caps and power tubes.

    20190509_102438.jpg 20190509_101609.jpg 20190509_101618.jpg 20190509_101701.jpg
     
    Last edited: May 9, 2019
  6. corliss1

    corliss1 Friend of Leo's

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    Looks like the cathode bypass cap is sitting on the resistor. The resistor will get hot and cook the cap. See if you can separate them a bit.

    If the "blue-er ness" follows the socket and not the tube, I'd certainly check voltage on each socket for comparison.
     
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  7. mherrcat

    mherrcat Tele-Holic

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    I'm guessing the bible quote is supposed to be some kind of reassurance in the event you electrocute yourself...
     
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  8. dragonfly66

    dragonfly66 Friend of Leo's Silver Supporter

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    ROFL! :lol:

    I thought about blurring it out so the amp didn't break the no religion rules of the forum.
     
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  9. clintj

    clintj Friend of Leo's

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    It's a very ironic verse to reference inside a chassis with high voltage. ;-)

    Sent from my Pixel 2 using Tapatalk
     
  10. zook

    zook Friend of Leo's

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    Replace the two 100K plate resistors with 1 watt units and the white noise shoud decrease.
     
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