5F11 build negative feedback help

Discussion in 'Shock Brother's DIY Amps' started by Paul Strat, Aug 16, 2019.

  1. Paul Strat

    Paul Strat Tele-Meister

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    76E56EE0-0178-4985-AF4F-2112F095AF32.jpeg
     
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  2. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Maybe a couple more pics showing the socket wiring and the area around the NFB? If that's the cause of the problem, there isn't a lot of detail of it in the pictures.

    Also, with the amp turned off, unplugged, and caps drained, the continuity setting on your meter is probably going to be the best tool to figure it all out. There's probably either a connection that shouldn't be there, or it's missing one that should be.
     
  3. D'tar

    D'tar Friend of Leo's

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    Amp off, unplugged, caps drained...

    Can you ohm the disconnected nfb feed wire to ground.
     
  4. Paul Strat

    Paul Strat Tele-Meister

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    56.9 k
     
  5. Paul Strat

    Paul Strat Tele-Meister

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  6. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Are you sure this wire from the NFB isn't shorting to ground? It looks really close to the chassis at the cut. 5f11 nfb.png
     
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  7. Paul Strat

    Paul Strat Tele-Meister

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    I think I found the issue.
    Good ole continuity is telling me I miswired the jumper that goes from the .02 cap to the 1 Meg PI grid. It’s going to the NFB resistor.
     
    Last edited: Aug 17, 2019
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  8. Paul Strat

    Paul Strat Tele-Meister

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    Although when it was miswired by bias was spot on. Now it’s freezing cold.
    -71 and <5ma
     
  9. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Stock bias resistor was way off for me.
    I ended up with 16-17k and a 10k pot.

    Sent from my XT1585 using Tapatalk
     
  10. Paul Strat

    Paul Strat Tele-Meister

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    Mine worked out with a 10k pot and the 33k range resistor. Had to drop the 10 at the bias tap down to 4.7 k. My 33k was broken and causing the cold bias issue.
     
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  11. jsnwhite619

    jsnwhite619 Friend of Leo's

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    My PT has two secondary options. I've run my 5f11 from <300v B+ to nearly 400v. I like the softer feel and lower output of the low voltage, but I figured out the trem & bass works better in the 365-375v B+ range on mine. They are great amps though. Amazing, rich clean tones and a can really rock out when you crank them.

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