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Ground pilot light? 5e3 build

Discussion in 'Amp Central Station' started by deathcap, Jan 23, 2021.

  1. deathcap

    deathcap TDPRI Member

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    Still searching for this ground hum issue on a diy build.
    secondary has no center tap for the 6.3v heater filaments so I put an artificial CT on V1 and not on the pilot light.

    [​IMG]

    there are insulators between the wings and the base on the pilot light so the bulb base never touches the bracket holding it and never touches the chassis to ground. I scavenged the pilot light and can not remember what it came from. I can attach a clip to the lower wing that makes contact with the bulb base and the chassis as shown below, and the hum goes away. Can some one take a look at theirs and help me figure out what's going on here?

    [​IMG]
     
    Last edited: Jan 23, 2021
  2. Boreas

    Boreas Friend of Leo's Silver Supporter

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    Does the bulb light properly? Close-up pix of the socket connections?
     
  3. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    What do those artificial CT resistors connect to? Preamp ground? At any rate it’s an awkward reach. Have you tried them to a solder lug on a nearby socket bolt? Or near the lamp? Your clip test suggests your artificial CT is bad in some way...

    Also I can’t quite read the color codes on those resistors.
     
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  4. D'tar

    D'tar Friend of Leo's

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    What value resistor are you using for the artificial tap? I cant see the band colors clearly but the multiplier band suggest something in the 10k + range. You should be using 100 ohm resistors. Brown black brown.
     
  5. deathcap

    deathcap TDPRI Member

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    V1
    [​IMG]

    V2
    [​IMG]

    Power tubes
    [​IMG]

    Rectifier
    [​IMG]

    Pilot
    [​IMG]


    Artificial CT resistors to chassis ground are 100K 1W
     
  6. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Yes, and as @D'tar noted they should be 100R. R≠K. :)

    While we're at it, did you tell us what they're connected to? Is it the preamp ground?
     
  7. deathcap

    deathcap TDPRI Member

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    shoot, connected to pin 9 and the 4-5 pins heater wires on the preamp tube.
     
  8. deathcap

    deathcap TDPRI Member

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    the artificial CT location was temporary until I could figure out the hum. so now I know.
     
  9. deathcap

    deathcap TDPRI Member

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    Thank you
     
  10. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Sorry, I assumed that. I meant the other end. But... if temporary, it won't matter now. Let us know what you end up doing.
     
  11. deathcap

    deathcap TDPRI Member

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    the other end? the PT doesn't have a CT. I don't understand. The filaments come out of the PT and connect to the pilot, then it goes to the first power tube and continues down.
     
  12. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    NVM, let us know how it ends up and if it fixes your hum. :)
     
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  13. deathcap

    deathcap TDPRI Member

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    the other end of the resistors are connected to a bolt on the chassis. thanks again
     
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